XML 40 R81.htm IDEA: XBRL DOCUMENT v2.4.1.9
Investments in Securities Other-than-temporary Impairments 4 (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2014
Subprime private-label securities [Member]  
UPB and Modeled Attributes [Line Items]  
Unpaid principal balance $ 7,164us-gaap_InvestmentOwnedBalancePrincipalAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_MortgageBackedSecuritiesIssuedByPrivateEnterprisesSubprimeMember
Weighted average collateral default (percent) 47.70%fnm_WeightedAverageCollateralDefault
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_MortgageBackedSecuritiesIssuedByPrivateEnterprisesSubprimeMember
Weighted average collateral severities (percent) 64.80%fnm_WeightedAverageCollateralSeverities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_MortgageBackedSecuritiesIssuedByPrivateEnterprisesSubprimeMember
Weighted average voluntary prepayment rates (percent) 2.40%fnm_WeightedAverageVoluntaryPrepaymentRates
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_MortgageBackedSecuritiesIssuedByPrivateEnterprisesSubprimeMember
Average credit enhancement (percent) 15.70%fnm_AverageCreditEnhancement
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_MortgageBackedSecuritiesIssuedByPrivateEnterprisesSubprimeMember
Alt-A Option ARM [Member]  
UPB and Modeled Attributes [Line Items]  
Unpaid principal balance 1,132us-gaap_InvestmentOwnedBalancePrincipalAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAAdjustableRateMortgageMember
Weighted average collateral default (percent) 34.80%fnm_WeightedAverageCollateralDefault
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAAdjustableRateMortgageMember
Weighted average collateral severities (percent) 49.70%fnm_WeightedAverageCollateralSeverities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAAdjustableRateMortgageMember
Weighted average voluntary prepayment rates (percent) 7.00%fnm_WeightedAverageVoluntaryPrepaymentRates
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAAdjustableRateMortgageMember
Average credit enhancement (percent) 4.10%fnm_AverageCreditEnhancement
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAAdjustableRateMortgageMember
Alt-A Fixed Rate [Member]  
UPB and Modeled Attributes [Line Items]  
Unpaid principal balance 1,939us-gaap_InvestmentOwnedBalancePrincipalAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAFixedRateMember
Weighted average collateral default (percent) 15.70%fnm_WeightedAverageCollateralDefault
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAFixedRateMember
Weighted average collateral severities (percent) 49.50%fnm_WeightedAverageCollateralSeverities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAFixedRateMember
Weighted average voluntary prepayment rates (percent) 11.40%fnm_WeightedAverageVoluntaryPrepaymentRates
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAFixedRateMember
Average credit enhancement (percent) 4.90%fnm_AverageCreditEnhancement
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAFixedRateMember
Alt-A Variable Rate [Member]  
UPB and Modeled Attributes [Line Items]  
Unpaid principal balance 1,271us-gaap_InvestmentOwnedBalancePrincipalAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAVariableRateMember
Weighted average collateral default (percent) 25.90%fnm_WeightedAverageCollateralDefault
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAVariableRateMember
Weighted average collateral severities (percent) 44.50%fnm_WeightedAverageCollateralSeverities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAVariableRateMember
Weighted average voluntary prepayment rates (percent) 7.80%fnm_WeightedAverageVoluntaryPrepaymentRates
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAVariableRateMember
Average credit enhancement (percent) 5.80%fnm_AverageCreditEnhancement
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAVariableRateMember
Alt-A Hybrid Rate [Member]  
UPB and Modeled Attributes [Line Items]  
Unpaid principal balance 2,350us-gaap_InvestmentOwnedBalancePrincipalAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAHybridRateMember
Weighted average collateral default (percent) 16.30%fnm_WeightedAverageCollateralDefault
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAHybridRateMember
Weighted average collateral severities (percent) 40.40%fnm_WeightedAverageCollateralSeverities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAHybridRateMember
