XML 149 R126.htm IDEA: XBRL DOCUMENT v2.4.1.9
Fair Value Financial Instruments (Details) (USD $)
Dec. 31, 2014
Dec. 31, 2013
Carrying Value [Member]    
Financial assets [Abstract]    
Cash and cash equivalents and restricted cash $ 54,565,000,000fnm_CashCashEquivalentsAndRestrictedCashFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
$ 48,223,000,000fnm_CashCashEquivalentsAndRestrictedCashFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
Federal funds sold and securities purchased under agreements to resell or similar arrangements 30,950,000,000us-gaap_FederalFundsSoldAndSecuritiesBorrowedOrPurchasedUnderAgreementsToResellFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
38,975,000,000us-gaap_FederalFundsSoldAndSecuritiesBorrowedOrPurchasedUnderAgreementsToResellFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
Trading securities 31,504,000,000us-gaap_TradingSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
30,768,000,000us-gaap_TradingSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
Available-for-sale securities 30,654,000,000us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
38,171,000,000us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
Mortgage loans held for sale 331,000,000us-gaap_MortgagesHeldForSaleFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
380,000,000us-gaap_MortgagesHeldForSaleFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
Mortgage loans held for investment 3,019,163,000,000us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
3,025,860,000,000us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
Advances to lenders 5,559,000,000fnm_AdvancesToLendersFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
3,727,000,000fnm_AdvancesToLendersFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
Derivatives assets at fair value 1,485,000,000us-gaap_DerivativeAssets
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
2,073,000,000us-gaap_DerivativeAssets
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
Guaranty assets and buy-ups 210,000,000fnm_GuarantyAssetsAndBuyUpsFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
267,000,000fnm_GuarantyAssetsAndBuyUpsFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
Total Financial assets 3,174,421,000,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
3,188,444,000,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
Financial liabilities [Abstract]    
Federal Funds Purchased and Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure 50,000,000us-gaap_FederalFundsPurchasedAndSecuritiesLoanedOrSoldUnderAgreementsToRepurchaseFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
 
Derivative liabilities at fair value 614,000,000us-gaap_DerivativeLiabilities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
1,469,000,000us-gaap_DerivativeLiabilities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
Guaranty obligations 382,000,000us-gaap_GuaranteesFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
485,000,000us-gaap_GuaranteesFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
Total Financial liabilities 3,223,201,000,000us-gaap_LiabilitiesFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
3,236,477,000,000us-gaap_LiabilitiesFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
Netting Adjustment [Member]    
Financial assets [Abstract]    
Cash and cash equivalents and restricted cash 0fnm_CashCashEquivalentsAndRestrictedCashFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
0fnm_CashCashEquivalentsAndRestrictedCashFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
Federal funds sold and securities purchased under agreements to resell or similar arrangements 0us-gaap_FederalFundsSoldAndSecuritiesBorrowedOrPurchasedUnderAgreementsToResellFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
0us-gaap_FederalFundsSoldAndSecuritiesBorrowedOrPurchasedUnderAgreementsToResellFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
Trading securities 0us-gaap_TradingSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
0us-gaap_TradingSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
Available-for-sale securities 0us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
0us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
Mortgage loans held for sale 0us-gaap_MortgagesHeldForSaleFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
0us-gaap_MortgagesHeldForSaleFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
Mortgage loans held for investment 0us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
0us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
Advances to lenders 0fnm_AdvancesToLendersFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
0fnm_AdvancesToLendersFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
Derivatives assets at fair value (5,186,000,000)us-gaap_DerivativeAssets
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
(8,422,000,000)us-gaap_DerivativeAssets
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
Guaranty assets and buy-ups 0fnm_GuarantyAssetsAndBuyUpsFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
0fnm_GuarantyAssetsAndBuyUpsFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
Total Financial assets (5,186,000,000)us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
(8,422,000,000)us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
Financial liabilities [Abstract]    
Federal Funds Purchased and Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure 0us-gaap_FederalFundsPurchasedAndSecuritiesLoanedOrSoldUnderAgreementsToRepurchaseFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
 
