Equity [Abstract] Net unrealized gains on AFS securities for which we have not recorded OTTI Accumulated Other Comprehensive Income (Loss), Net of Tax, Available-for-sale Securities, Other-than-temporary Impairment not Recorded Represents net accumulated unrealized gains (losses) appreciation on available-for-sale securities for which we have not recorded other-than-temporary impairment, net of tax, at the end of the period. Net unrealized gains on AFS securities for which we have recorded OTTI Accumulated Other Comprehensive Income (Loss), Net of Tax, Available-for-sale Gain (Loss), Other-than-temporary Impairment Recorded Represents net accumulated unrealized gains (losses) appreciation on available-for-sale securities for which we have recorded other-than-temporary impairment, net of tax, at the end of the period. Other Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax Accumulated other comprehensive income Accumulated Other Comprehensive Income (Loss), Net of Tax SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Abstract] Financing Receivable, Troubled Debt Restructuring [Table] Financing Receivable, Troubled Debt Restructuring [Table] Real Estate, Type of Property [Axis] Real Estate, Type of Property [Axis] Real Estate [Domain] Real Estate [Domain] Single-Family [Member] Single Family [Member] Multifamily [Member] Multifamily [Member] Class of Financing Receivable [Axis] Class of Financing Receivable [Axis] Class of Financing Receivable [Domain] Class of Financing Receivable [Domain] Primary [Member] Primary Mortgage Loan [Member] Consists of mortgage loans that are not included in other loan classes. Government [Member] US Government Agency Insured Loans [Member] Alt-A [Member] Alt-A Mortgage Loans [Member] Represent mortgage loans originated under a lender’s program offering reduced or alternative documentation than that required for full documentation mortgage loans but may also include other alternative product features. As a result, Alt-A mortgage loans have a higher risk of default than non-Alt-A mortgage loans. In reporting our Alt-A exposure, we have classified mortgage loans as Alt-A if the lenders that delivered the mortgage loans to us classified the loans as Alt-A based on documentation or other product features. We have loans with some features that are similar to Alt-A mortgage loans that we have not classified as Alt-A because they do not meet our classification criteria. We have classified private-label mortgage-related securities held in our investment portfolio as Alt-A if the securities were labeled as such when issued. Other [Member] Other Mortgage Loan [Member] Includes mortgage loans with higher-risk characteristics, such as interest-only loans and negative-amortizing loans that are neither government nor Alt-A. Financing Receivable, Troubled Debt Restructuring [Line Items] Financing Receivable, Troubled Debt Restructuring [Line Items] Average term extension of a single-family modified loan Financing Receivable, Modifications, Average Term Extension The following represents the average term extension (disclosed in months) resulting from loan modifications. Average interest rate reduction of a single-family modified loan Financing Receivable, Modifications, Average Interest Rate Reduction, Percentage Point The following represents the average interest rate reduction (disclosed as a %) resulting from loan modifications. Number of loans troubled debt restructurings activity Financing Receivable, Modifications, Number of Contracts Recorded investment troubled debt restructurings activity Financing Receivable, Troubled Debt Restructuring, Postmodification Investments, Debt and Equity Securities [Abstract] Available-for-sale Securities Policy Marketable Securities, Policy [Policy Text Block] Fair Value Disclosures [Abstract] Recurring Changes in Fair Value Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Fair Value Measurements Using Significant Unobservable Inputs (Level 3) Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Tabular disclosure of the fair value measurement of assets and liabilities using significant unobservable inputs (Level 3), a reconciliation of the beginning and ending balances, separately presenting changes during the period attributable to the following: (1) total gains or losses for the period (realized and unrealized), segregating those gains or losses included in earnings (or changes in net assets) and gains or losses recognized in other comprehensive income (loss), and a description of where those gains or losses included in earnings (or changes in net assets) are reported in the statement of income (or activities); (2) purchases, sales, issues, and settlements (each type disclosed separately); and (3) transfers in and transfers out of Level 3 (for example, transfers due to changes in the observability of significant inputs), by class of asset and liability. Valuation Techniques and Significant Unobservable Inputs for Level 3 Assets and Liabilities Fair Value Inputs Asset and Liabilities Quantitative Information [Table Text Block] Tabular disclosure of quantitative information about the inputs used in the fair value measurement of assets and liabilities. This disclosure may include, but is not limited to, the fair value of assets and liabilities, valuation technique used to measure fair value, the inputs used to measure fair value, the ranges of the inputs, and the weighted averages of the inputs, disclosed on the level 3 recurring fair value measurement table. Level 3 Assets Measured on Nonrecurring Basis Fair Value Measurement Inputs and Valuation Techniques [Table Text Block] Fair Value of Financial Instruments Fair Value, by Balance Sheet Grouping [Table Text Block] Fair Value Option Fair Value Option, Disclosures [Table Text Block] Risks and Uncertainties [Abstract] Allowance for loan losses and total recorded investment in HFI loans [Table] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Guaranty Book of Business [Member] Guaranty Book of Business [Member] Represents the sum of the unpaid principal balance of: (1) mortgage loans held in our mortgage portfolio; (2) Fannie Mae MBS held in our mortgage portfolio; (3) Fannie Mae MBS held by third parties; and (4) other credit enhancements that we provide on mortgage assets. It excludes non-Fannie Mae mortgage-related securities held in our investment portfolio for which we do not provide a guaranty. Product and Service [Axis] Product and Service [Axis] Product and Service [Domain] Product and Service [Domain] Original LTV ratio greater than 80% [Member] Original Loan to Value Ratio Greater than Eighty Percent [Member] Represents loans with an original loan-to-value ratio greater than 80%. Original LTV ratio less than or equal to 80% [Member] Original Loan to Value Ratio Less than or Equal to Eighty Percent [Member] Represents loans with an original loan-to-value ratio less than or equal to 80%. Current DSCR less than 100% [Member] Current Debt Service Coverage Ratio Less than One Hundred Percent [Member] Represents loans with a current debt service coverage ratio of less than 1.0. Statistical Measurement [Axis] Statistical Measurement [Axis] Statistical Measurement [Domain] Statistical Measurement [Domain] Minimum [Member] Minimum [Member] Maximum [Member] Maximum [Member] Accounts, Notes, Loans and Financing Receivable [Line Items] Accounts, Notes, Loans and Financing Receivable [Line Items] 30 days delinquent (percentage of book of business) Loans 30 to 59 Days Past Due, Percentage of Unpaid Principal Balance Represents the percentage of unpaid principal balance comprised of loans 30 to 59 days past due. Calculated based on the aggregate unpaid principal balance for the category indicated, divided by the respective book of business. Seriously delinquent (percentage of book of business) Loans Seriously Delinquent, Percentage of Unpaid Principal Balance Represents the percentage unpaid principal balance comprised of single-family loans greater than or equal to 90 days past due or multifamily loans greater than or equal to 60 days past due. Calculated based on the aggregate unpaid principal balance for the category indicated, divided by the respective book of business. Percentage of book of business Percentage of Unpaid Principal Balance of Loans Represents the percentage of unpaid principal balance of loans, by category. Loans seriously delinquent, percentage by unpaid principal balance Loans Seriously Delinquent, Unpaid Principal Balance, Percentage by Category Represents the percentage of loans that were seriously delinquent greater than 60 days. The percentage is calculated based on the unpaid principal balance of loans that were seriously delinquent divided by the aggregate unpaid principal balance of loans for each category included in our guaranty book of business. Serious delinquency: days past due Serious Delinquency Days past due 1 Represents the number of days past due required for a loan to be considered seriously delinquent. Current debt service coverage ratio reporting lag Current Debt service coverage ratio reporting lag 1 Our estimate of current debt service coverage ratios are based on the latest available income information for these properties. Although we use the most recently available results of our multifamily borrowers, there is a lag in reporting, which ranges, as they prepare their results in the normal course of business. Current Debt Service Coverage Ratio, Higher Risk Loans1 Current Debt Service Coverage Ratio, Higher Risk Loans1 A multifamily loan with the current debt service ratio ('DSCR') below 1.0 is considered one of the higher risk characteristics by our management. Concentration Risk [Table] Concentration Risk [Table] Service Providers [Axis] Service Providers [Axis] Represents service providers by type. Service Providers [Domain] Service Providers [Domain] Represents service providers. Depository Servicer [Member] Depository Servicer [Member] Represents a servicer who is a depository institution. Non-Depository Servicer [Member] Non-Depository Servicer [Member] Represents a servicer who is a non-depository institution. Concentration Risk Type [Axis] Concentration Risk Type [Axis] Concentration Risk Type [Domain] Concentration Risk Type [Domain] Credit Concentration Risk [Member] Credit Concentration Risk [Member] Insurance Service Provider Concentration Risk [Member] Insurance Service Provider Concentration Risk [Member] Reflects the concentration risk of mortgage insurance coverage by mortgage insurers as a percentage. Lender Concentration Risk [Member] Lender Concentration Risk [Member] Counterparty Name [Axis] Counterparty Name [Axis] Counterparty Name [Domain] Counterparty Name [Domain] Wells Fargo Bank N.A. [Member] Wells Fargo Bank N.A. [Member] Represents one of our largest mortgage servicer counterparties, Wells Fargo Bank N.A. Arch Capital Group Ltd. [Member] Arch Capital Group Ltd. [Member] Represents one of our largest mortgage insurer counterparties, Arch Capital Group Ltd. Group of Largest Mortgage Servicers including Affiliates [Member] Group of Largest Mortgage Servicers including Affiliates [Member] Represents the number of our largest mortgage servicers, including their affiliates. PMI [Member] PMI Mortgage Insurance Company [Member] Represents one of our largest primarily mortgage insurers, PMI Mortgage Insurance Co., which is under a various form of supervised control by their state regulator. Triad [Member] Triad Guaranty Insurance Corporation 1 [Member] Represents one of our largest primary mortgage insurers, Triad Guaranty Insurance Corporation, which is under a various form of supervised control by their state regulator. Four Major Lenders [Member] Three Major Lenders [Member] Represent the top three lenders Fannie Mae has risk sharing agreements to bear all or some portion of the credit losses on the covered loans. Radian Guaranty, Inc [Member] Radian Guaranty, Inc [Member] Represents one of our largest mortgage insurer counterparties, Radian Guaranty, Inc. Mortgage Guaranty Insurance Corp. [Member] Mortgage Guaranty Insurance Corp. [Member] Represents one of our largest mortgage insurer counterparties, Mortgage Guaranty Insurance Corp. Genworth Mortgage Insurance Corp. [Member] Genworth Mortgage Insurance Corp. [Member] Represents one of our largest mortgage insurer counterparties, Genworth Mortgage Insurance Corp. Essent Guaranty, Inc [Member] Essent Guaranty, Inc [Member] Represents one of our largest mortgage insurer counterparties, Essent Guaranty, Inc. Other counterparties [Member] Other counterparties [Member] Represents all other counterparties not presented separately in the table. Other Top Servicers [Member] Other Top Servicers [Member] Represents remaining top servicers not presented separately in the table. Walker & Dunlop, LLC [Member] Walker & Dunlop, LLC [Member] Represents one of our largest mortgage servicer counterparties, Walker & Dunlop, LLC SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Loan Type [Axis] SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Loan Type [Axis] SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Loan Type [Domain] SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Loan Type [Domain] Conventional Mortgage [Member] Conventional Mortgage [Member] Represents a mortgage loan that is not guaranteed or insured by the U.S. government or its agencies, such as the VA, the FHA or the Rural Development Housing and Community Facilities Program of the Department of Agriculture. Guarantor Obligations, Nature [Axis] Guarantor Obligations, Nature [Axis] Guarantor Obligations, Nature [Domain] Guarantor Obligations, Nature [Domain] Unconsolidated Fannie Mae MBS [Member] Non-consolidated FannieMae securities [Member] Maximum potential exposure of guarantees comprised of UPB of underlying mortgage loans that are both recognized and not recognized in our balance sheets. Population primarily consist of MBS, PLS and WL REMICS. Variable Interest Entities [Axis] Variable Interest Entities [Axis] Variable Interest Entity, Classification [Domain] Variable Interest Entity, Classification [Domain] Variable Interest Entity, Not Primary Beneficiary [Member] Variable Interest Entity, Not Primary Beneficiary [Member] Concentration Risk [Line Items] Concentration Risk [Line Items] Percentage of Loans with Detailed Loan Level Information Percentage of Loans with Detailed Loan Level Information Represents the percentage of loans with detailed loan level information available. Primary mortgage insurance coverage risk in force Primary Mortgage Insurance Coverage Risk in Force Represents our maximum potential loss recovery under the applicable primary mortgage insurance policies. Mortgage insurance coverage risk in force Mortgage Insurance Coverage Risk In Force Mortgage Insurance Coverage 'risk in force' represents our maximum potential loss recovery under the applicable mortgage insurance policies. Mortgage insurance coverage risk in force as a percentage of book of business Total Mortgage Insurance Coverage Risk in Force as Percentage of Unpaid Principal Balance in Guaranty Book of Business Represents mortgage insurance coverage risk in force as a percentage of unpaid principal balance. Pool mortgage insurance coverage risk in force Pool Mortgage Insurance Coverage Risk in Force Represents our maximum potential loss recovery under the applicable pool mortgage insurance policies. Concentration Risk, Percentage Concentration Risk, Percentage Mortgage insurance coverage risk in force for insurers with credit quality deterioration Mortgage Insurance Coverage Risk in Force, Insurers with Publicly Disclosed Financial Weakness Amount represents risk in force mortgage insurance coverage provided by the mortgage insurers with publicly disclosed financial weaknesses. Mortgage insurance coverage risk in force percentage to be paid in cash Mortgage Insurance Coverage Risk in Force, Insurance Claim, Percentage To be Paid in Cash by Mortgage Insurer Mortgage Insurance Coverage Risk in Force, Insurance Claim, Percentage To be Paid in Cash by Mortgage Insurer Mortgage insurance coverage risk in force percentage to be deferred Mortgage Insurance Coverage Risk in Force, Insurance Claim, Percentage To be Deferred by Mortgage Insurer Mortgage Insurance Coverage Risk in Force, Insurance Claim, Percentage To be Deferred by Mortgage Insurer Estimated benefit included in combined loss reserves Insurance Loss Reserves, Contractual Mortgage Insurance Benefit, Net Estimated benefit included in total loss reserves is the contractual mortgage insurance benefits under mortgage insurance policies net of the adjustment for collectability for our mortgage insurer counterparties' inability to fully pay the contractual mortgage insurance claims. Receivable from claims on insured, defaulted loans excluding government insured loans Receivable from Claims on defaulted loans from Mortgage Insurers Sellers and Servicers Amount due in settlement of a claim for reimbursement from an insurance company (insurers) and