Weighted average voluntary prepayment rates (percent) 10.60%fnm_WeightedAverageVoluntaryPrepaymentRates
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAHybridRateMember
Average credit enhancement (percent) 3.40%fnm_AverageCreditEnhancement
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAHybridRateMember
2004 and Prior [Member] | Subprime private-label securities [Member]  
UPB and Modeled Attributes [Line Items]  
Unpaid principal balance 110us-gaap_InvestmentOwnedBalancePrincipalAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_MortgageBackedSecuritiesIssuedByPrivateEnterprisesSubprimeMember
/ fnm_VintagesAxis
= fnm_Year2004AndPriorSecuritiesMember
Weighted average collateral default (percent) 26.40%fnm_WeightedAverageCollateralDefault
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_MortgageBackedSecuritiesIssuedByPrivateEnterprisesSubprimeMember
/ fnm_VintagesAxis
= fnm_Year2004AndPriorSecuritiesMember
Weighted average collateral severities (percent) 56.30%fnm_WeightedAverageCollateralSeverities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_MortgageBackedSecuritiesIssuedByPrivateEnterprisesSubprimeMember
/ fnm_VintagesAxis
= fnm_Year2004AndPriorSecuritiesMember
Weighted average voluntary prepayment rates (percent) 8.20%fnm_WeightedAverageVoluntaryPrepaymentRates
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_MortgageBackedSecuritiesIssuedByPrivateEnterprisesSubprimeMember
/ fnm_VintagesAxis
= fnm_Year2004AndPriorSecuritiesMember
Average credit enhancement (percent) 39.20%fnm_AverageCreditEnhancement
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_MortgageBackedSecuritiesIssuedByPrivateEnterprisesSubprimeMember
/ fnm_VintagesAxis
= fnm_Year2004AndPriorSecuritiesMember
2004 and Prior [Member] | Alt-A Option ARM [Member]  
UPB and Modeled Attributes [Line Items]  
Unpaid principal balance 110us-gaap_InvestmentOwnedBalancePrincipalAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAAdjustableRateMortgageMember
/ fnm_VintagesAxis
= fnm_Year2004AndPriorSecuritiesMember
Weighted average collateral default (percent) 26.40%fnm_WeightedAverageCollateralDefault
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAAdjustableRateMortgageMember
/ fnm_VintagesAxis
= fnm_Year2004AndPriorSecuritiesMember
Weighted average collateral severities (percent) 54.60%fnm_WeightedAverageCollateralSeverities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAAdjustableRateMortgageMember
/ fnm_VintagesAxis
= fnm_Year2004AndPriorSecuritiesMember
Weighted average voluntary prepayment rates (percent) 9.20%fnm_WeightedAverageVoluntaryPrepaymentRates
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAAdjustableRateMortgageMember
/ fnm_VintagesAxis
= fnm_Year2004AndPriorSecuritiesMember
Average credit enhancement (percent) 3.90%fnm_AverageCreditEnhancement
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAAdjustableRateMortgageMember
/ fnm_VintagesAxis
= fnm_Year2004AndPriorSecuritiesMember
2004 and Prior [Member] | Alt-A Fixed Rate [Member]  
UPB and Modeled Attributes [Line Items]  
Unpaid principal balance 794us-gaap_InvestmentOwnedBalancePrincipalAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAFixedRateMember
/ fnm_VintagesAxis
= fnm_Year2004AndPriorSecuritiesMember
Weighted average collateral default (percent) 8.30%fnm_WeightedAverageCollateralDefault
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAFixedRateMember
/ fnm_VintagesAxis
= fnm_Year2004AndPriorSecuritiesMember
Weighted average collateral severities (percent) 45.90%fnm_WeightedAverageCollateralSeverities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAFixedRateMember
/ fnm_VintagesAxis
= fnm_Year2004AndPriorSecuritiesMember
Weighted average voluntary prepayment rates (percent) 14.00%fnm_WeightedAverageVoluntaryPrepaymentRates
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAFixedRateMember
/ fnm_VintagesAxis
= fnm_Year2004AndPriorSecuritiesMember
Average credit enhancement (percent) 11.30%fnm_AverageCreditEnhancement
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAFixedRateMember
/ fnm_VintagesAxis
= fnm_Year2004AndPriorSecuritiesMember
2004 and Prior [Member] | Alt-A Variable Rate [Member]  
UPB and Modeled Attributes [Line Items]  
Unpaid principal balance 121us-gaap_InvestmentOwnedBalancePrincipalAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAVariableRateMember
/ fnm_VintagesAxis
= fnm_Year2004AndPriorSecuritiesMember
Weighted average collateral default (percent) 17.20%fnm_WeightedAverageCollateralDefault
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAVariableRateMember
/ fnm_VintagesAxis
= fnm_Year2004AndPriorSecuritiesMember
Weighted average collateral severities (percent) 37.80%fnm_WeightedAverageCollateralSeverities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAVariableRateMember
/ fnm_VintagesAxis
= fnm_Year2004AndPriorSecuritiesMember
Weighted average voluntary prepayment rates (percent) 9.40%fnm_WeightedAverageVoluntaryPrepaymentRates
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAVariableRateMember
/ fnm_VintagesAxis
= fnm_Year2004AndPriorSecuritiesMember
Average credit enhancement (percent) 23.30%fnm_AverageCreditEnhancement
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAVariableRateMember
/ fnm_VintagesAxis
= fnm_Year2004AndPriorSecuritiesMember
2004 and Prior [Member] | Alt-A Hybrid Rate [Member]  
UPB and Modeled Attributes [Line Items]  
Unpaid principal balance 305us-gaap_InvestmentOwnedBalancePrincipalAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAHybridRateMember
/ fnm_VintagesAxis
= fnm_Year2004AndPriorSecuritiesMember
Weighted average collateral default (percent) 11.70%fnm_WeightedAverageCollateralDefault
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAHybridRateMember
/ fnm_VintagesAxis
= fnm_Year2004AndPriorSecuritiesMember
Weighted average collateral severities (percent) 36.40%fnm_WeightedAverageCollateralSeverities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAHybridRateMember
/ fnm_VintagesAxis
= fnm_Year2004AndPriorSecuritiesMember
Weighted average voluntary prepayment rates (percent) 10.70%fnm_WeightedAverageVoluntaryPrepaymentRates
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAHybridRateMember
/ fnm_VintagesAxis
= fnm_Year2004AndPriorSecuritiesMember
Average credit enhancement (percent) 9.90%fnm_AverageCreditEnhancement
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAHybridRateMember
/ fnm_VintagesAxis
= fnm_Year2004AndPriorSecuritiesMember
2005 [Member] | Subprime private-label securities [Member]  
UPB and Modeled Attributes [Line Items]  
Unpaid principal balance 8us-gaap_InvestmentOwnedBalancePrincipalAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_MortgageBackedSecuritiesIssuedByPrivateEnterprisesSubprimeMember
/ fnm_VintagesAxis
= fnm_Year2005SecuritiesMember
Weighted average collateral default (percent) 47.00%fnm_WeightedAverageCollateralDefault
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_MortgageBackedSecuritiesIssuedByPrivateEnterprisesSubprimeMember
/ fnm_VintagesAxis
= fnm_Year2005SecuritiesMember
Weighted average collateral severities (percent) 69.70%fnm_WeightedAverageCollateralSeverities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_MortgageBackedSecuritiesIssuedByPrivateEnterprisesSubprimeMember
/ fnm_VintagesAxis
= fnm_Year2005SecuritiesMember
Weighted average voluntary prepayment rates (percent) 3.90%fnm_WeightedAverageVoluntaryPrepaymentRates
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_MortgageBackedSecuritiesIssuedByPrivateEnterprisesSubprimeMember
/ fnm_VintagesAxis
= fnm_Year2005SecuritiesMember
Average credit enhancement (percent) 60.30%fnm_AverageCreditEnhancement
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_MortgageBackedSecuritiesIssuedByPrivateEnterprisesSubprimeMember
/ fnm_VintagesAxis
= fnm_Year2005SecuritiesMember
2005 [Member] | Alt-A Option ARM [Member]  
UPB and Modeled Attributes [Line Items]  
Unpaid principal balance 451us-gaap_InvestmentOwnedBalancePrincipalAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAAdjustableRateMortgageMember
/ fnm_VintagesAxis
= fnm_Year2005SecuritiesMember
Weighted average collateral default (percent) 31.50%fnm_WeightedAverageCollateralDefault
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAAdjustableRateMortgageMember
/ fnm_VintagesAxis
= fnm_Year2005SecuritiesMember
Weighted average collateral severities (percent) 53.60%fnm_WeightedAverageCollateralSeverities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAAdjustableRateMortgageMember
/ fnm_VintagesAxis
= fnm_Year2005SecuritiesMember
Weighted average voluntary prepayment rates (percent) 7.40%fnm_WeightedAverageVoluntaryPrepaymentRates