Derivative liabilities at fair value (10,194,000,000)us-gaap_DerivativeLiabilities
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
(9,370,000,000)us-gaap_DerivativeLiabilities
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
Guaranty obligations 0us-gaap_GuaranteesFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
0us-gaap_GuaranteesFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
Total Financial liabilities (10,194,000,000)us-gaap_LiabilitiesFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
(9,370,000,000)us-gaap_LiabilitiesFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
Estimated Fair Value [Member]    
Financial assets [Abstract]    
Cash and cash equivalents and restricted cash 54,565,000,000fnm_CashCashEquivalentsAndRestrictedCashFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
48,223,000,000fnm_CashCashEquivalentsAndRestrictedCashFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
Federal funds sold and securities purchased under agreements to resell or similar arrangements 30,950,000,000us-gaap_FederalFundsSoldAndSecuritiesBorrowedOrPurchasedUnderAgreementsToResellFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
38,975,000,000us-gaap_FederalFundsSoldAndSecuritiesBorrowedOrPurchasedUnderAgreementsToResellFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
Trading securities 31,504,000,000us-gaap_TradingSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
30,768,000,000us-gaap_TradingSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
Available-for-sale securities 30,654,000,000us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
38,171,000,000us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
Mortgage loans held for sale 338,000,000us-gaap_MortgagesHeldForSaleFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
380,000,000us-gaap_MortgagesHeldForSaleFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
Mortgage loans held for investment 3,088,086,000,000us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
2,992,022,000,000us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
Advances to lenders 5,549,000,000fnm_AdvancesToLendersFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
3,688,000,000fnm_AdvancesToLendersFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
Derivatives assets at fair value 1,485,000,000us-gaap_DerivativeAssets
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
2,073,000,000us-gaap_DerivativeAssets
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
Guaranty assets and buy-ups 616,000,000fnm_GuarantyAssetsAndBuyUpsFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
706,000,000fnm_GuarantyAssetsAndBuyUpsFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
Total Financial assets 3,243,747,000,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
3,155,006,000,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
Financial liabilities [Abstract]    
Federal Funds Purchased and Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure 50,000,000us-gaap_FederalFundsPurchasedAndSecuritiesLoanedOrSoldUnderAgreementsToRepurchaseFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
 
Derivative liabilities at fair value 614,000,000us-gaap_DerivativeLiabilities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
1,469,000,000us-gaap_DerivativeLiabilities
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
Guaranty obligations 1,579,000,000us-gaap_GuaranteesFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
2,433,000,000us-gaap_GuaranteesFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
Total Financial liabilities 3,312,687,000,000us-gaap_LiabilitiesFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
3,241,494,000,000us-gaap_LiabilitiesFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]    
Financial assets [Abstract]    
Cash and cash equivalents and restricted cash 37,965,000,000fnm_CashCashEquivalentsAndRestrictedCashFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
36,633,000,000fnm_CashCashEquivalentsAndRestrictedCashFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Federal funds sold and securities purchased under agreements to resell or similar arrangements 0us-gaap_FederalFundsSoldAndSecuritiesBorrowedOrPurchasedUnderAgreementsToResellFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
0us-gaap_FederalFundsSoldAndSecuritiesBorrowedOrPurchasedUnderAgreementsToResellFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Trading securities 19,466,000,000us-gaap_TradingSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
16,306,000,000us-gaap_TradingSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Available-for-sale securities 0us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
0us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Mortgage loans held for sale 0us-gaap_MortgagesHeldForSaleFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
0us-gaap_MortgagesHeldForSaleFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Mortgage loans held for investment 0us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
0us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Advances to lenders 0fnm_AdvancesToLendersFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
0fnm_AdvancesToLendersFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Derivatives assets at fair value 0us-gaap_DerivativeAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
0us-gaap_DerivativeAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Guaranty assets and buy-ups 0fnm_GuarantyAssetsAndBuyUpsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
0fnm_GuarantyAssetsAndBuyUpsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Total Financial assets 57,431,000,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