sellers/servicers when the Company has suffered a loss covered under the terms of an insurance policy or a seller/servicer contract. Allowance for mortgage insurance receivable Allowance for Mortgage Insurance Receivable The amount of the valuation allowance recorded as of the balance sheet date pertaining to the specified mortgage insurance receivable for which an assessment was made that a portion of such mortgage insurance receivable will not be collected. Maximum potential loss recovery from lenders under risk sharing agreements Loss Contingency, Related Receivable, Maximum Represent maximum loss recovery from lenders under risk share agreements. Percentage of concentration risk Percentage of Concentration Risk For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division. Number of Insurance Companies Who Provided Majority of Mortgage Insurance Number of Insurance Companies Who Provided Majority of Mortgage Insurance Represents the number of insurance companies who provided the majority of our mortgage insurance. Concentration Risk, Number of Lenders, Maximum Potential Loss Recovery Concentration Risk, Number of Lenders, Maximum Potential Loss Recovery Represent the number of lenders covering the majority of our maximum potential loss recovery. Number of Largest Mortgage Servicers Servicing Majority of Guaranty Book of Business Number of Largest Mortgage Servicers Servicing Majority of Guaranty Book of Business Represents the number of our largest mortgage servicers, including their affiliates, servicing the majority of our guaranty book of business. Debt Disclosure [Abstract] Short-Term and Long-Term Debt Debt Disclosure [Text Block] Financing Receivable, Credit Quality Indicator [Table] Financing Receivable, Credit Quality Indicator [Table] Credit Quality Indicator [Axis] Internal Credit Assessment [Axis] Financing Receivable, by Credit Quality Indicator [Domain] Internal Credit Assessment [Domain] Non-classified [Member] Non-Classified [Member] A category of financing receivables not classified as either substandard or doubtful. Doubtful [Member] Doubtful [Member] Total classified [Member] Classified [Member] Credit rating classification which identifies weaknesses related to credit risk, including Substandard and Doubtful classifications. Financing Receivable, Credit Quality Indicator [Line Items] Financing Receivable, Credit Quality Indicator [Line Items] Total recorded investment Recorded Investment Mortgage Loans Held For Investment Recorded investment in mortgage loans held-for-investment, excluding loans for which we have elected the fair value option, by portfolio segment. Recorded investment consists of unpaid principal balance, unamortized premiums, discounts and other cost basis adjustments, and accrued interest receivable. Consolidations and Transfers of Financial Assets [Abstract] Consolidations and Transfers of Financial Assets Consolidations And Transfers Of Financial Assets [Text Block] The entire disclosure for consolidation of the reporting entity. Provides users with an understanding of (1) the significant judgments and assumptions made by an enterprise in determining whether it must consolidate a VIE and/or disclose information about its involvement with a VIE, (2) the nature of restrictions on a consolidated VIE's assets reported by an enterprise in its statement of financial position, including the carrying amounts of such assets, (3) the nature of, and changes in, the risks associated with an enterprise's involvement with the VIE, and (4) how an enterprise's involvement with the VIE affects the enterprise's financial position, financial performance, and cash flows. The entire disclosure for a transferor's continuing involvement in financial assets that it has transferred in a securitization or asset-backed financing arrangement, the nature of any restrictions on assets reported by an entity in its statement of financial position that relate to a transferred financial asset (including the carrying amounts of such assets), how servicing assets and servicing liabilities are reported, and (for securitization or asset-backed financing arrangements accounted for as sales) when a transferor has continuing involvement with the transferred financial assets and transfers of financial assets accounted for as secured borrowings, how the transfer of financial assets affects an entity's financial position, financial performance, and cash flows. Fair Value Measurement Inputs and Valuation Techniques [Table] Fair Value Measurement Inputs and Valuation Techniques [Table] Measurement Input Type [Axis] Measurement Input Type [Axis] Measurement Input Type [Domain] Measurement Input Type [Domain] Measurement Input, Constant Prepayment Rate [Member] Measurement Input, Constant Prepayment Rate [Member] Measurement Input, Loss Severity [Member] Measurement Input, Loss Severity [Member] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Weighted Average [Member] Weighted Average [Member] Asset Class [Axis] Asset Class [Axis] Asset Class [Domain] Asset Class [Domain] Other mortgage-related securities [Member] Mortgage Backed Securities, Other [Member] Measurement Frequency [Axis] Measurement Frequency [Axis] Measurement Frequency [Domain] Measurement Frequency [Domain] Fair Value, Recurring [Member] Fair Value, Recurring [Member] Fair Value, Nonrecurring [Member] Fair Value, Nonrecurring [Member] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value Hierarchy and NAV [Domain] Significant Other Observable Inputs (Level 2) [Member] Fair Value, Inputs, Level 2 [Member] Significant Unobservable Inputs (Level 3) [Member] Fair Value, Inputs, Level 3 [Member] Business Segments [Axis] Segments [Axis] Segment [Domain] Segments [Domain] Valuation Approach and Technique [Axis] Valuation Approach and Technique [Axis] Valuation Approach and Technique [Domain] Valuation Approach and Technique [Domain] Single vendor with inputs [Member] Single Vendor With Inputs [Member] For securities, loans and debt, his valuation technique estimates fair value based upon prices received from one specific vendor. These fair values are validated at the security level therefore inputs have been disclosed. Consensus without inputs [Member] Consensus Without Inputs [Member] Valuation methodology used to estimate the fair value of certain securities, loans and debt. This methodology uses multiple vendor prices (active market participants) to estimate fair value. These fair values are not validated at the security level therefore inputs have not been disclosed. Single vendor without inputs [Member] Single Vendor Without Inputs [Member] For securities, loans and debt, this valuation technique estimates fair value based upon prices received from one specific vendor. These fair values are not validated at the security level therefore inputs have not been disclosed. Other valuation technique [Member] Other Valuation Technique [Member] Other valuation techniques which have been used for fair value during the period reported which are not otherwise provided for in the existing taxonomy in the form of Domain Members or individual elements. Internal model [Member] Internal Model [Member] Internal Model is a valuation technique to estimate the fair value of loans, acquired property and other assets using the value of the underlying collateral. The inputs into this internal model include property level data such as prior sales prices, tax assessment values, property characteristics, and historical foreclosure sales data. Derivatives use an internal model that is based on market data adjusted for market movement. Asset Manager Estimate [Member] Asset Manager Estimate [Member] Valuation technique uses the net operating income and tax assessments of the specific acquired property, other asset, or collateral underlying the loan as well as MSA-specific market capitalization rates and average per unit sales values to estimate property fair value. Accepted Offers [Member] Accepted Offers [Member] Accepted Offers represent an agreement in principle to transact acquired properties. Appraisals [Member] Appraisals [Member] An appraisal is a valuation techniques to estimate the fair value of a specific acquired property, other asset or collateral underlying a loan by a certified or licensed appraiser, in accordance with the Uniform Standards of Professional Appraisal Practice. Walk Forwards [Member] Walk Forwards [Member] Techniques to adjust appraisal and broker price opinion valuations for changing market conditions by applying a walk forward factor based on local price movements since the time the third-party value was obtained. Proprietary Home Price Model and Appraisals [Member] Proprietary Home Price Model and Appraisals [Member] Represent the aggregation of the following two models. Internal Model is a valuation technique to estimate the fair value of loans using the value of the underlying collateral. The inputs into this internal model include property level data such as prior sales prices, tax assessment values, property characteristics, and historical foreclosure sales data. An appraisal is a valuation technique to estimate the fair value of a specific property by a certified or licensed appraiser, in accordance with the Uniform Standards of Professional Appraisal Practice. Discounted cash flow with inputs [Member] Discounted Cash Flow with Inputs [Member] Fair value estimates for securities and certain consolidated MBS debt with embedded derivatives are derived using a discounted cash flow technique. This technique uses inputs such as default rates, prepayment speeds, loss severity and spreads. The fair value of a portion of our senior-subordinated trust structures are estimated using discounted cash flow at the security level as a proxy for estimating loan fair value. This valuation technique uses unobservable inputs such as prepayment speeds, spreads, and loss severities to estimate the fair value of our securities. These inputs are weighted in a model that calculates the expected cash flow of the security which is used as the basis of fair value. These loans are classified as Level 3 of the valuation hierarchy because significant inputs are unobservable. For structured debt instruments cash flows are evaluated taking into consideration any structured derivatives through which we have swapped out of the structured features of the notes. The resulting cash flows are discounted to present value using a yield curve derived from market prices observed for Fannie Mae Benchmark Notes and adjusted to reflect fair values at the offer side of the market. Market swaption volatilities are also referenced for the valuation of callable structured debt instruments. Since the derivatives considered in the valuations of these structured debt instruments are classified as level 3 of the valuation hierarchy, the valuations of the structured debt instruments result in a level 3 classification. These fair values are validated at the security level therefore inputs have been disclosed. Fair Value Inputs, Quantitative Information [Line Items] Fair Value, Option, Quantitative Disclosures [Line Items] Fair Value Inputs Basis Spread Fair Value Inputs Basis Spread Risk associated with risk of default, credit spread risk and downgrade risk, expressed as a basis point, used as an input to measure fair value. Mortgage loans held for sale, at lower of cost or fair value Mortgages Held-for-sale, Fair Value Disclosure Mortgage loans held for investment, at fair value Loans Receivable, Fair Value Disclosure Acquired property, net Real Estate Acquired through Foreclosure, Fair Value Disclosure Carrying amount as of the balance sheet date of real estate owned and foreclosed assets. Foreclosed assets include all assets obtained in full or partial satisfaction of a debt arrangement through foreclosure proceedings. Total nonrecurring assets at fair value Assets, Fair Value Disclosure Number of properties measured Number of Acquired Properties Valuated, Percentage The percentage of acquired property valued using different valuation techniques based on the number of properties. Debt Securities, Available-for-sale, Measurement Input Debt Securities, Available-for-sale, Measurement Input Segment Reporting [Abstract] Reconciliation of Assets from Segment to Consolidated [Table] Reconciliation of Assets from Segment to Consolidated [Table] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Operating Segments [Member] Operating Segments [Member] Segment Reporting, Asset Reconciling Item [Line Items] Segment Reporting, Asset Reconciling Item [Line Items] Assets Assets SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate Schedule [Table] SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate Schedule [Table] SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] Loans in Mortgage Portfolio Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Aging Analysis PastDueFinancingReceivablesTableTextBlock [Table Text Block] Tabular disclosure of financing receivables that are current, past due and impaired, financing receivables that are 90 days past due and still accruing, and financing receivables on nonaccrual status. Credit Quality Indicators Financing Receivable Credit Quality Indicators [Table Text Block] Individually Impaired Loans Impaired Financing Receivables [Table Text Block] Troubled Debt Restructurings Activity Financing Receivable, Troubled Debt Restructuring [Table Text Block] Income Tax Disclosure [Abstract] Schedule of Components of Income Tax Expense (Benefit) Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] Schedule of Effective Income Tax Rate Reconciliation Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Schedule of Deferred Tax Assets and Liabilities Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Schedule of Unrecognized Tax Benefits Roll Forward Schedule of Unrecognized Tax Benefits Roll Forward [Table Text Block] Schedule of Available-for-sale Securities [Table] Schedule of Available-for-sale Securities [Table] Financial Instrument [Axis] Financial Instrument [Axis] Financial Instruments [Domain] Financial Instruments [Domain] Fannie Mae [Member] Federal National Mortgage Association Certificates and Obligations (FNMA) [Member] Alt-A and subprime private-label securities [Member] Mortgage-backed Securities, Issued by Private Enterprises [Member] Mortgage revenue bonds [Member] US States and Political Subdivisions Debt Securities [Member] Debt Securities, Available-for-sale [Line Items] Debt Securities, Available-for-sale [Line Items] Less Than 12 Consecutive Months, Gross Unrealized Losses Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss Less Than 12 Consecutive Months, Fair Value Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value 12 Consecutive Months or Longer, Gross Unrealized Losses Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 12 Consecutive Months or Longer, Fair Value Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value Fair Value Fair Value Disclosures [Text Block] Commitments and Contingencies Disclosure [Abstract] Non Cancelable Future Commitments by Remaining Maturity [Table Text Block] Contractual Obligation, Fiscal Year Maturity [Table Text Block] Schedule of Trading Securities and Other Trading Assets [Table] Debt Securities, Trading, and Equity Securities, FV-NI [Table] Mortgage-related securities [Member] Collateralized Mortgage Backed Securities [Member] Other agency [Member] Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] U.S. Treasury Securities [Member] US Treasury Securities [Member] Debt Security, Corporate, US [Member] Debt Security, Corporate, US [Member] Non-mortgage-related securities [Member] Non-mortgage-related securities [Member] Represents non-mortgage-related securities in our trading securities, which includes our U.S. Treasury securities and other securities that currently contains domestic corporate debt securities. Schedule of Investments in Trading Securities [Line Items] Debt and Equity Securities, FV-NI [Line Items] Trading, at fair value Debt Securities, Trading Variable Interest Entity, Conclusion to Consolidate, Change in Facts and Circumstances, Amount Variable Interest Entity, Conclusion to Consolidate, Change in Facts and Circumstances, Amount Impact of the change in conclusion to consolidate a Variable Interest Entity (VIE) in the most recent financial statements (for example, the VIE was previously consolidated and is not currently consolidated) and the dollar amount of the change on the reporting entity's financial statements. Broker-Dealer, Net Capital Requirement, SEC Regulation [Abstract] Regulatory Capital Classification Measures Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations [Table Text Block] Segment Reporting Policy Segment Reporting, Policy [Policy Text Block] Schedule of Impaired Financing Receivable [Table] Schedule of Impaired Financing Receivable [Table] Single Family [Member] Financing Receivable, Impaired [Line Items] Financing Receivable, Impaired [Line Items] Individually impaired loans with related allowance recorded: average