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAAdjustableRateMortgageMember
/ fnm_VintagesAxis
= fnm_Year2005SecuritiesMember
Average credit enhancement (percent) 7.50%fnm_AverageCreditEnhancement
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAAdjustableRateMortgageMember
/ fnm_VintagesAxis
= fnm_Year2005SecuritiesMember
2005 [Member] | Alt-A Fixed Rate [Member]  
UPB and Modeled Attributes [Line Items]  
Unpaid principal balance 771us-gaap_InvestmentOwnedBalancePrincipalAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAFixedRateMember
/ fnm_VintagesAxis
= fnm_Year2005SecuritiesMember
Weighted average collateral default (percent) 19.90%fnm_WeightedAverageCollateralDefault
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAFixedRateMember
/ fnm_VintagesAxis
= fnm_Year2005SecuritiesMember
Weighted average collateral severities (percent) 49.00%fnm_WeightedAverageCollateralSeverities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAFixedRateMember
/ fnm_VintagesAxis
= fnm_Year2005SecuritiesMember
Weighted average voluntary prepayment rates (percent) 10.10%fnm_WeightedAverageVoluntaryPrepaymentRates
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAFixedRateMember
/ fnm_VintagesAxis
= fnm_Year2005SecuritiesMember
Average credit enhancement (percent) 0.60%fnm_AverageCreditEnhancement
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAFixedRateMember
/ fnm_VintagesAxis
= fnm_Year2005SecuritiesMember
2005 [Member] | Alt-A Variable Rate [Member]  
UPB and Modeled Attributes [Line Items]  
Unpaid principal balance 277us-gaap_InvestmentOwnedBalancePrincipalAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAVariableRateMember
/ fnm_VintagesAxis
= fnm_Year2005SecuritiesMember
Weighted average collateral default (percent) 27.10%fnm_WeightedAverageCollateralDefault
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAVariableRateMember
/ fnm_VintagesAxis
= fnm_Year2005SecuritiesMember
Weighted average collateral severities (percent) 47.20%fnm_WeightedAverageCollateralSeverities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAVariableRateMember
/ fnm_VintagesAxis
= fnm_Year2005SecuritiesMember
Weighted average voluntary prepayment rates (percent) 8.30%fnm_WeightedAverageVoluntaryPrepaymentRates
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAVariableRateMember
/ fnm_VintagesAxis
= fnm_Year2005SecuritiesMember
Average credit enhancement (percent) 13.20%fnm_AverageCreditEnhancement
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAVariableRateMember
/ fnm_VintagesAxis
= fnm_Year2005SecuritiesMember
2005 [Member] | Alt-A Hybrid Rate [Member]  
UPB and Modeled Attributes [Line Items]  
Unpaid principal balance 1,096us-gaap_InvestmentOwnedBalancePrincipalAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAHybridRateMember
/ fnm_VintagesAxis
= fnm_Year2005SecuritiesMember
Weighted average collateral default (percent) 20.70%fnm_WeightedAverageCollateralDefault
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAHybridRateMember
/ fnm_VintagesAxis
= fnm_Year2005SecuritiesMember
Weighted average collateral severities (percent) 41.20%fnm_WeightedAverageCollateralSeverities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAHybridRateMember
/ fnm_VintagesAxis
= fnm_Year2005SecuritiesMember
Weighted average voluntary prepayment rates (percent) 9.20%fnm_WeightedAverageVoluntaryPrepaymentRates
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAHybridRateMember
/ fnm_VintagesAxis
= fnm_Year2005SecuritiesMember
Average credit enhancement (percent) 3.10%fnm_AverageCreditEnhancement
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAHybridRateMember
/ fnm_VintagesAxis
= fnm_Year2005SecuritiesMember
2006 [Member] | Subprime private-label securities [Member]  
UPB and Modeled Attributes [Line Items]  
Unpaid principal balance 6,718us-gaap_InvestmentOwnedBalancePrincipalAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_MortgageBackedSecuritiesIssuedByPrivateEnterprisesSubprimeMember
/ fnm_VintagesAxis
= fnm_Year2006SecuritiesMember
Weighted average collateral default (percent) 48.10%fnm_WeightedAverageCollateralDefault
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_MortgageBackedSecuritiesIssuedByPrivateEnterprisesSubprimeMember
/ fnm_VintagesAxis
= fnm_Year2006SecuritiesMember