52,939,000,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Financial liabilities [Abstract]    
Federal Funds Purchased and Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure 0us-gaap_FederalFundsPurchasedAndSecuritiesLoanedOrSoldUnderAgreementsToRepurchaseFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
 
Derivative liabilities at fair value 0us-gaap_DerivativeLiabilities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
0us-gaap_DerivativeLiabilities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Guaranty obligations 0us-gaap_GuaranteesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
0us-gaap_GuaranteesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Total Financial liabilities 0us-gaap_LiabilitiesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
0us-gaap_LiabilitiesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Significant Other Observable Inputs (Level 2) [Member]    
Financial assets [Abstract]    
Cash and cash equivalents and restricted cash 16,600,000,000fnm_CashCashEquivalentsAndRestrictedCashFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
11,590,000,000fnm_CashCashEquivalentsAndRestrictedCashFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Federal funds sold and securities purchased under agreements to resell or similar arrangements 30,950,000,000us-gaap_FederalFundsSoldAndSecuritiesBorrowedOrPurchasedUnderAgreementsToResellFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
38,975,000,000us-gaap_FederalFundsSoldAndSecuritiesBorrowedOrPurchasedUnderAgreementsToResellFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Trading securities 9,008,000,000us-gaap_TradingSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
11,688,000,000us-gaap_TradingSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Available-for-sale securities 15,574,000,000us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
19,159,000,000us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Mortgage loans held for sale 169,000,000us-gaap_MortgagesHeldForSaleFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
185,000,000us-gaap_MortgagesHeldForSaleFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Mortgage loans held for investment 2,687,759,000,000us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
2,599,667,000,000us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Advances to lenders 5,079,000,000fnm_AdvancesToLendersFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
3,165,000,000fnm_AdvancesToLendersFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Derivatives assets at fair value 6,489,000,000us-gaap_DerivativeAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
10,430,000,000us-gaap_DerivativeAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Guaranty assets and buy-ups 0fnm_GuarantyAssetsAndBuyUpsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
0fnm_GuarantyAssetsAndBuyUpsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Total Financial assets 2,771,628,000,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
2,694,859,000,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Financial liabilities [Abstract]    
Federal Funds Purchased and Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure 50,000,000us-gaap_FederalFundsPurchasedAndSecuritiesLoanedOrSoldUnderAgreementsToRepurchaseFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
 
Derivative liabilities at fair value 10,671,000,000us-gaap_DerivativeLiabilities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
10,734,000,000us-gaap_DerivativeLiabilities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Guaranty obligations 0us-gaap_GuaranteesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
0us-gaap_GuaranteesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Total Financial liabilities 3,299,289,000,000us-gaap_LiabilitiesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
3,231,253,000,000us-gaap_LiabilitiesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Significant Unobservable Inputs (Level 3) [Member]    
Financial assets [Abstract]    
Cash and cash equivalents and restricted cash 0fnm_CashCashEquivalentsAndRestrictedCashFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
0fnm_CashCashEquivalentsAndRestrictedCashFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Federal funds sold and securities purchased under agreements to resell or similar arrangements 0us-gaap_FederalFundsSoldAndSecuritiesBorrowedOrPurchasedUnderAgreementsToResellFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
0us-gaap_FederalFundsSoldAndSecuritiesBorrowedOrPurchasedUnderAgreementsToResellFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Trading securities 3,030,000,000us-gaap_TradingSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
2,774,000,000us-gaap_TradingSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Available-for-sale securities 15,080,000,000us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
19,012,000,000us-gaap_AvailableForSaleSecurities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Mortgage loans held for sale 169,000,000us-gaap_MortgagesHeldForSaleFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
195,000,000us-gaap_MortgagesHeldForSaleFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Mortgage loans held for investment 400,327,000,000us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
392,355,000,000us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Advances to lenders 470,000,000fnm_AdvancesToLendersFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