recorded investment Impaired Financing Receivable, with Related Allowance, Average Recorded Investment Individually impaired loans with related allowance recorded: total interest income recognized Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method Individually impaired loans with related allowance recorded: interest income recognized on a cash basis Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method Individually impaired loans with no related allowance recorded: average recorded investment Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment Individually impaired loans with no related allowance recorded: total interest income recognized Impaired Financing Receivable, with No Related Allowance, Interest Income, Accrual Method Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method Individually impaired loans: average recorded investment Impaired Financing Receivable, Average Recorded Investment Individually impaired loans: total interest income recognized Impaired Financing Receivable, Interest Income, Accrual Method Individually impaired loans: interest income recognized on a cash basis Impaired Financing Receivable, Interest Income, Cash Basis Method Table Footnote [Abstract] Table Footnote [Abstract] Represents a tabular schedule for the footnotes to a table. Quarterly Financial Information Disclosure [Abstract] Interest income: Interest and Dividend Income, Operating [Abstract] Trading securities Interest and Dividend Income, Securities, Operating, Trading or Measured at Fair Value Available-for-sale securities Interest and Dividend Income, Securities, Operating, Available-for-sale Mortgage loans interest income Interest and Fee Income, Loans and Leases Interest Income, Federal Funds Sold and Securities Purchased under Agreements to Resell Interest Income, Federal Funds Sold and Securities Purchased under Agreements to Resell Other Other Interest and Dividend Income Total interest income Interest and Dividend Income, Operating Interest expense: Interest Expense [Abstract] Short-term debt interest expense Interest Expense, Short-term Borrowings Long-term debt interest expense Interest Expense, Long-term Debt Total interest expense Interest Expense Net interest income Interest Income (Expense), Net Benefit (provision) for credit losses Provision for Loan, Lease, and Other Losses Net interest income after benefit for credit losses Interest Income (Expense), after Provision for Loan Loss Investment gains (losses), net Investment Gains Loss Net 1 Our Investment gains (losses) consists of (1) gains/losses from sale of AFS securities; (2) gains/losses on securitization of loans and securities from our retained mortgage portfolio; (3) gains/losses on consolidation/deconsolidation of securities; (4) lower of cost or fair value adjustments on held-for-sale loans, and other investment gains/losses; and (5) net other-than-temporary impairments. Fair value gains (losses), net Fair Value Gains Losses Net Consists of (1) derivatives fair value gains and losses; (2) trading securities gains and losses; (3) foreign exchange gains and losses on foreign-denominated debt; (4) fair value gains and losses on certain debt securities carried at fair value; and (5) fair value gains and losses on loans carried at fair value. Fee and other income Noninterest Income, Other Operating Income Non-interest income Noninterest Income Salaries and employee benefits Labor and Related Expense Professional services Professional and Contract Services Expense Other administrative expenses Other General and Administrative Expense Total administrative expenses General and Administrative Expense Foreclosed property expense Foreclosed Real Estate Expense (Income) Amount of expense (income) recognized during the period for the foreclosure on real estate assets. Temporary Payroll Cut Continuation Act of 2011 (TCCA) fees Single-Family Guaranty Fee, Temporary Payroll Tax Cut Continuation Act of 2011 Represents single-family guaranty fees related to Temporary Payroll Tax Cut Continuation Act of 2011 (“TCCA”) recognized during the period which is payable to U.S. Treasury. Other expenses, net Other Noninterest Expense Total expenses Noninterest Expense Income before federal income taxes Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Provision for federal income taxes Income Tax Expense (Benefit) Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Dividends distributed or available for distribution to senior preferred stockholder Preferred Stock Dividends and Other Adjustments Net income (loss) attributable to common stockholders Net Income (Loss) Available to Common Stockholders, Basic Earnings (loss) per share: Basic Earnings Per Share, Basic Earnings (loss) per share: Diluted Earnings Per Share, Diluted Weighted-average common shares outstanding: Basic Weighted Average Number of Shares Outstanding, Basic Weighted-average common shares outstanding: Diluted Weighted Average Number of Shares Outstanding, Diluted Guarantees [Abstract] Financial Guarantees Guarantees [Text Block] Unconditional Purchase Obligation [Table] Unconditional Purchase Obligation [Table] Describes each unconditional purchase obligation (recorded and unrecorded) arrangement to purchase goods and services that extend over multiple periods, any assets pledged to secure payment, and the fixed or determinable amount of payments due in each of the next five years and thereafter. Also includes contractual obligations. Derivative Instrument Risk [Axis] Derivative Instrument [Axis] Derivative Contract Type [Domain] Derivative Contract [Domain] Mortgage commitment derivatives Mortgage Commitment Derivatives [Member] Represents a forward-based arrangement to purchase or sell mortgages-related securities and to purchase single-family mortgages in the secondary market. Unconditional Purchase Obligation [Line Items] Unconditional Purchase Obligation [Line Items] Describes each unconditional purchase obligation (recorded and unrecorded) arrangement to purchase goods and services that extend over multiple periods, any assets pledged to secure payment, and the fixed or determinable amount of payments due in each of the next five years and thereafter. Also includes contractual obligations. Operating Leases, Rent Expense Operating Leases, Rent Expense Loans and Mortgage-Related Securities [Abstract] Purchase Obligation, Fiscal Year Maturity [Abstract] 2020 Purchase Obligation, Due in Next Twelve Months 2021 Purchase Obligation, Due in Second Year 2022 Purchase Obligation, Due in Third Year 2023 Purchase Obligation, Due in Fourth Year 2024 Purchase Obligation, Due in Fifth Year Thereafter Purchase Obligation, Due after Fifth Year Total Purchase Obligation Operating Leases [Abstract] Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract] 2020 Operating Leases, Future Minimum Payments Due, Next Twelve Months 2021 Operating Leases, Future Minimum Payments, Due in Two Years 2022 Operating Leases, Future Minimum Payments, Due in Three Years 2023 Operating Leases, Future Minimum Payments, Due in Four Years 2024 Operating Leases, Future Minimum Payments, Due in Five Years Thereafter Operating Leases, Future Minimum Payments, Due Thereafter Total Operating Leases, Future Minimum Payments Due Other [Abstract] Other Commitment, Fiscal Year Maturity [Abstract] 2020 Other Commitment, Due in Next Twelve Months 2021 Other Commitment, Due in Second Year 2022 Other Commitment, Due in Third Year 2023 Other Commitment, Due in Fourth Year 2024 Other Commitment, Due in Fifth Year Thereafter Other Commitment, Due after Fifth Year Total Other Commitment Conventional Mortgage [Member] Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] Midwest [Member] Midwest United States [Member] Midwest includes IL, IN, IA, MI, MN, NE, ND, OH, SD, WI. Northeast [Member] Northeast United States [Member] Northeast includes CT, DE, ME, MA, NH, NJ, NY, PA, PR, RI, VT, VI Southeast [Member] Southeast United States [Member] Southeast includes AL, DC, FL, GA, KY, MD, NC, MS, SC, TN, VA, WV Southwest [Member] Southwest United States [Member] Southwest includes AZ, AR, CO, KS, LA, MO, NM, OK, TX, UT West [Member] West United States [Member] West includes AK, CA, GU, HI, ID, MT, NV, OR, WA and WY. New Accounting Guidance [Abstract] New Accounting Guidance [Abstract] Prospective Adoption of New Accounting Pronouncements [Table] Prospective Adoption of New Accounting Pronouncements [Table] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Accounting Standards Update 2016-13 [Member] Accounting Standards Update 2016-13 [Member] Scenario [Axis] Scenario [Axis] Scenario [Domain] Scenario [Domain] Forecast [Member] Forecast [Member] Item Effected [Line Items] Item Effected [Line Items] Cumulative Effect of New Accounting Principle in Period of Adoption Cumulative Effect of New Accounting Principle in Period of Adoption Statement of Cash Flows [Abstract] Statement [Table] Statement [Table] Consolidated Trusts [Member] Variable Interest Entity, Primary Beneficiary [Member] Consolidated Entities [Axis] Consolidated Entities [Axis] Consolidated Entities [Domain] Consolidated Entities [Domain] Fannie Mae [Member] Parent Company [Member] Statement [Line Items] Statement [Line Items] Cash flows provided by (used in) operating activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Net income Reconciliation of net income to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Amortization of cost basis adjustments Depreciation, Amortization and Accretion, Net Benefit for credit losses Valuation gains Valuation Loss (Gain) Includes the following non-cash items that flow through Investment gains (losses): (1) lower cost or market adjustment on whole loans; (2) the impact of securities and loan derecognition under a sale; (3) realized gains (losses) on securitizations; and (4) the impact of consolidation, deconsolidation and other-than-temporary impairment of available-for-sale securities. Additionally, this line includes fair value losses (gains) on trading securities, debt and derivatives. Current and deferred federal income taxes Increase (Decrease) in Income Taxes Payable, Net of Income Taxes Receivable Net gains related to the disposition of acquired property and preforeclosure sales, including credit enhancements Net Gains Related To The Disposition of Acquired Property and Preforeclosure Sales, Including Credit Enhancements Represents Net Gains Related To The Disposition of Acquired Property and Preforeclosure Sales, Including Credit Enhancements which are reconciling items to operating income which are included in the proceeds from dispositions of acquired property and preforeclosure sales within the investing section. Other, net Other Operating Activities, Cash Flow Statement Net change in trading securities Increase (Decrease) in Debt Securities, Trading, and Equity Securities, FV-NI Interest Paid, Excluding Capitalized Interest, Operating Activities Interest Paid, Excluding Capitalized Interest, Operating Activities Net cash provided by (used in) operating activities Net Cash Provided by (Used in) Operating Activities Cash flows provided by investing activities: Net Cash Provided by (Used in) Investing Activities [Abstract] Proceeds from maturities and paydowns of trading securities held for investment Proceeds from Maturities, Repayments and Calls of Debt Securities, FV-NI, Held-for-investment Proceeds from sales of trading securities held for investment Proceeds from Sale of Debt and Equity Securities, FV-NI, Held-for-investment Proceeds from maturities and paydowns of available-for-sale securities Proceeds from Maturities, Prepayments and Calls of Debt Securities, Available-for-sale Proceeds from sales of available-for-sale securities Proceeds from Sale of Debt Securities, Available-for-sale Purchases of loans held for investment Payments to Acquire Loans Held-for-investment Proceeds from repayments of loans acquired as held for investment Proceeds from Principal Repayments on Loans and Leases Held-for-investment Proceeds from sales of loans acquired as held for investment Proceeds from Sale of Loans and Leases Held-for-investment Advances to lenders Payments For Advances To Lenders Advances to lenders represent payments of cash in exchange for the receipt of mortgage loans from lenders in a transfer that is accounted for as a secured lending arrangement. Proceeds from disposition of acquired property and preforeclosure sales Proceeds from Sale of Foreclosed Assets Net change in federal funds sold and securities purchased under agreements to resell or similar arrangements Proceeds from (Payments for) Federal Funds Sold and Securities Purchased under Agreements to Resell, Net Other, net Payments for (Proceeds from) Other Investing Activities Net cash provided by investing activities Net Cash Provided by (Used in) Investing Activities Cash flows used in financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Proceeds from the issuance of debt Proceeds from Issuance of Debt Payments to redeem debt Repayments of Debt Payments of cash dividends on senior preferred stock to Treasury Payment Of Cash Dividends On Senior Preferred Stock To Treasury Payment of cash dividends on senior preferred stock to Treasury. Proceeds from senior preferred stock purchase agreement with Treasury Proceeds From Senior Preferred Stock Agreement With Us Treasury Represents the cash received from US Treasury pursuant to senior preferred purchase agreement attributed by our net worth deficit at prior quarter end Other, net Proceeds from (Payments for) Other Financing Activities Net cash used in financing activities Net Cash Provided by (Used in) Financing Activities Net increase (decrease) in cash, cash equivalents and restricted cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect Cash, cash equivalents and restricted cash at beginning of period Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Cash, cash equivalents and restricted cash at end of period Cash paid during the period for: Payments for Operating Activities [Abstract] Interest Interest Paid, Including Capitalized Interest, Operating and Investing Activities Income taxes Income Taxes Paid Non-cash activities: Supplemental Cash Flow Information [Abstract] Net mortgage loans acquired by assuming debt Noncash or Part Noncash Acquisition, Debt Assumed Net transfers from mortgage loans of Fannie Mae to mortgage loans of consolidated trusts Transfers From Loans Held For Investment Of Parent Company To Loans Held For Investment Of Consolidated Trusts Represents net transfers to (from) mortgage loans held for investment of consolidated trusts from (to) mortgage loans held for investment of Fannie Mae. Transfers from advances to lenders to loans held for investment of consolidated trusts Net Transfers From Advances to Lenders to Loans Held for Investment of Consolidated Trusts1 Represents net transfers of MBS securities created as a result of the Early Lender sale program to loans held for investment of consolidated trusts. Net transfers from mortgage loans to acquired property Real Estate Owned, Transfer to Real Estate Owned Schedule of Selected Quarterly Financial Information Quarterly Financial Information [Table Text Block] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Accumulated Other Comprehensive Income (Loss) AOCI Attributable to Parent [Member] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Statutory corporate tax rate Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward] AOCI Attributable to Parent, Net of Tax [Roll Forward] Beginning balance Stockholders' Equity Attributable to Parent Total other comprehensive loss Other Comprehensive Income (Loss), Net of Tax Ending balance Component of statutory minimum capital requirement, percentage of the unpaid principal balance of outstanding Fannie Mae MBS held by third parties Component of Statutory Minimum Capital Requirement, Percentage of Unpaid Principal Balance of Fannie Mae MBS Held by Third Parties Represents a percentage of unpaid principal balance of Fannie Mae MBS Held by third parties which is a component of Statutory Minimum Capital requirement as determined by FHFA, our regulator. Component of critical capital requirement, percentage of the unpaid principal balance of outstanding Fannie Mae MBS held by third parties Component of Critical Capital Requirement, Percentage of Unpaid Principal Balance of Fannie Mae MBS Held by Third Parties Represents a percentage of unpaid principal balance of Fannie Mae MBS Held by third parties which is a component of Critical Capital requirement as determined by FHFA, our regulator. Net worth (deficit) Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Core capital Capital Statutory minimum capital requirement Capital Required for Capital Adequacy Deficit of core capital over statutory minimum capital requirement Deficit Of Core Capital Over Statutory Minimum Capital Requirement Represents the deficit of core capital over statutory minimum capital requirement. Component of statutory minimum capital requirement, percentage of on-balance sheet assets, except those underlying Fannie Mae MBS held by third parties Component of Statutory Minimum Capital Requirement, Percentage of On-Balance Sheet Assets, Except Those Underlying Fannie Mae MBS Held by Third Parties Represents a percentage of On-Balance Sheet Assets, except those underlying Fannie Mae MBS held by third parties which is a component of statutory minimum capital requirement as defined by FHFA, our regulator. Component of statutory minimum capital requirement, maximum percentage of other off-balance sheet obligations Component of Statutory Minimum Capital Requirement, Percentage of Off-Balance Sheet Obligations, Maximum Represents a maximum percentage of Off-Balance Sheet obligations which is a component of statutory minimum capital requirements. Component of critical capital requirement, percentage of on-balance sheet assets, except those underlying Fannie Mae MBS held by third parties Component of Critical Capital Requirement, Percentage of On-Balance Sheet Assets, Except Those Underlying Fannie Mae MBS Held by Third Parties Represents a percentage of On-Balance sheet assets, except those underlying Fannie Mae MBS held by third parties which is a component of Critical Capital requirement. Component of critical capital requirement, percentage of other off-balance sheet obligations Component of Critical Capital Requirement, Percentage of Off-Balance Sheet Obligations Represents a percentage of Off-Balance Sheet Obligations which a component of Critical Capital requirement as determined by FHFA, our regulator. Schedule of Related Party Transactions, by Related Party [Table] Schedule of Related Party Transactions, by Related Party [Table] Related Party [Axis] Related Party [Axis] Related Party [Domain] Related Party [Domain] US Treasury [Member] US Treasury [Member] Represent the company's related transactions with the U.S. Treasury. Related Parties [Line Items] Related Party Transaction [Line Items] Aggregate funding received from US Treasury pursuant to the senior preferred stock purchase agreement Aggregate Funding Received From US Treasury Pursuant To the Senior Preferred Stock Purchase Agreement Represents the aggregated funding received to date from U.S. Treasury under the terms of the senior preferred stock purchase agreement. Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Capital Reserve Amount, Fiscal Year, Senior Preferred Stock Purchase Agreement, Amendment Capital Reserve Amount, Fiscal Year, Senior Preferred Stock Purchase Agreement, Amendment Represents the amount of capital the company is allowed to reserve for the fiscal year per the amended senior preferred stock purchase agreement between the company and U.S. Treasury. Fair Value Inputs Quantitative Information [Table] Schedule of the inputs used in the fair value measurement of assets and liabilities. This disclosure may include, but is not limited to, the fair value of the asset and liability, valuation technique used to measure fair value, the inputs used to measure fair value, the ranges of the inputs, and the weighted averages of the inputs. Fair Value, Inputs, Level 2 [Member] Recurring Fair Value Measurements [Member] Dealer Mark [Member] Dealer Mark [Member] Valuation techniques for highly complex structured swaps primarily use a single dealer mark due to lack of transparency in the market and may be modeled using observable interest rates and volatility levels as well as significant unobservable assumptions, resulting in Level 3 classification of the valuation hierarchy. Fair Value by Asset Class [Domain] Agency [Member] US Government Corporations and Agencies Securities [Member] Other [Member] Trading Securities [Member] (Deprecated 2018-01-31) Trading Assets, Excluding Debt and Equity Securities [Member] Available-for-sale securities [Member] Available-for-sale Securities [Member] Mortgage loans [Member] Mortgages [Member] Long-term debt [Member] Long-term Debt [Member] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Senior floating [Member] Senior Floating Debt [Member] Senior debt instruments with interest rates that are subject to periodic adjustment based on an index or formula with original contractual maturities greater than one year. Senior floating rate debt takes priority over other debt instruments sold by the company. In the event the company goes bankrupt, senior floating rate debt holders receive priority for repayment prior to junior or unsecured general creditors. Measurement Input, Default Rate [Member] Measurement Input, Default Rate [Member] Fair Value Inputs, Quantitative Information [Line Items] Trading securities Debt Securities, Trading, and Equity Securities, FV-NI Available-for-sale securities Available-for-sale Securities Net derivatives Derivative Asset, Fair Value, Amount Not Offset Against Collateral Long-term debt Long-term Debt, Fair Value Spread (bps) Entities [Table] Common Stock [Member] Common Stock [Member] Entity Information [Line Items] Entity Information [Line Items] Document Type Document Annual Report Document Annual Report Document Period End Date Document Transition Report Document Transition Report Entity File Number Entity File Number Entity Tax Identification Number Entity Tax Identification Number Entity Registrant Name Entity Central Index Key Current Fiscal Year End Date Entity Filer Category Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Entity Small Business Entity Small Business Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Entity Public Float Entity Public Float Entity Well-known Seasoned Issuer Entity Voluntary Filers Entity Shell Company Entity Shell Company Entity Current Reporting Status Entity Interactive Data Current Entity Interactive Data Current Entity Address, Address Line One Entity Address, Address Line One City Area Code City Area Code Local Phone Number Local Phone Number Entity Address, City or Town Entity Address, City or Town Entity Address, State or Province Entity Address, State or Province Entity Address, State or Province Entity Address, Postal Zip Code Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Entity Emerging Growth Company Entity Emerging Growth Company Amendment Flag Amendment Flag Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] Unrecognized tax benefits as of January 1 Unrecognized Tax Benefits Unrecognized tax benefits as of December 31 Unrecognized Tax Benefit Resulting in Tax Credits and/or Net Operating Loss Carryforward Unrecognized Tax Benefit Resulting in Tax Credits and/or Net Operating Loss Carryforward Amount of an unrecognized tax benefit that is directly related to a position taken in a tax year that results in a tax credit and/or net operating loss carryforward. This amount is presented as a reduction of the related deferred tax asset in the balance sheet if that deferred tax asset is not used. This amount is presented separately from the deferred tax asset for a tax credit and/or net operating loss carryforward if this unrelated tax benefit is associated with a different tax position. Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions Regulatory Capital Requirements Regulatory Capital Requirements under Banking Regulations [Text Block] Segment Results [Table] Schedule of Segment Reporting Information, by Segment [Table] Total Results [Domain] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Fee and other income Noninterest Income, Other Net revenues Revenues, Net of Interest Expense Investment gains, net Fair value losses, net Administrative expenses Benefit for credit losses Foreclosed property income (expense) Credit-related income (expense) Credit-related income (expense) Total credit-related income and expenses, including benefit (provision) for credit losses and foreclosed property income and expenses. Other expenses, net Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Offsetting [Abstract] Derivative [Table] Derivative [Table] Cash and Cash Equivalents [Member] Cash and Cash Equivalents [Member] Derivative [Line Items] Derivative [Line Items] Fair value of non-cash collateral we pledged Financial Instruments Owned and Pledged as Collateral, Amount Eligible to be Repledged by Counterparty Fair value of non-cash collateral received Securities Received as Collateral Fair value of non-cash collateral received that could be sold or repledged Fair Value of Securities Received as Collateral that Can be Resold or Repledged Fair value of underlying collateral that was sold or repledged Fair Value of Securities Received as Collateral that Have Been Resold or Repledged Derivative assets not subject to an enforceable master netting arrangement Derivative Asset, Not Subject to Master Netting Arrangement Derivative liabilities not subject to an enforceable master netting arrangement Derivative Liability, Not Subject to Master Netting Arrangement Securities purchased under agreements to resell Securities Purchased under Agreements to Resell Financing Receivable, Held-for-investment Policy Financing Receivable, Held-for-investment [Policy Text Block] Financing Receivable, Held-for-sale Policy Financing Receivable, Held-for-sale [Policy Text Block] Troubled Debt Restructurings Policy Troubled Debt Restructuring [Policy Text Block] Derivative Instruments and Hedging Activities Disclosure [Abstract] Derivative Instruments Derivative Instruments and Hedging Activities Disclosure [Text Block] Deferred tax assets: Deferred Tax Assets, Gross [Abstract] Mortgage and mortgage-related assets Mortgage And Mortgage Related Assets Including Acquired Credit Impaired Loans Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences derived from fair value adjustments, cost basis adjustments and impairments of loans and securities. Allowance for loan losses and basis in acquired property, net Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Provision for Loan Losses Debt and derivative instruments Deferred Tax Assets, Derivative Instruments Partnership credits Deferred Tax Assets, Tax Credit Carryforwards, Other Partnership and other equity investments Deferred Tax Assets, Equity Method Investments Deferred Tax Assets, Investments Deferred Tax Assets, Investments Other, net Deferred Tax Assets, Other Total deferred tax assets Deferred Tax Assets, Gross Deferred tax liabilities: Deferred Tax Liabilities, Gross [Abstract] Unrealized gains on AFS securities, net Deferred Tax Assets, Unrealized Gains on Available-for-Sale Securities, Gross Amount of deferred tax liability attributable to taxable temporary differences from unrealized gains on available-for-sale securities. Deferred Tax Liabilities, Other Deferred Tax Liabilities, Other Total deferred tax liabilities Deferred Tax Liabilities, Gross Net deferred tax assets Deferred Tax Assets, Net Schedule of Short-Term Borrowings [Table] Schedule of Short-term Debt [Table] Short-Term Debt, Type [Axis] Short-term Debt, Type [Axis] Short-Term Debt, Type [Domain] Short-term Debt, Type [Domain] Federal Funds Purchased and Securities Sold under Agreements to Repurchase [Member] Federal Funds Purchased and Securities Sold under Agreements to Repurchase [Member] Line of Credit [Member] Line of Credit [Member] Short-Term Debt [Line Items] Short-term Debt [Line Items] Federal Funds Purchased and Securities Sold under Agreements to Repurchase Federal Funds Purchased and Securities Sold under Agreements to Repurchase Debt, Weighted Average Interest Rate Debt, Weighted Average Interest Rate Short-term debt, outstanding Short-term Debt Short-term debt, weighted-average interest rate Short-term Debt, Weighted Average Interest Rate, at Point in Time Line of credit maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Derivatives, Offsetting Policy Derivatives, Offsetting Fair Value Amounts, Policy [Policy Text Block] Financial Guarantees and Maximum Recovery [Table] Financial Guarantees and Maximum Recovery [Table] Financial Guarantees and Maximum Recovery [Table] Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] Unconsolidated VIEs [Member] Other guaranty arrangements [Member] Guarantee Type, Other [Member] Financial Guarantees and Maximum Recovery [Line Items] Financial Guarantees and Maximum Recovery [Line Items] [Line Items] for Financial Guarantees and Maximum Recovery [Table] Contractual terms of our guarantees Contractual terms of our guarantees1 Represents the original contractual term of guarantees. Maximum exposure Guarantor Obligations, Maximum Exposure, Undiscounted Guaranty obligation Guarantor Obligations, Current Carrying Value Maximum recovery Maximum Recovery Represents the maximum amount we could recover through available credit enhancements and recourse with third parties on guarantees recognized in our on and off balance sheets. Recoverability of such credit enhancements and recourse is subject to, among other factors, our mortgage insurers' and financial guarantors' ability to meet their obligations to us. Freddie Mac collateral included in Fannie Mae commingled security Freddie Mac collateral included in Fannie Mae commingled security Portion of Freddie Mac securities backing commingled Fannie Mae-issued structured securities. Principles of Consolidation Policy Consolidation, Policy [Policy Text Block] Transfers and Servicing of Financial Assets Policy Transfers and Servicing of Financial Assets, Policy [Policy Text Block] Schedule of Variable Interest Entities [Table] Schedule of Variable Interest Entities [Table] Consolidated VIEs [Member] Investment Type [Axis] Investment Type [Axis] Investments [Domain] Investments [Domain] Partnership Interest [Member] Partnership Interest [Member] Debt Securities [Member] Debt Securities [Member] Fannie Mae Securities [Member] Non-Fannie Mae Securities [Member] Variable Interest Entities [Line Items] Variable Interest Entity [Line Items] Available-for-sale securities Debt Securities, Available-for-sale Other assets Other Assets Other liabilities Other Liabilities Net carrying amount Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net Maximum exposure to loss Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount Total unconsolidated assets Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets Unpaid principal balance of mortgage loans Mortgage Loans on Real Estate, Unpaid Principal Balance Represents principal amount outstanding of mortgage loans. Commitments and Contingencies Policy Commitments and Contingencies, Policy [Policy Text Block] Loan and Mortgage Related Securities Commitments Policy Loan and Mortgage-related Securities Commitments Policy [Policy Text Block] Disclosure of accounting policy for loan commitments and mortgage-related securities accounted for as derivatives, including the methods and assumptions used to estimate fair value. Netting Arrangements Netting Arrangements [Text Block] The entire disclosure for balance sheet offsetting/netting arrangements. Statement of Financial Position [Abstract] ASSETS Assets [Abstract] Restricted cash (includes $33,294 and $17,849, respectively, related to consolidated trusts) Restricted Cash and Cash Equivalents Investments in securities: Marketable Securities [Abstract] Available-for-sale, at fair value Mortgage loans: Mortgage Loans on Real Estate, Commercial and Consumer, Net, (Investment Based Operations Presentation) [Abstract] Loans held for investment, at amortized cost of consolidated trusts (includes $12,057 and $14,075, respectively, at fair value) Accrued interest receivable, net (includes $8,172 and $7,928, respectively, related to consolidated trusts) Interest Receivable Liabilities: Liabilities [Abstract] Accrued interest payable (includes $9,361 and $9,133, respectively, related to consolidated trusts) Interest Payable Debt at fair value Other liabilities (includes $376 and $356, respectively, related to consolidated trusts) Fannie Mae stockholders’ equity: Stockholders' Equity Attributable to Parent [Abstract] Senior preferred stock, 1,000,000 shares issued Senior Preferred Stock Issued Shares Aggregate number of shares of senior preferred stock issued to stockholders Senior preferred stock, 1,000,000 shares outstanding Senior Preferred Stock Shares Outstanding Aggregate number of shares of senior preferred stock outstanding Preferred stock, 700,000,000 shares are authorized Preferred Stock, Shares Authorized Preferred stock, 555,374,922 shares issued Preferred Stock, Shares Issued Preferred stock, 555,374,922 shares outstanding Preferred Stock, Shares Outstanding Common stock, no par value, no maximum authorization, 1,308,762,703 shares issued Common Stock, Shares, Issued Common stock, no par value, no maximum authorization, 1,158,087,567 and 1,158,082,750 shares outstanding, respectively Common Stock, Shares, Outstanding Treasury stock, at cost, 150,675,136 and 150,679,953 shares, respectively Treasury Stock, Shares Security Owned and Pledged as Collateral, Fair Value Security Owned and Pledged as Collateral, Fair Value Gross realized gains Available-for-sale Securities, Gross Realized Gains Proceeds from Sale of Available-for-sale Securities Proceeds from Sale of Available-for-sale Securities Offsetting [Table] Offsetting [Table] Disclosure of information about derivative, financial assets and liabilities that are subject to offsetting, including enforceable master netting arrangements. Transaction Type [Axis] Transaction Type [Axis] Transaction [Domain] Transaction [Domain] Over the Counter [Member] Over the Counter [Member] Exchange Cleared [Member] Exchange Cleared [Member] Derivative Instrument [Axis] Derivative Contract [Domain] Risk management derivatives Interest Rate Contract [Member] Offsetting Assets [Line Items] Offsetting Assets [Line Items] Financial Instruments Owned and Pledged as Collateral, Amount Eligible to be Repledged by Counterparty Assets: Derivative assets, gross amount Derivative Asset, Fair Value, Gross Asset Derivative asset, gross amount offset Derivative Asset, Fair Value, Gross Liability Derivative assets, net amount presented in our consolidated balance sheets Derivative assets, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial instruments Derivative Asset, Not Offset, Policy Election Deduction Derivative assets, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral Derivative, Collateral, Obligation to Return Securities Derivative assets, net amount Derivative Asset, Fair Value, Amount Offset Against Collateral Securities purchased under agreements to resell, or similar arrangements, gross amount Securities Purchased under Agreements to Resell, Gross Securities purchased under agreements to resell or similar arrangements, gross amount offset Securities Purchased under Agreements to Resell, Liability Securities purchased under agreements to resell or similar arrangements, net amount presented in our consolidated balance sheets Securities Purchased under Agreements to Resell, Not Subject to Master Netting Arrangement Securities purchased under agreements to resell, under master netting arrangement, amounts not offset in our consolidated balance sheets, financial instruments Securities Purchased under Agreements to Resell, Not Offset, Policy Election Deduction Securities purchased under agreements to resell or similar arrangements, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral Securities Purchased under Agreements to Resell, Collateral, Obligation to Return Securities Securities purchased under agreements to resell or similar arrangements, net amount Securities Purchased under Agreements to Resell, Amount Offset Against Collateral Total assets, gross amount Derivative Asset, Securities Purchased under Agreements to Resell, Securities Borrowed, Gross Total assets, gross amount offset Derivative Asset, Securities Purchased under Agreements to Resell, Securities Borrowed, Liability Total assets, net amount presented in the consolidated balance sheets Derivative Asset, Securities Purchased under Agreements to Resell, Securities Borrowed, Subject to Master Netting Arrangement Amount, after the effects of master netting arrangements, of derivative assets, securities purchased under agreements to resell and securities borrowed. Includes assets subject to a master netting arrangement only. Total assets, under the master netting arrangements, not offset in our consolidated balance sheets, financial instruments Derivative Asset, Securities Purchased Under Agreements to Resell, Subject to Master Netting Arrangement, Not Offset, Financial Instruments Amount of derivative assets and securities purchased under agreements to resell, subject to master netting arrangement which have not been offset that are off-balance sheet arrangements. Total assets, under master netting arrangements, not offset in our consolidated balance sheets, collateral Derivative Asset, Securities Purchased under Agreements to Resell, Securities Borrowed, Collateral, Obligation to Return Securities Total assets, net amount Derivative Asset, Securities Purchased under Agreements to Resell, Securities Borrowed, Amount Offset Against Collateral Derivative liabilities, gross amount Derivative Liability, Fair Value, Gross Liability Derivative liabilities, gross amount offset Derivative Liability, Fair Value, Gross Asset Derivative liabilities, net amount presented in our consolidated balance sheets Derivative Liability, Fair Value, Amount Not Offset Against Collateral Derivative liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial instruments Derivative Liability, Not Offset, Policy Election Deduction Derivative liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral Derivative, Collateral, Right to Reclaim Securities Derivative liabilities, net amount Derivative Liability, Fair Value, Amount Offset Against Collateral Securities Sold under Agreements to Repurchase, Gross Securities Sold under Agreements to Repurchase, Gross Securities Sold under Agreements to Repurchase, Not Subject to Master Netting Arrangement Securities Sold under Agreements to Repurchase, Not Subject to Master Netting Arrangement Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Securities Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Securities Securities Sold under Agreements to Repurchase, Amount Offset Against Collateral Securities Sold under Agreements to Repurchase, Amount Offset Against Collateral Total liabilities, gross amount Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned, Gross Total liabilities, gross amount offset Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned, Asset Total liabilities, net amount presented in our consolidated balance sheets Derivative Liability, Securities Sold under Agreements to Resell, Securities Loaned, Subject to Master Netting Arrangements Amount, after the effects of master netting arrangements, of derivative liabilities, securities sold under agreements to repurchase and securities loaned. Includes liabilities subject to a master netting arrangement. Total liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, financial statements Derivative Liability, Securities Sold under Agreements to Resell, Subject to Master Netting Arrangement, Not Offset, Financial Instruments Amount of derivative liabilities and securities sold under agreements to repurchase, subject to a master netting arrangement that are not offset which are off-balance sheet arrangements. Total liabilities, under master netting arrangements, amounts not offset in our consolidated balance sheets, collateral Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned, Collateral, Right to Reclaim Securities Total liabilities, net amount Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned, Amount Offset Against Collateral Securities Received as Collateral Fair Value of Securities Received as Collateral that Can be Resold or Repledged Fair Value of Securities Received as Collateral that Have Been Resold or Repledged Derivative Asset, Not Subject to Master Netting Arrangement Derivative Liability, Not Subject to Master Netting Arrangement Securities Purchased under Agreements to Resell Total assets by segment Reconciliation of Assets from Segment to Consolidated [Table Text Block] Segment results Schedule of Segment Reporting Information, by Segment [Table Text Block] Accounting Policies [Abstract] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] Series 2008-2 Senior Preferred Stock [Member] Series 2008-2 Senior Preferred Stock [Member] Series 2008-2 Senior Preferred Stock -issued on September 8, 2008 one million of variable liquidation preference senior preferred stock with an aggregate stated value of $1.0 billion agreement with Treasury. Senior preferred stock ranks senior to all other series of preferred stock as both dividends and distribution upon dissolution, liquidation or winding up the company. Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Early Lender Funding Advances, Maximum Term Early Lender Funding Advances, Maximum Term Represent the maximum number of days the lenders have when we provide early funding to lenders for loans that they will subsequently either sell to us or securitize into a Fannie Mae MBS that they will deliver to us. Weighted Average Number of Shares, Contingently Issuable Weighted Average Number of Shares, Contingently Issuable Incremental Common Shares Attributable to Dilutive Effect of Conversion of Preferred Stock Incremental Common Shares Attributable to Dilutive Effect of Conversion of Preferred Stock Stock Issued During Period, Shares, New Issues Stock Issued During Period, Shares, New Issues Capital Reserve Amount Fiscal Year Senior Preferred Stock Purchase Agreement September 2019 Amendment Capital Reserve Amount Fiscal Year Senior Preferred Stock Purchase Agreement September 2019 Amendment Represent the amount of increase in capital the company is allowed to reserve for the fiscal year per latest amended senior preferred stock purchase agreement between the company and US Treasury Aggregate liquidation preference of senior preferred stock Aggregate Liquidation Preference of Senior Preferred Stock Represents the aggregated liquidation preference of senior preferred stock issued and outstanding held by U.S. Treasury. Comprehensive Income (Loss), Net of Tax, Attributable to Parent Comprehensive Income (Loss), Net of Tax, Attributable to Parent Percentage Of Common Shares Attributable to Warrants Issued to Treasury as Percentage to Total Diluted Common Shares Percentage Of Common Shares Attributable to Warrants Issued to Treasury as Percentage to Total Diluted Common Shares Represents a percentage of common shares warrants issued to U.S. Treasury as a percentage of the total number of the company's diluted common shares. Common stock warrant exercise price per share Class of Warrant or Right, Exercise Price of Warrants or Rights Fair value of the warrant at issuance Adjustments to Additional Paid in Capital, Warrant Issued Fair Value Measurements, Recurring [Table] Fair Value, Recurring and Nonrecurring [Table] Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] Fair Value, Inputs, Level 1 [Member] Swaps [Member] Swap [Member] Swaptions [Member] Swaption [Member] Credit enhancement derivatives Other Contract [Member] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Cash and Cash Equivalents, Fair Value Disclosure Cash and Cash Equivalents, Fair Value Disclosure Assets [Abstract] Assets, Fair Value Disclosure [Abstract] Other assets [Abstract] Other Assets [Abstract] Derivative assets at fair value Derivative Asset Total assets at fair value Liabilities [Abstract] Liabilities, Fair Value Disclosure [Abstract] Long-term debt, fair value Other liabilities [Abstract] Other Liabilities [Abstract] Derivatives liabilities at fair value Derivative Liability Derivative liabilities, gross amount offset Total liabilities at fair value Financial and Nonfinancial Liabilities, Fair Value Disclosure Unconsolidated Variable Interest Entities Schedule of Variable Interest Entities [Table Text Block] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Debt Instrument, Redemption, Period [Axis] Debt Instrument, Redemption, Period [Axis] Debt Instrument, Redemption, Period [Domain] Debt Instrument, Redemption, Period [Domain] Earlier of Contractual Maturity or Next Call Date [Member] Earlier of Contractual Maturity or Next Call Date [Member] Long-term debt shown as the earlier of maturity date or next call date. Zero-Coupon Debt [Member] Zero-Coupon Debt [Member] Represents a debt security that doesn't pay interest (a coupon)but is traded/sold at a deep discount, rendering profit at maturity when the bond is redeemed for its full face value. Callable [Member] Callable [Member] A debt security whose issuer has the right to redeem the security at a specified price on or after a specified date, prior to its stated final maturity. Long-Term Debt [Line Items] Debt Instrument [Line Items] Face amount Debt Instrument, Face Amount Effective interest rate Debt Instrument, Interest Rate, Effective Percentage Outstanding debt Long-term Debt, Gross Long-Term Debt by Year of Maturity [Abstract] Long-term Debt, Fiscal Year Maturity [Abstract] 2020 Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months 2021 Long-term Debt, Maturities, Repayments of Principal in Year Two 2022 Long-term Debt, Maturities, Repayments of Principal in Year Three 2023 Long-term Debt, Maturities, Repayments of Principal in Year Four 2024 Long-term Debt, Maturities, Repayments of Principal in Year Five Thereafter Long-term Debt, Maturities, Repayments of Principal after Year Five Total long-term debt Long-term Debt Net unamortized discount, fair value adjustments and other cost basis adjustments Debt Instrument, Unamortized Discount (Premium), Net Financial Guarantees and Maximum Recovery Financial Guarantees and Maximum Recovery [Table Text Block] Tabular disclosure of financial guarantees and the maximum recovery. Unrecognized Tax Benefits, Period Increase (Decrease) Unrecognized Tax Benefits, Period Increase (Decrease) Income Tax Provision (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract] Effective Income Tax Rate Reconciliation, Amount [Abstract] Current income tax benefit (provision) Current Income Tax Expense (Benefit) Deferred income tax provision Deferred Income Tax Expense (Benefit) Provision for federal income taxes Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract] Effective Income Tax Rate Reconciliation, Percent [Abstract] Equity investments in affordable housing projects Effective Income Tax Rate Reconciliation, Tax Credit, Investment, Percent Effect of corporate tax rate change Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent Effective Income Tax Rate Reconciliation, Tax Settlement, Percent Effective Income Tax Rate Reconciliation, Tax Settlement, Percent Effective Income Tax Rate Reconciliation, Other Adjustments, Percent Effective Income Tax Rate Reconciliation, Other Adjustments, Percent Effective tax rate Effective Income Tax Rate Reconciliation, Percent Statement of Stockholders' Equity [Abstract] Changes in net unrealized gains on available-for-sale securities, net of tax Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax Reclassification adjustment for gains included in net loss, net of tax Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Plan Amendments, Tax Effect Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Plan Amendments, Tax Effect Senior Fixed [Member] Senior Fixed Debt [Member] Senior fixed rate debt instruments with an original contractual maturity of greater than one year. Senior fixed rate debt takes priority over other debt securities sold by the company. In the event the company goes bankrupt, senior fixed rate debt holders receive priority for repayment prior to junior or unsecured general creditors. Senior fixed benchmark notes and bonds [Member] Senior Fixed Benchmark Notes and Bonds [Member] Senior fixed benchmark bonds represent noncallable fixed rate debt instruments with original contractual maturities greater than ten years. Senior fixed benchmark notes are regularly issued non-callable fixed rate debt instruments with original maturities from two to ten years. Senior fixed rate debt takes priority over other debt instruments sold by the company. In the event the company goes bankrupt, senior fixed rate debt holders receive priority for repayment prior to junior or unsecured general creditors. Senior fixed medium-term notes [Member] Senior Fixed Medium-term Notes [Member] Senior fixed medium-term notes represent debt instruments with original contractual maturities ranging from one to ten years, excluding zero-coupon debt. Senior fixed rate debt takes priority over other debt instruments sold by the company. In the event the company goes bankrupt, senior fixed rate debt holders receive priority for repayment prior to junior or unsecured general creditors. Senior fixed other debt [Member] Senior Fixed Other Debt [Member] Senior fixed other represent debt instruments with original contractual maturities greater than one year that are not included in other senior fixed rate debt categories. Includes a portion of structured debt instruments that is reported at fair value. Senior fixed rate debt takes priority over other debt instruments sold by the company. In the event the company goes bankrupt, senior fixed rate debt holders receive priority for repayment prior to junior or unsecured general creditors. Senior floating medium-term notes [Member] Senior Floating Medium-term Notes [Member] Senior floating medium-term notes with interest rates that are subject to adjustment represent debt instruments with original contractual maturity dates ranging from one to ten years, excluding zero-coupon debt. Senior floating debt takes priority over other debt instruments sold by the company. In the event the company goes bankrupt, senior floating debt holders receive priority for repayment prior to junior or unsecured general creditors. Senior floating Connecticut Avenue Securities [Member] Senior Floating Connecticut Avenue Security [Member] Senior floating Connecticut Avenue Securities represent credit risk sharing securities, in which a portion of the credit risk on the underlying mortgage loans is transferred to the