Weighted average collateral severities (percent) 66.70%fnm_WeightedAverageCollateralSeverities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_MortgageBackedSecuritiesIssuedByPrivateEnterprisesSubprimeMember
/ fnm_VintagesAxis
= fnm_Year2006SecuritiesMember
Weighted average voluntary prepayment rates (percent) 2.30%fnm_WeightedAverageVoluntaryPrepaymentRates
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_MortgageBackedSecuritiesIssuedByPrivateEnterprisesSubprimeMember
/ fnm_VintagesAxis
= fnm_Year2006SecuritiesMember
Average credit enhancement (percent) 15.00%fnm_AverageCreditEnhancement
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_MortgageBackedSecuritiesIssuedByPrivateEnterprisesSubprimeMember
/ fnm_VintagesAxis
= fnm_Year2006SecuritiesMember
2006 [Member] | Alt-A Option ARM [Member]  
UPB and Modeled Attributes [Line Items]  
Unpaid principal balance 571us-gaap_InvestmentOwnedBalancePrincipalAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAAdjustableRateMortgageMember
/ fnm_VintagesAxis
= fnm_Year2006SecuritiesMember
Weighted average collateral default (percent) 39.10%fnm_WeightedAverageCollateralDefault
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAAdjustableRateMortgageMember
/ fnm_VintagesAxis
= fnm_Year2006SecuritiesMember
Weighted average collateral severities (percent) 46.60%fnm_WeightedAverageCollateralSeverities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAAdjustableRateMortgageMember
/ fnm_VintagesAxis
= fnm_Year2006SecuritiesMember
Weighted average voluntary prepayment rates (percent) 6.30%fnm_WeightedAverageVoluntaryPrepaymentRates
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAAdjustableRateMortgageMember
/ fnm_VintagesAxis
= fnm_Year2006SecuritiesMember
Average credit enhancement (percent) 1.50%fnm_AverageCreditEnhancement
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAAdjustableRateMortgageMember
/ fnm_VintagesAxis
= fnm_Year2006SecuritiesMember
2006 [Member] | Alt-A Fixed Rate [Member]  
UPB and Modeled Attributes [Line Items]  
Unpaid principal balance 374us-gaap_InvestmentOwnedBalancePrincipalAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAFixedRateMember
/ fnm_VintagesAxis
= fnm_Year2006SecuritiesMember
Weighted average collateral default (percent) 22.50%fnm_WeightedAverageCollateralDefault
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAFixedRateMember
/ fnm_VintagesAxis
= fnm_Year2006SecuritiesMember
Weighted average collateral severities (percent) 53.10%fnm_WeightedAverageCollateralSeverities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAFixedRateMember
/ fnm_VintagesAxis
= fnm_Year2006SecuritiesMember
Weighted average voluntary prepayment rates (percent) 8.40%fnm_WeightedAverageVoluntaryPrepaymentRates
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAFixedRateMember
/ fnm_VintagesAxis
= fnm_Year2006SecuritiesMember
Average credit enhancement (percent) 0.10%fnm_AverageCreditEnhancement
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAFixedRateMember
/ fnm_VintagesAxis
= fnm_Year2006SecuritiesMember
2006 [Member] | Alt-A Variable Rate [Member]  
UPB and Modeled Attributes [Line Items]  
Unpaid principal balance 873us-gaap_InvestmentOwnedBalancePrincipalAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAVariableRateMember
/ fnm_VintagesAxis
= fnm_Year2006SecuritiesMember
Weighted average collateral default (percent) 26.80%fnm_WeightedAverageCollateralDefault
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAVariableRateMember
/ fnm_VintagesAxis
= fnm_Year2006SecuritiesMember
Weighted average collateral severities (percent) 44.20%fnm_WeightedAverageCollateralSeverities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAVariableRateMember
/ fnm_VintagesAxis
= fnm_Year2006SecuritiesMember
Weighted average voluntary prepayment rates (percent) 7.40%fnm_WeightedAverageVoluntaryPrepaymentRates
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAVariableRateMember
/ fnm_VintagesAxis
= fnm_Year2006SecuritiesMember
Average credit enhancement (percent) 1.10%fnm_AverageCreditEnhancement
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAVariableRateMember
/ fnm_VintagesAxis
= fnm_Year2006SecuritiesMember
2006 [Member] | Alt-A Hybrid Rate [Member]  
UPB and Modeled Attributes [Line Items]  
Unpaid principal balance 872us-gaap_InvestmentOwnedBalancePrincipalAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAHybridRateMember
/ fnm_VintagesAxis