523,000,000fnm_AdvancesToLendersFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Derivatives assets at fair value 182,000,000us-gaap_DerivativeAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
65,000,000us-gaap_DerivativeAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Guaranty assets and buy-ups 616,000,000fnm_GuarantyAssetsAndBuyUpsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
706,000,000fnm_GuarantyAssetsAndBuyUpsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Total Financial assets 419,874,000,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
415,630,000,000us-gaap_AssetsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Financial liabilities [Abstract]    
Federal Funds Purchased and Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure 0us-gaap_FederalFundsPurchasedAndSecuritiesLoanedOrSoldUnderAgreementsToRepurchaseFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
 
Derivative liabilities at fair value 137,000,000us-gaap_DerivativeLiabilities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
105,000,000us-gaap_DerivativeLiabilities
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Guaranty obligations 1,579,000,000us-gaap_GuaranteesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
2,433,000,000us-gaap_GuaranteesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Total Financial liabilities 23,592,000,000us-gaap_LiabilitiesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
19,611,000,000us-gaap_LiabilitiesFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Fannie Mae [Member]    
Financial liabilities [Abstract]    
Long-term debt 6,403,000,000us-gaap_LongTermDebtFairValue
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
1,308,000,000us-gaap_LongTermDebtFairValue
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
Fannie Mae [Member] | Carrying Value [Member]    
Financial assets [Abstract]    
Mortgage loans held for investment 239,243,000,000us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
259,638,000,000us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
Financial liabilities [Abstract]    
Short-term debt 105,012,000,000us-gaap_ShorttermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
72,295,000,000us-gaap_ShorttermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
Long-term debt 355,431,000,000us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
457,139,000,000us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
Fannie Mae [Member] | Netting Adjustment [Member]    
Financial assets [Abstract]    
Mortgage loans held for investment 0us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
0us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
Financial liabilities [Abstract]    
Short-term debt 0us-gaap_ShorttermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
0us-gaap_ShorttermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
Long-term debt 0us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
0us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
Fannie Mae [Member] | Estimated Fair Value [Member]    
Financial assets [Abstract]    
Mortgage loans held for investment 246,960,000,000us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
245,880,000,000us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
Financial liabilities [Abstract]    
Short-term debt 105,022,000,000us-gaap_ShorttermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
72,304,000,000us-gaap_ShorttermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
Long-term debt 368,685,000,000us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
465,548,000,000us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
Fannie Mae [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]    
Financial assets [Abstract]    
Mortgage loans held for investment 0us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
0us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
Financial liabilities [Abstract]    
Short-term debt 0us-gaap_ShorttermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
0us-gaap_ShorttermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
Long-term debt 0us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
0us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
Fannie Mae [Member] | Significant Other Observable Inputs (Level 2) [Member]    
Financial assets [Abstract]    
Mortgage loans held for investment 29,896,000,000us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
29,920,000,000us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
Financial liabilities [Abstract]    
Short-term debt 105,022,000,000us-gaap_ShorttermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
72,304,000,000us-gaap_ShorttermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
Long-term debt 367,703,000,000us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
463,991,000,000us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
Fannie Mae [Member] | Significant Unobservable Inputs (Level 3) [Member]    
Financial assets [Abstract]    
Mortgage loans held for investment 217,064,000,000us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
215,960,000,000us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
Financial liabilities [Abstract]    
Short-term debt 0us-gaap_ShorttermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
0us-gaap_ShorttermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
Long-term debt 982,000,000us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
1,557,000,000us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
Consolidated Trusts [Member]    
Financial assets [Abstract]    
Mortgage loans held for investment 15,629,000,000us-gaap_LoansReceivableFairValueDisclosure