investors in these securities in exchange for sharing a portion of the guaranty fee payments. Fannie Mae has elected to account for these securities using the fair value option. Senior floating other debt [Member] Senior Floating Other Debt [Member] Senior floating other with interest rates that are subject to adjustment represents debt instruments with original contractual maturities greater than one year that is not included in other senior floating rate debt categories. Includes a portion of structured debt instruments that is reported at fair value. Senior floating debt takes priority over other debt instruments sold by the company. In the event the company goes bankrupt, senior floating debt holders receive priority for repayment prior to junior or unsecured general creditors. Subordinated debentures [Member] Subordinated Debt [Member] Secured borrowings [Member] Secured borrowings [Member] Represents remaining liability for transfer of financial assets from our consolidated balance sheet that did not qualify as a sale. Medium-term Notes Original Contractual Maturity 1 Medium-term Notes Original Contractual Maturity 1 Represents long-term medium-term notes with original contractual maturities greater than one year and up to 10 years. Long-term debt, outstanding Long-term debt, weighted-average interest rate Long-term Debt, Weighted Average Interest Rate, at Point in Time Long-term debt, original contractual maturity greater than 10 years Long-term debt, original contractual maturity greater than 10 years Represents long-term original contractual maturity greater than 10 years Short-Term Debt Schedule of Short-term Debt [Table Text Block] Long-Term Debt Schedule of Long-term Debt Instruments [Table Text Block] Long-Term Debt by Year of Maturity Schedule of Maturities of Long-term Debt [Table Text Block] Receivables [Abstract] Allowance for loan losses for individually impaired loans Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment Allowance for loan losses for collectively reserved loans Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment Total allowance for loan losses Allowance for Loan and Lease Losses, Real Estate Recorded investment in individually impaired loans Financing Receivable, Individually Evaluated for Impairment Recorded investment in collectively reserved loans Financing Receivable, Collectively Evaluated for Impairment Total recorded investment in loans Earnings Per Share, Policy [Policy Text Block] Earnings Per Share, Policy [Policy Text Block] Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Individually impaired loans with related allowance recorded: unpaid principal balance Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance Individually impaired loans with related allowance recorded: total recorded investment Impaired Financing Receivable, with Related Allowance, Recorded Investment Related allowance for loan losses Impaired Financing Receivable, Related Allowance Individually impaired loans with no related allowance recorded: unpaid principal balance Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance Individually impaired loans with no related allowance recorded: total recorded investment Impaired Financing Receivable, with No Related Allowance, Recorded Investment Total individually impaired loans: unpaid principal balance Impaired Financing Receivable, Unpaid Principal Balance Total individually impaired loans: total recorded investment Impaired Financing Receivable, Recorded Investment Troubled debt restructuring recorded investment Financing Receivable, Troubled Debt Restructuring Investments In Trading Securities Debt Securities, Trading, and Equity Securities, FV-NI [Table Text Block] Schedule of Trading Securities Gains (Losses), Net Schedule of Trading Securities Gains (Losses), Net [Table Text Block] Represents a tabular disclosure of net trading gains and losses that have been recognized in earnings (statement of operations and comprehensive income) and net trading gains and losses recorded in the period related to securities held at period end. Schedule of Available-for-sale Securities Realized Gain (Loss) Schedule of Realized Gain (Loss) [Table Text Block] Schedule of Available-for-sale Securities Reconciliation Schedule of Available-for-sale Securities Reconciliation [Table Text Block] Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Table Text Block] Investments Classified by Contractual Maturity Date Investments Classified by Contractual Maturity Date [Table Text Block] Schedule of Accumulated Other Comprehensive Income (Loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Purchase Obligation Rent expenses for operating leases Selected Quarterly Financial Information (Unaudited) Quarterly Financial Information [Text Block] Derivative Instruments, Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk [Table] Derivative Instruments, Gain (Loss) [Table] Pay-fixed swap Pay-fixed Swap [Member] Represents an agreement under which we pay a predetermined fixed rate of interest based upon a set notional principal amount and receive a variable interest payment based upon a stated index, with the index resetting at regular intervals over a specified period of time. These contracts generally increase in value as interest rates rise and decrease in value interest rates fall. Receive-fixed Swap Receive-fixed Swap [Member] Represents an agreement under which we make a variable interest payment based upon a stated index, with the index resetting at regular intervals, and receive a predetermined fixed rate of interest based upon a set notional amount and over a specified period of time. These contracts generally increase in value as interest rates fall and decrease in value interest rates rise. Basis swap Basis Swap [Member] Foreign currency swap Currency Swap [Member] Pay-fixed swaption Pay-fixed Swaption [Member] Represents an option on interest rate pay-fixed swaps in the form of contracts granting an option to one party and creating a corresponding commitment from the counterparty to enter into specified interest rate pay-fixed swaps in the future. Swaptions are traded in the over-the-counter market and not through an exchange. Receive-fixed swaption Receive-fixed Swaption [Member] Represents an option on interest rate received-fixed swaps in the form of contracts granting an option to one party and creating a corresponding commitment from the counterparty to enter into specified interest rate receive-fixed swaps in the future. Swaptions are traded in the over-the-counter market and not through an exchange. Futures Future [Member] Derivative Instruments, Gain (Loss) [Line Items] Derivative Instruments, Gain (Loss) [Line Items] Derivative fair value gains (losses), net Derivative, Gain (Loss) on Derivative, Net Net accrual of periodic settlements Fair Value of Financial Instruments [Table] Fair Value, by Balance Sheet Grouping [Table] Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement [Member] Portion at Fair Value Measurement [Member] Carrying Value [Member] Reported Value Measurement [Member] Estimate of Fair Value Measurement [Member] Estimate of Fair Value Measurement [Member] Financial Instruments [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Financial assets [Abstract] Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract] Cash and cash equivalents and restricted cash Cash, Cash Equivalents, and Restricted Cash, Fair Value Disclosure This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Company may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. The carrying amounts of cash and cash equivalent items which are restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits; however, time deposits and short-term certificates of deposit are not generally included in legally restricted deposits. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. This element is for unclassified presentations; for classified presentations there is a separate and distinct element. Federal funds sold and securities purchased under agreements to resell or similar arrangements Federal Funds Sold and Securities Borrowed or Purchased under Agreements to Resell, Fair Value Disclosure Mortgage loans held for sale Advances to lenders Advances to Lenders, Fair Value Disclosure Advance to lenders represent payments of cash in exchange for the receipt of mortgage loans from lenders in a transfer that is accounted for as a secured lending arrangement valued at fair value. Netting adjustment Guaranty assets and buy-ups Guaranty Assets and Buy-ups, Fair Value Disclosure Represent the present value of expected future cash flows of the underlying off balance sheet guaranty and buy-up assets valued at fair value. Buy-ups refer to upfront payments we make to lenders to adjust the monthly contractual guaranty fee rate on a Fannie Mae MBS so that the pass-through coupon rate on the MBS is in a more easily tradable increment of a whole or half percent. Federal Funds Purchased and Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure Federal Funds Purchased and Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure Financial liabilities [Abstract] Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract] Short-term debt Short-term Debt, Fair Value Long-term debt Netting adjustment Guaranty obligations Guarantees, Fair Value Disclosure Schedule of Other than Temporary Impairment, Credit Losses Recognized in Earnings [Table] Schedule of Other than Temporary Impairment, Credit Losses Recognized in Earnings [Table] Debt Security Category [Axis] Debt Security Category [Axis] Other than Temporary Impairment, Credit Losses Recognized in Earnings, Categories of Investments [Domain] Other than Temporary Impairment, Credit Losses Recognized in Earnings, Categories of Investments [Domain] Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items] Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items] Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held Accumulated Other Comprehensive Income (Loss), Net of Tax, Available-for-sale Securities, Other-than-temporary Impairment not Recorded Accumulated Other Comprehensive Income (Loss), Net of Tax, Available-for-sale Gain (Loss), Other-than-temporary Impairment Recorded Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax Accumulated Other Comprehensive Income (Loss), Net of Tax Basis of Accounting, Policy [Policy Text Block] Basis of Accounting, Policy [Policy Text Block] Single-Family Guaranty Fees 10 Basis Points Increase due to the Temporary Payroll Tax Cut Continuation Act of 2011 Provision Policy Single-Family Guaranty Fees 10 Basis Points Increase due to a provision stated in the Temporary Payroll Tax Cut Continuation Act of 2011 [Policy Text Block] Disclosure of accounting policy with regard to the 10 basis points increase in guaranty fees on all single-family residential mortgage securitization which was enacted by the Congress as a part of the Temporary Payroll Tax Cut Continuation Act of 2011 and remit this increase to Treasury. Use of Estimates Policy Use of Estimates, Policy [Policy Text Block] Consolidation, Variable Interest Entity Policy Consolidation, Variable Interest Entity, Policy [Policy Text Block] Cash and Cash Equivalents Policy Cash and Cash Equivalents, Policy [Policy Text Block] Nonaccrual Loans Policy Loans and Leases Receivable, Nonaccrual Loan and Lease Status, Policy [Policy Text Block] Allowance for Loan Losses Policy Loans and Leases Receivable, Allowance for Loan Losses Policy [Policy Text Block] Impaired Financing Receivable Policy Impaired Financing Receivable, Policy [Policy Text Block] Advances to Lenders Policy Advances to Lenders [Policy Text Block] Disclosure of accounting policy for cash payments made in exchange for the receipt of mortgage loans from lenders in a transfer that is accounted for as a secured lending arrangement. These transfers primarily occur when we provide early funding to lenders for loans that they will subsequently either sell to us or securitize into a Fannie Mae MBS that they will deliver to us. We individually negotiate early lender funding advances with our lender customers. Early lender funding advances have terms up to 60 days and earn a short-term market rate of interest. Financing Receivable, Held-for-investment, Foreclosed Asset Policy Financing Receivable, Held-for-investment, Foreclosed Asset [Policy Text Block] Commitments to Purchase and Sell Mortgage Loans and Securities Policy Commitments to Purchase and Sell Mortgage Loans and Securities [Policy Text Block] Disclosure of accounting policy for commitments to purchase and sell mortgage- backed securities and to purchase single-family and multifamily mortgage loans. Derivatives Policy Derivatives, Policy [Policy Text Block] Derivatives, Offsetting Fair Value Amounts Policy Derivatives, Embedded Derivatives Policy Derivatives, Embedded Derivatives [Policy Text Block] Repurchase Agreements, Collateral Policy Repurchase Agreements, Collateral, Policy [Policy Text Block] Debt Policy Debt, Policy [Policy Text Block] Interest Expense Policy Interest Expense, Policy [Policy Text Block] Income Tax Policy Income Tax, Policy [Policy Text Block] Income Tax Uncertainties Policy Income Tax Uncertainties, Policy [Policy Text Block] Earnings Per Share Policy New Accounting Pronouncements Policy New Accounting Pronouncements, Policy [Policy Text Block] Loans in Mortgage Portfolio [Table] Loans In Mortgage Portfolio [Table] Schedule detailing Single-family and Multifamily mortgage loans, including loans held for investment and loans held for sale of Fannie Mae and Consolidated Trusts, as of the end of the period. In addition, we report the related allowance for loan losses for loans held for investment as of the end of the period. Loans in Mortgage Portfolio [Line Items] Loans In Mortgage Portfolio [Line Items] Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. Cost basis and fair value adjustments, net Mortgage Loans, Cost Basis and Fair Value Adjustments, Net Represents premiums over or discounts from face amounts of loans that are being amortized into income as an adjustment to yield and fair value adjustments. Allowance for loan losses for loans held for investment Total mortgage loans Loans and Leases Receivable, Net Amount Carrying value of loans redesignated from HFI to HFS Financing Receivable, Reclassification to Held-for-sale Carrying value of loans redesignated from HFS to HFI Financing Receivable, Reclassification to Held-for-investment The amount of financing receivable to held-for-investment during the reporting period. Sale of loans, unpaid principal balance Financing Receivable, Sale Realized gains on sales of mortgage loans Gain (Loss) on Sale of Mortgage Loans Recorded investment of single-family mortgage loans referred to foreclosure Mortgage Loans in Process of Foreclosure, Amount Notional and Fair Value Position Schedule of Derivative Instruments [Table Text Block] Fair Value Gain (Loss), Net Derivative Instruments, Gain (Loss) [Table Text Block] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Federal funds sold and securities purchased under agreements to resell or similar arrangements Federal Funds Sold and Securities Purchased under Agreements to Resell Trading, at fair value (includes $3,037 and $3,061, respectively, pledged as collateral) Total investments in securities Marketable Securities Loans Receivable Held-for-sale, Amount Loans Receivable Held-for-sale, Amount Financing Receivable, before Allowance for Credit Loss (includes $7,825 and $8,922, respectively, at fair value) Financing Receivable, before Allowance for Credit Loss Allowance for loan losses Total loans held for investment, net of allowance Mortgage Loans on Real Estate, Commercial and Consumer, Net Deferred tax assets, net Deferred Tax Assets, Net of Valuation Allowance Acquired property, net Real Estate Acquired Through Foreclosure Other assets Total assets LIABILITIES AND EQUITY Liabilities and Equity [Abstract] Debt (includes $5,687 and $6,826, respectively, of debt of Fannie Mae and $21,880 and $23,753, respectively, of debt of consolidated trusts, at fair value) Debt and Lease Obligation Total liabilities Liabilities Commitments and contingencies (Note 16) Commitments and Contingencies Equity: Senior preferred stock (liquidation preference of $131,178 and $123,836, respectively) Senior Preferred Stock Value Aggregate stated value of senior preferred stock issued and outstanding Preferred stock, 700,000,000 shares are authorized—555,374,922 shares issued and outstanding Preferred Stock, Value, Issued Common stock, no par value, no maximum authorization—1,308,762,703 shares issued and 1,158,087,567 shares outstanding Common Stock, Value, Issued Accumulated deficit Retained Earnings (Accumulated Deficit) Accumulated other comprehensive income Treasury stock, at cost, 150,675,136 shares Treasury Stock, Value Total liabilities and equity Liabilities and Equity Types of Vie [Abstract] Types of Vie [Abstract] Variable Interest Entity [Line Items] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Net