= fnm_Year2006SecuritiesMember
Weighted average collateral default (percent) 11.90%fnm_WeightedAverageCollateralDefault
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAHybridRateMember
/ fnm_VintagesAxis
= fnm_Year2006SecuritiesMember
Weighted average collateral severities (percent) 40.70%fnm_WeightedAverageCollateralSeverities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAHybridRateMember
/ fnm_VintagesAxis
= fnm_Year2006SecuritiesMember
Weighted average voluntary prepayment rates (percent) 12.50%fnm_WeightedAverageVoluntaryPrepaymentRates
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAHybridRateMember
/ fnm_VintagesAxis
= fnm_Year2006SecuritiesMember
Average credit enhancement (percent) 0.00%fnm_AverageCreditEnhancement
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAHybridRateMember
/ fnm_VintagesAxis
= fnm_Year2006SecuritiesMember
2007 and After [Member] | Subprime private-label securities [Member]  
UPB and Modeled Attributes [Line Items]  
Unpaid principal balance 328us-gaap_InvestmentOwnedBalancePrincipalAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_MortgageBackedSecuritiesIssuedByPrivateEnterprisesSubprimeMember
/ fnm_VintagesAxis
= fnm_Year2007AndAfterSecuritiesMember
Weighted average collateral default (percent) 46.10%fnm_WeightedAverageCollateralDefault
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_MortgageBackedSecuritiesIssuedByPrivateEnterprisesSubprimeMember
/ fnm_VintagesAxis
= fnm_Year2007AndAfterSecuritiesMember
Weighted average collateral severities (percent) 25.50%fnm_WeightedAverageCollateralSeverities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_MortgageBackedSecuritiesIssuedByPrivateEnterprisesSubprimeMember
/ fnm_VintagesAxis
= fnm_Year2007AndAfterSecuritiesMember
Weighted average voluntary prepayment rates (percent) 1.30%fnm_WeightedAverageVoluntaryPrepaymentRates
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_MortgageBackedSecuritiesIssuedByPrivateEnterprisesSubprimeMember
/ fnm_VintagesAxis
= fnm_Year2007AndAfterSecuritiesMember
Average credit enhancement (percent) 20.60%fnm_AverageCreditEnhancement
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_MortgageBackedSecuritiesIssuedByPrivateEnterprisesSubprimeMember
/ fnm_VintagesAxis
= fnm_Year2007AndAfterSecuritiesMember
2007 and After [Member] | Alt-A Option ARM [Member]  
UPB and Modeled Attributes [Line Items]  
Unpaid principal balance 0us-gaap_InvestmentOwnedBalancePrincipalAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAAdjustableRateMortgageMember
/ fnm_VintagesAxis
= fnm_Year2007AndAfterSecuritiesMember
2007 and After [Member] | Alt-A Fixed Rate [Member]  
UPB and Modeled Attributes [Line Items]  
Unpaid principal balance 0us-gaap_InvestmentOwnedBalancePrincipalAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAFixedRateMember
/ fnm_VintagesAxis
= fnm_Year2007AndAfterSecuritiesMember
2007 and After [Member] | Alt-A Variable Rate [Member]  
UPB and Modeled Attributes [Line Items]  
Unpaid principal balance 0us-gaap_InvestmentOwnedBalancePrincipalAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAVariableRateMember
/ fnm_VintagesAxis
= fnm_Year2007AndAfterSecuritiesMember
2007 and After [Member] | Alt-A Hybrid Rate [Member]  
UPB and Modeled Attributes [Line Items]  
Unpaid principal balance $ 77us-gaap_InvestmentOwnedBalancePrincipalAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAHybridRateMember
/ fnm_VintagesAxis
= fnm_Year2007AndAfterSecuritiesMember
Weighted average collateral default (percent) 20.70%fnm_WeightedAverageCollateralDefault
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAHybridRateMember
/ fnm_VintagesAxis
= fnm_Year2007AndAfterSecuritiesMember
Weighted average collateral severities (percent) 36.20%fnm_WeightedAverageCollateralSeverities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAHybridRateMember
/ fnm_VintagesAxis
= fnm_Year2007AndAfterSecuritiesMember
Weighted average voluntary prepayment rates (percent) 9.80%fnm_WeightedAverageVoluntaryPrepaymentRates
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAHybridRateMember
/ fnm_VintagesAxis
= fnm_Year2007AndAfterSecuritiesMember
Average credit enhancement (percent) 20.50%fnm_AverageCreditEnhancement
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= fnm_AltAHybridRateMember
/ fnm_VintagesAxis
= fnm_Year2007AndAfterSecuritiesMember