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
14,268,000,000us-gaap_LoansReceivableFairValueDisclosure
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Financial liabilities [Abstract]    
Long-term debt 19,483,000,000us-gaap_LongTermDebtFairValue
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
14,976,000,000us-gaap_LongTermDebtFairValue
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Consolidated Trusts [Member] | Carrying Value [Member]    
Financial assets [Abstract]    
Mortgage loans held for investment 2,779,920,000,000us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
2,766,222,000,000us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Financial liabilities [Abstract]    
Short-term debt 1,560,000,000us-gaap_ShorttermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
2,154,000,000us-gaap_ShorttermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Long-term debt 2,760,152,000,000us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
2,702,935,000,000us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Consolidated Trusts [Member] | Netting Adjustment [Member]    
Financial assets [Abstract]    
Mortgage loans held for investment 0us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
0us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Financial liabilities [Abstract]    
Short-term debt 0us-gaap_ShorttermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
0us-gaap_ShorttermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Long-term debt 0us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
0us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= fnm_NettingAdjustmentMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Consolidated Trusts [Member] | Estimated Fair Value [Member]    
Financial assets [Abstract]    
Mortgage loans held for investment 2,841,126,000,000us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
2,746,142,000,000us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Financial liabilities [Abstract]    
Short-term debt 1,560,000,000us-gaap_ShorttermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
2,154,000,000us-gaap_ShorttermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Long-term debt 2,835,177,000,000us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
2,697,586,000,000us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Consolidated Trusts [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]    
Financial assets [Abstract]    
Mortgage loans held for investment 0us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
0us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Financial liabilities [Abstract]    
Short-term debt 0us-gaap_ShorttermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
0us-gaap_ShorttermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Long-term debt 0us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
0us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Consolidated Trusts [Member] | Significant Other Observable Inputs (Level 2) [Member]    
Financial assets [Abstract]    
Mortgage loans held for investment 2,657,863,000,000us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
2,569,747,000,000us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Financial liabilities [Abstract]    
Short-term debt 0us-gaap_ShorttermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
0us-gaap_ShorttermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Long-term debt 2,815,843,000,000us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
2,684,224,000,000us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Consolidated Trusts [Member] | Significant Unobservable Inputs (Level 3) [Member]    
Financial assets [Abstract]    
Mortgage loans held for investment 183,263,000,000us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
176,395,000,000us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Financial liabilities [Abstract]    
Short-term debt 1,560,000,000us-gaap_ShorttermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
2,154,000,000us-gaap_ShorttermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Long-term debt 19,334,000,000us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
13,362,000,000us-gaap_LongTermDebtFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
HARP Loans [Member]    
Financial liabilities [Abstract]    
Loans Receivable Refinanced under Home Affordable Refinance Program, Fair Value Disclosure 314,000,000,000fnm_LoansReceivableRefinancedUnderHomeAffordableRefinanceProgramFairValueDisclosure
/ fnm_NewAccountPronouncementEffectOfChangeOnAssetsByTypeAxis
= fnm_HomeAffordableRefinanceProgramHarpLoansMember
306,900,000,000fnm_LoansReceivableRefinancedUnderHomeAffordableRefinanceProgramFairValueDisclosure
/ fnm_NewAccountPronouncementEffectOfChangeOnAssetsByTypeAxis
= fnm_HomeAffordableRefinanceProgramHarpLoansMember
HARP Loans [Member] | Fair Value Estimation Process [Member]    
Financial Instruments [Line Items]    
Change In Estimated Fair Value Resulting From Change In Principal Market $ 3,300,000,000fnm_ChangeInEstimatedFairValueResultingFromChangeInPrincipalMarkets
/ us-gaap_ChangeInAccountingEstimateByTypeAxis
= fnm_FairValueEstimationProcessMember
/ fnm_NewAccountPronouncementEffectOfChangeOnAssetsByTypeAxis
= fnm_HomeAffordableRefinanceProgramHarpLoansMember
$ 11,500,000,000fnm_ChangeInEstimatedFairValueResultingFromChangeInPrincipalMarkets
/ us-gaap_ChangeInAccountingEstimateByTypeAxis
= fnm_FairValueEstimationProcessMember
/ fnm_NewAccountPronouncementEffectOfChangeOnAssetsByTypeAxis
= fnm_HomeAffordableRefinanceProgramHarpLoansMember