trading gains (losses) Net Realized and Unrealized Gain (Loss) on Trading Securities Net trading gains (losses) recognized in the period related to securities still held at period end Trading Securities, Change in Unrealized Holding Gain (Loss) Schedule of Assumptions for Fair Value as of Balance Sheet Date of Assets or Liabilities that relate to Transferor's Continuing Involvement [Table] Qualitative and Quantitative Information, Transferor's Continuing Involvement [Table] Qualitative and Quantitative Information, Transferor's Continuing Involvement, Transferred Financial Assets, by Transfer or Transferee [Axis] Qualitative and Quantitative Information, Transferor's Continuing Involvement, Transferred Financial Assets, by Transfer or Transferee [Axis] Qualitative and Quantitative Information, Transferor's Continuing Involvement in Transferred Financial Assets, Transfer or Transferee [Domain] Qualitative and Quantitative Information, Transferor's Continuing Involvement in Transferred Financial Assets, Transfer or Transferee [Domain] Underlying Asset Class [Axis] Underlying Asset Class [Axis] Underlying Asset Class [Domain] Underlying Asset Class [Domain] Single Class MBS, REMIC & Megas [Member] Single Class MBS, REMIC & Megas [Member] Fannie Mae Single-class Mortgage-Backed Securities (MBS) are MBS in which the investors receive principal and interest payments in proportion to their percentage ownership of the MBS issuance. Fannie Mae Megas are large pools of Fannie Mae MBS backed by smaller pools of Fannie Mae MBS or by other Fannie Mae-backed Megas. Real Estate Mortgage Investment Conduit (REMIC) refers to a type of mortgage-related security in which interest and principal payments from mortgages or mortgage-related securities are structured into separately traded securities. Stripped Mortgage-Backed Securities (SMBS) are created by "stripping" or separating the principal and interest payments from the underlying pool of mortgages into two classes of securities, with each receiving a different proportion of the principal and interest payments. Transfers of Financial Assets [Line Items] Assumption for Fair Value as of Balance Sheet Date of Assets or Liabilities that relate to Transferor's Continuing Involvement [Line Items] Portfolio securitizations: unpaid principal balance Unpaid Principal Balance of Portfolio Securitizations We are considered to be the transferor when we transfer assets from our portfolio in a portfolio securitization transaction and the following represents the unpaid principal balance of portfolio securitizations which occurred during the period. Retained interests: unpaid principal balance Unpaid Principal Balance Securities Retained Unconsolidated Portfolio Securitization Trusts Represents the unpaid principal balance of securities retained in unconsolidated portfolio securitization trusts as of the period end. Retained interest: fair value Fair Value Securities Retained Unconsolidated Portfolio Securitization Trusts Represents the fair value of securities retained in unconsolidated portfolio securitization trusts as of the period end. Retained interests: principal and interest received Cash Flows Between Transferor and Transferee, Beneficial Interest Offsetting Offsetting [Table Text Block] Tabular disclosure of derivative, other financial assets and liabilities that are subject to offsetting, including master netting arrangements. Investments in Securities Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Estimated mark-to-market loan-to-value ratio less than or equal to 80% [Member] Estimated Mark To Market Loan To Value Ratio Less Than or Equal to 80 Percent [Member] Represents the recorded investment in loans with an estimated mark-to-market loan-to-value ratio less than or equal to 80%. Estimated mark-to-market loan-to-value ratio greater than 80% and less than or equal to 90% [Member] Estimated Mark To Market Loan To Value Ratio Greater Than 80 Percent and Less Than or Equal to 90 Percent [Member] Represents the recorded investment in loans with an estimated mark-to-market loan-to-value ratio greater than 80% and less than or equal to 90%. Estimated mark-to-market loan-to-value ratio greater than 90% and less than or equal to 100% [Member] Estimated Mark To Market Loan To Value Ratio Greater Than 90 Percent and Less Than or Equal to 100 Percent [Member] Represents the recorded investment in loans with an estimated mark-to-market loan-to-value ratio greater than 90% and less than or equal to 100%. Estimated mark-to-market loan-to-value ratio greater than 100% [Member] Estimated Mark To Market Loan To Value Ratio Greater Than 100 Percent, Loans Recorded Investment [Member] Estimated Mark To Market Loan To Value Ratio Greater Than 100 Percent, Loans Recorded Investment [Member] Allowance for Loan Losses Roll Forward by Segment Financing Receivable, Allowance for Credit Loss [Table Text Block] Allowance for Loan Losses and Total Recorded Investment in HFI Loans Number of loans troubled debt restructurings subsequent default Financing Receivable, Troubled Debt Restructuring, Subsequent Default, Number of Contracts Recorded investment troubled debt restructurings subsequent default Financing Receivable, Troubled Debt Restructuring, Subsequent Default Fair Value Measurements Using Significant Unobservable Inputs (Level3) [Table] Fair Value Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation Table [Table] Summarization of information required and determined to be provided for purposes of reconciling beginning and ending balances of fair value measurements of assets and liabilities using significant unobservable inputs (Level 3). Such reconciliation, separately presenting changes during the period, at a minimum, may include: (1) total gains or losses for the period (realized and unrealized), segregating those gains or losses included in earnings (or changes in net assets or liabilities), and a description of where those gains or losses included in earnings (or changes in net assets or liabilities) are reported in the statement of income (or activities); (2) purchases, sales, issuances, and settlements (net); and (3) transfers in and transfers out of Level 3 (for example, transfers due to changes in the observability of significant inputs). Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Other Comprehensive Income (Loss) [Member] Other Comprehensive Income (Loss) [Member] Trading Assets, Excluding Debt and Equity Securities [Member] Net derivatives [Member] Derivative [Member] Net Unrealized Gains (Losses) included in net income related to assets still held Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss) Net unrealized Gains (Losses) included in net income related to liabilities still held Fair Value, Liability, Recurring Basis, Still Held, Unrealized Gain (Loss) Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Beginning Balance Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value Total gains or (losses) (realized/unrealized) Included in Net Income Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings Total gains or (losses) (realized/unrealized) Included in Other Comprehensive Income (Loss) Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss) Purchases Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases Sales Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales Issues Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances Settlements Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements Transfers out of Level 3 Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 Transfers into Level 3 Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 Ending Balance Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Beginning Balance Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value Total gains (losses) (realized/unrealized) Included in Net Income Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings Total gains (losses) Included in Other Comprehensive Income Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Other Comprehensive Income (Loss) Purchases Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Purchases Sales Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Sales Issues Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Issuances Settlements Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements Transfers out of Level 3 Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3 Transfers Into Level 3 Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers Into Level 3 Ending Balance Allowance for Loan Losses Allowance for Credit Losses [Text Block] Concentrations of Credit Risk Concentration Risk Disclosure [Text Block] Segment Reporting Segment Reporting Disclosure [Text Block] Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Senior Preferred Stock Senior Preferred Stock [Member] Senior Preferred Stock is senior in liquidation preference to Fannie Mae common stock and all other series of preferred stock. Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] Two-year Constant Maturity U.S. Treasury Rate [Member] Two-year Maturity U.S. Treasury Rate [Member] An index based on the average yield of a range of Treasury securities, adjusted to the equivalent of a two-year maturity. Ten-year Constant Maturity U.S. Treasury Rate [Member] Ten-year Maturity U.S. Treasury Rate [Member] An index based on the average yield of a range of Treasury securities, adjusted to the equivalent of a 10-year maturity. Three-Month LIBOR [Member] Three-Month LIBOR [Member] An index based on the interest rate at which banks in the London wholesale money markets will lend to each other for a three month loan. Series D Preferred Stock [Member] Series D Preferred Stock [Member] Series E Preferred Stock [Member] Series E Preferred Stock [Member] Series F Preferred Stock [Member] Series F Preferred Stock [Member] Series G Preferred Stock [Member] Series G Preferred Stock [Member] Series H Preferred Stock [Member] Series H Preferred Stock [Member] Series I Preferred Stock [Member] Series I Preferred Stock [Member] Outstanding Series I Preferred Stock. This stock has no par value, is non-participating, is non-voting and has a liquidation preference equal to the stated value per share. Series L Preferred Stock [Member] Series L Preferred Stock [Member] Outstanding Series L Preferred Stock. This stock has no par value, is non-participating, is non-voting and has a liquidation preference equal to the stated value per share. Series M Preferred Stock [Member] Series M Preferred Stock [Member] Outstanding Series M Preferred Stock. This stock has no par value, is non-participating, is non-voting and has a liquidation preference equal to the stated value per share. Series N Preferred Stock [Member] Series N Preferred Stock [Member] Outstanding Series N Preferred Stock. This stock has no par value, is non-participating, is non-voting and has a liquidation preference equal to the stated value per share. Series O Preferred Stock [Member] Series O Preferred Stock [Member] Outstanding Series O Preferred Stock. This stock has no par value, is non-participating, is non-voting and has a redemption price of $50 to $52.50 depending on the year of redemption. Convertible Series 2004-1 Preferred Stock [Member] Convertible Series 2004-1 Preferred Stock [Member] Outstanding Convertible Series 2004-1 Preferred Stock, convertible at any time, at the option of holders, into shares of Fannie Mae common stock. The conversion price is adjustable, as necessary, to maintain the stated conversion rate into common stock. Series P Preferred Stock [Member] Series P Preferred Stock [Member] Outstanding Series P Preferred Stock classified within stockholders' equity has no par value, is non-participating, is non-voting and has a liquidation preference equal to the stated value per share. Series Q Preferred Stock [Member] Series Q Preferred Stock [Member] Outstanding Series Q Preferred Stock. This stock has no par value, is non-participating, is non-voting and has a liquidation preference equal to the stated value per share. Series R Preferred Stock [Member] Series R Preferred Stock [Member] Outstanding Series R Preferred Stock. This stock has no par value, is non-participating, is non-voting and has a liquidation preference equal to the stated value per share. Series S Preferred Stock [Member] Series S Preferred Stock [Member] 7.75% fixed to floating rate non-cumulative Preferred Series S Stock. Series T Preferred Stock [Member] Series T Preferred Stock [Member] Outstanding Series T Preferred Stock. This stock has no par value, is non-participating, is non-voting and has a liquidation preference equal to the stated value per share. Class of Stock [Line Items] Class of Stock [Line Items] Shares, Outstanding Shares, Outstanding Senior preferred stock value Senior preferred stock issued, shares Senior preferred stock, shares outstanding Senior preferred stock, stated value per share Senior Preferred Stock, Par or Stated Value Per Share Senior Preferred Stock, Par or Stated Value Per Share Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Preferred stock, shares issued Preferred Stock, Value, Issued Preferred stock, shares outstanding Common Stock, Shares, Outstanding Preferred stock outstanding, amount Preferred Stock, Value, Outstanding Preferred stock, stated value per share Preferred Stock, Par or Stated Value Per Share Preferred stock, annual dividend rate (as a percent) Preferred Stock, Dividend Rate, Percentage Capital reserve amount for the fiscal year based on the amended Senior Preferred Stock Purchase agreement Reduction in Dividends Paid Reduction in Dividends Paid Represents the amount of dividends are reduced. Annual Reduction of Capital Reserve Amount from 2013 to 2017, Senior Preferred Stock Purchase Agreement, Amendment Annual Reduction of Capital Reserve Amount from 2013 to 2018, Senior Preferred Stock Purchase Agreement, Amendment Represents the amount of annual reduction to the capital reserve for the fiscal years 2013-2018 per the amended senior preferred stock purchase agreement between the company and U.S.Treasury. Preferred Stock, Redemption Terms Preferred Stock, Redemption Terms Preferred stock dividend rate, basis spread on variable rate Preferred Stock, Dividend Rate, Basis Spread on Variable Rate The percentage points added to the reference rate to compute the variable dividend rate on the annual dividend rate. Convertible Stock, Conversion Price Convertible Stock, Conversion Price The price per share of the conversion of the convertible series 2004-1 preferred stock to Fannie Mae common stock. Conversion Stock, Conversion Rate Conversion Stock, Conversion Rate Rate of conversion to common stock associated with each share of series 2004-1 preferred stock. Preferred Stock, Redemption Price Per Share Preferred Stock, Redemption Price Per Share Estimated mark-to-market LTV ratio greater than 100% [Member] Estimated Mark to Market Loan to Value Ratio Greater Than One Hundred Percent [Member] Represents the percentage of loans with an estimated mark-to-market loan-to-value ratio greater than 100%. 2004 and Prior Vintages 2004 and Prior [Member] Loan origination year 2004 and prior. 2005 - 2008 Vintages 2005 to 2008 [Member] Loan origination year 2005 to 2008. 2009 - 2019 Vintages 2009 to Current Year [Member] Loan origination year 2009 to current year. California CALIFORNIA Florida FLORIDA ILLINOIS ILLINOIS New Jersey NEW JERSEY New York NEW YORK All other states Other States [Member] Represents all other states not presented separately in the table. 60 days delinquent (percentage of book of business) Loans 60 to 89 Days Past Due, Percentage of Unpaid Principal Balance Represents the percentage of unpaid principal balance comprised of loans 60 to 89 days past due. Calculated based on the aggregate unpaid principal balance for the category indicated, divided by the respective book of business. 30 days delinquent (percentage of conventional loans) Number of Loans 30 to 59 Days Past Due, Percentage Represents the percentage of loans that are 30 to 59 days past due. Calculated based on the number of loans in the delinquency bucket indicated, divided by the total number of loans in the respective category. 60 days delinquent (percentage of conventional loans) Number of Loans 60 to 89 Days Past Due, Percentage Represents the percentage of loans that are 60 to 89 days past due. Calculated based on the number of loans in the delinquency bucket indicated, divided by the total number of loans in the respective category. Seriously delinquent (percentage of conventional loans) Number of Loans Seriously Delinquent, Percentage by Category Represents the percentage of single-family loans greater than or equal to 90 days past due or multifamily loans greater than or equal to 60 days past due, included in each category. Calculated based on the number of loans in the delinquency bucket indicated, divided by the total number of loans in the respective category. Number of Reportable Segments Number of Reportable Segments Preferred Stock Preferred Stock [Member] Common Stock Accumulated Deficit Retained Earnings [Member] Accumulated Other Comprehensive Income Treasury Stock Treasury Stock [Member] Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Balance (shares) Balance Senior preferred stock dividends paid per share Comprehensive income: Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest [Abstract] Net income Net Income (Loss) Attributable to Parent Other comprehensive income, net of tax effect: Other Comprehensive Income (Loss), Net of Tax [Abstract] Changes in net unrealized gains on available-for-sale securities (net of taxes of $28, $21 and $0, respectively) Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax Reclassification adjustment for gains included in net income (net of taxes of $139, $70 and $48, respectively) Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax Prior service cost and actuarial gains, net of amortization for defined benefit plans (net of tax) Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax Other, (net of taxes of $0, $0 and $3, respectively) Other Comprehensive Income, Other, Net of Tax Other Stockholders' Equity, Other Total comprehensive income Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Reclassification related to Tax Cuts and Jobs Act Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings, Tax Effect Balance Balance (shares) Fair Value Option Fair Value Measurement, Policy [Policy Text Block] Equity Stockholders' Equity Note Disclosure [Text Block] Financing Receivable, Past Due [Table] Financing Receivable, Past Due [Table] Financial Asset, Period Past Due [Axis] Financial Asset, Period Past Due [Axis] Financial Asset, Period Past Due [Domain] Financial Asset, Period Past Due [Domain] 30 to 59 Days Past Due [Member] Financial Asset, 30 to 59 Days Past Due [Member] 60 to 89 Days Past Due [Member] Financial Asset, 60 to 89 Days Past Due [Member] Seriously Delinquent [Member] Financial Asset, Equal to or Greater than 90 Days Past Due [Member] Financing Receivable, Past Due [Line Items] Financing Receivable, Past Due [Line Items] Days delinquent, recorded investment Financing Receivable, Past Due Current, recorded investment Financing Receivable, Not Past Due Recorded investment in loans 90 days or more delinquent and accruing interest Financing Receivable, 90 Days or More Past Due, Still Accruing Recorded investment in nonaccrual loans Financing Receivable, Nonaccrual Total amortized cost Debt Securities, Available-for-sale, Amortized Cost Gross unrealized gains Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax Gross unrealized losses Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax Total fair value Available-for-sale Securities, Debt Maturities, Single Maturity Date, Rolling Maturity Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost, Rolling Maturity [Abstract] One Year or Less, Amortized Cost Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Amortized Cost One Year or Less, Fair Value Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Fair Value After One Year through Five Years, Amortized Cost Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Amortized Cost After One Year through Five Years, Fair Value Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Fair Value After Five Years through Ten Years, Amortized Cost Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after Five Through Ten Years, Amortized Cost After Five Years through Ten Years, Fair Value Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after Five Through Ten Years, Fair Value After Ten Years, Amortized Cost Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Amortized Cost After Ten Years, Fair Value Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value Weighted average yield Available-for-sale Debt Securities, Weighted Average Yield Represent weighted average yield of available-for-sale debt securities at cost, net of adjustments, maturing in the next fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments. Yield are determined by dividing interest income by amortized cost balances as of year-end. One Year or Less, weighted average yield Available-for-sale Securities, Debt Maturities, Next Twelve Months, Weighted Average Yield Represent weighted average yield of available-for-sale debt securities at cost, net of adjustments, maturing in the next fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments. Yield are determined by dividing interest income by amortized cost balances as of year-end. After One Year through Five Years, weighted average yield Available-for-sale Securities, Debt Maturities, Year Two Through Five, Weighted Average Yield Represent the weighted average yield of available-for-sale debt securities at cost, net of adjustments, maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments. Yields are determined by dividing income by amortized cost balances as of year-end. After Five Years through Ten Years, weighted average yield Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Weighted Average Yield Represent the weighted average yield of available-for-sale debt securities at cost, net of adjustments, maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments. Yields are determined by dividing interest income by amortized cost balances as of year-end. After Ten Years, weighted average yield Available-for-sale Securities, Debt Maturities, after Ten Years, Weighted Average Yield Represent the weighted average yield of available-for-sale debt securities at cost, net of adjustments, maturing after the tenth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.Available-for-sale Securities, Debt Maturities, after Ten Years. Yields are determined by dividing interest income by amortized cost balances as of year-end. Geographic Concentration Risk [Member] Geographic Concentration Risk [Member] Schedule of Risk in Force Mortgage Insurance Coverage Schedule of Risk in Force Mortgage Insurance Coverage [Table Text Block] Tabular disclosure of risk in force mortgage insurance coverage. Schedules of Concentration of Risk, by Risk Factor Schedules of Concentration of Risk, by Risk Factor [Table Text Block] Schedule of Delinquency Status Guaranty Book of Business Schedule of Delinquency Status Guaranty Book of Business [Table Text Block] Tabular disclosure of current delinquency status of our single-family conventional and total multifamily guaranty book of business. Schedule of Risk Characteristics Guaranty Book of Business Schedule of Risk Characteristics Guaranty Book of Business [Table Text Block] Tabular disclosure of certain higher risk characteristics of our single-family conventional and total multifamily guarantee book of business. Schedule of Risk in Force Mortgage Insurance Coverage, by Counterparty Schedule of Risk in Force Mortgage Insurance Coverage, by Counterparty [Table Text Block] Tabular disclosure of risk in force mortgage mortgage insurance coverage by counterparty. Income Tax Income Tax Disclosure [Text Block] Preferred Stock Schedule of Stock by Class [Table Text Block] Percentage Of Common Shares Attributable to Warrants Issued to Treasury as Percentage to Total Diluted Common Shares Senior Preferred Stock, Par or Stated Value Per Share Conversion price per share Conversion rate Shares of variable liquidation preference senior preferred stock issued Value assigned to Treasury's commitment and recorded as a reduction to additional paid-in-capital Adjustments to Additional Paid in Capital, Other Total remaining funding available from US Treasury pursuant to the senior preferred stock agreement Total Available Funding from Treasury Pursuant to the Senior Preferred Stock Agreement Represents total available funding from U.S. Treasury pursuant to the senior preferred stock agreement after 2012 if we do not have a positive net worth as of December 31, 2012. In the event we have a positive net worth as of December 31, 2012, then the amount of funding available after 2012 under the amended senior preferred stock purchase agreement will depend on the size of that positive net worth relative to the cumulative draws for net worth deficiencies attributable to periods during 2010, 2011, and 2012, as follows: 1) If our positive net worth as of December 31, 2012 is less than the cumulative draws for net worth deficiencies attributable to periods during 2010, 2011, and 2012, then the amount of available funding will be $124.8 billion less our positive net worth as of December 31, 2012. 2) If our positive net worth as of December 31, 2012 is greater than the cumulative draws for net worth deficiencies attributable to periods during 2010, 2011, and 2012, then the amount of available funding will be $124.8 billion less the cumulative draws attributable to periods during 2010, 2011, and 2012. Preferred Stock Covenant Maximum Fair Market Value of assets and properties per transaction Preferred Stock Covenant Maximum Fair Market Value of assets and properties per transaction Preferred Stock Covenant Maximum Fair Market Value of assets and properties per transaction or series of transactions in which Fannie Mae may sell without written consent of Treasury. Preferred Stock, Covenant, Current Period Debt v.s. Maximum Mortgage Assets Allowed at Prior Year End, Maximum Ratio Preferred Stock, Covenant, Current Period Debt v.s. Maximum Mortgage Assets Allowed at Prior Year End, Maximum Ratio The maximum ratio of debt as of the end of the current period to maximum mortgage assets allowed as of the end of the prior year end, per the related covenant in the Senior Preferred Stock Agreement. Preferred Stock, Covenant, Maximum Mortgage Assets Preferred Stock, Covenant, Maximum Mortgage Assets The maximum mortgage assets amount, as of the end of the current period, allowed per the covenant in the Senior Preferred Stock Agreement. Payment Of Cash Dividends On Senior Preferred Stock To Treasury Debt Instrument, Face Amount Mortgage Loans SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Text Block] Statement of Comprehensive Income [Abstract] Long-term debt interest expense Fair Value Option, Disclosures [Table] Fair Value Option, Disclosures [Table] Eligible Item or Group for Fair Value Option [Axis] Fair Value, Option, Eligible Item or Group [Domain] Loans [Member] Loans Receivable [Member] Long-term debt [Member] Loans, unpaid principal balance Principal Amount Outstanding Of Loans Held For Investment Represents principal amount outstanding of loans held for investment. Long-Term Debt, unpaid principal balance Fair value of nonaccrual loans Fair Value, Option, Loans Held as Assets, Aggregate Amount in Nonaccrual Status Difference between unpaid principal balance and the fair value of nonaccrual loans Fair Value, Option, Loans Held as Assets, Aggregate Amount in Nonaccrual Status, Aggregated Difference Fair value of loans that are 90 days past due Fair Value, Option, Loans Held as Assets, 90 Days or More Past Due Difference between unpaid principal balance and the fair value of these 90 days or more days past due loans Fair Value, Option, Loans Held as Assets, 90 Days or More Past Due, Aggregate Difference Fair Value, Option, Changes in Fair Value, Gain (Loss) Fair Value, Option, Changes in Fair Value, Gain (Loss) Mortgage loans Short-term debt Long-term debt Net interest income Non-interest Income: Noninterest Income [Abstract] Administrative expenses: General and Administrative Expense [Abstract] Foreclosed property expense Foreclosed Real Estate Expense Temporary Payroll Tax Cut Continuation Act of 2011 (“TCCA”) fees Total comprehensive income Changes in unrealized gains on available-for-sale securities, net of reclassification adjustments and taxes Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, after Tax Total comprehensive income attributable to Fannie Mae Net income attributable to Fannie Mae Dividends distributed or amounts attributable to senior preferred stock Earnings (loss) per share: Basic Weighted Average Number of Shares Outstanding, Basic Mortgage commitments to purchase whole loans Mortgage Commitments to Purchase Whole Loans [Member] Represent forward contract/commitments to purchase single-family mortgage whole loans. Forward contracts to purchase mortgage-related securities Forward Contracts to Purchase Mortgage-related Securities [Member] Represents forward contract/commitment to purchase mortgage-related securities. Forward contracts to sell mortgage-related securities Forward Contracts to Sell Mortgage-related Securities [Member] Represents forward contract/commitment to sell mortgage-related securities. Asset Derivatives [Abstract] Derivative Asset [Abstract] Notional amount Derivative Asset, Notional Amount Derivative asset, estimated fair value Derivative, Fair Value, Gross Asset, All Derivatives Fair value of derivative asset, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position. Includes all derivative assets subject to and not subject to master netting arrangements. Accrued interest receivable Derivative Assets Interest Receivable Represents carrying amount of interest earned on derivative assets but not received, as of the balance sheet date. Total net risk management derivatives - Asset Derivative Liabilities [Abstract] Derivative Liability [Abstract] Notional amount Derivative Liability, Notional Amount Derivative liability, estimated fair value Derivative Liability, Fair Value, Gross Liability, All Derivatives Fair value of derivative liability, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position. Includes all derivatives liability subject and not subject to master netting arrangements. Accrued interest payable Derivative Liability, Interest Payable Represents carrying value of accrued interest payable on derivative liabilities that has been incurred and is unpaid, as of the balance sheet date. Netting adjustment Total net risk management derivatives - Liability Cash collateral posted for derivative instruments Derivative Asset, Collateral, Obligation to Return Cash, Offset Cash collateral received for derivative instruments Derivative Liability, Collateral, Right to Reclaim Cash, Offset Segments [Axis] Federal Housing Finance Agency [Member] Federal Housing Finance Agency [Member] Conservator to Government sponsored agencies. Common Securitization Solutions [Member] Common Securitization Solutions [Member] Jointly owned limited liability company formed to design, develop, build and ultimately operate a common securitization platform. Other Expense [Member] Other Expense [Member] Aggregate Liquidation Preference of Senior Preferred Stock Home Affordable Modification Program Administrative Expense Reimbursement Home Affordable Modification Program Administrative Expense Reimbursement Represents administrative expense reimbursement received from U.S. Treasury and Freddie Mac for expenses relating to U.S. Treasury's Home Affordable Modification Program. Increase of Guarantee Fee Rate Resulting from the Temporary Payroll Tax Cut Continuation Act of 2011. Increase of Guarantee Fee Rate Resulting from the Temporary Payroll Tax Cut Continuation Act of 2011. Increase in guaranty fee on single-family residential mortgages required by the Temporary Payroll Tax Cut Continuation Act of 2011. Recognized TCCA fees that had not been remitted to Treasury as of period end Liability to Treasury Related to Increase in Single-Family Guaranty Fee Resulting from the Temporary Payroll Tax Cut Continuation Act of 2011 A liability due to the Treasury related to the increased guaranty fee result from the Temporary Payroll Tax Cut Continuation Act of 2011. Basis Points of Each Dollar of Unpaid Principal Balance Basis Points of Each Dollar of Unpaid Principal Balance Represents the number of basis points for each dollar of the unpaid principal balance of its total new business purchases that Fannie Mae must set aside to fund the Housing Trust Fund and Capital Magnet Fund as required by the Federal Housing Finance Regulatory Reform Act of 2008, which was enacted on July 30, 2008. Affordable Housing Program Obligation Affordable Housing Program Obligation Affordable Housing Program Assessments Affordable Housing Program Assessments FHFA assessment fees/expense FHFA assessment fees/expense Fees paid to FHFA semi-annually as required by HERA Act for operating expenses and maintaining working capital. Payments to Acquire Equity Method Investments Payments to Acquire Equity Method Investments Cumulative Effect of New Accounting Principle in Period of Adoption Allowance Rollforward [Table] Financing Receivable, Allowance for Credit Loss [Table] Allowance for Loan Losses [Line Items] Financing Receivable, Allowance for Credit Loss [Line Items] Allowance for Loan Losses [Roll Forward] Allowance for Loan and Lease Losses [Roll Forward] Beginning balance Benefit (provision) for loan losses Financing Receivable, Credit Loss, Expense (Reversal) Charge-offs Allowance for Loan and Lease Losses, Write-offs Recoveries Allowance for Loan and Lease Loss, Recovery of Bad Debts Other Allowance for Loan and Lease Losses, Adjustments, Other Ending balance