XML 108 R82.htm IDEA: XBRL DOCUMENT v2.4.1.9
Concentrations of Credit Risk Risk Characteristics - SF (Details) (Single-Family [Member])
3 Months Ended 12 Months Ended
Mar. 31, 2015
Dec. 31, 2014
Guaranty Book of Business [Member] | Conventional Loan [Member]
   
Accounts, Notes, Loans and Financing Receivable [Line Items]    
30 days delinquent, percentage (unpaid principal balance) 1.11%fnm_Loans30To59DaysPastDuePercentageOfUnpaidPrincipalBalance
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
1.27%fnm_Loans30To59DaysPastDuePercentageOfUnpaidPrincipalBalance
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
60 days delinquent, percentage (unpaid principal balance) 0.33%fnm_Loans60To89DaysPastDuePercentageOfUnpaidPrincipalBalance
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
0.38%fnm_Loans60To89DaysPastDuePercentageOfUnpaidPrincipalBalance
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
Seriously delinquent, percentage (unpaid principal balance) 1.87%fnm_LoansSeriouslyDelinquentPercentageOfUnpaidPrincipalBalance
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
1.99%fnm_LoansSeriouslyDelinquentPercentageOfUnpaidPrincipalBalance
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
30 days delinquent, percentage (loan count) 1.26%fnm_NumberOfLoans30To59DaysPastDuePercentage
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
1.47%fnm_NumberOfLoans30To59DaysPastDuePercentage
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
60 days delinquent, percentage (loan count) 0.36%fnm_NumberOfLoans60To89DaysPastDuePercentage
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
0.43%fnm_NumberOfLoans60To89DaysPastDuePercentage
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
Seriously delinquent, percentage (loan count) 1.78%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
1.89%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
Percentage of loans with detailed loan level information 99.00%fnm_PercentageOfLoansWithDetailedLoanLevelInformation
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
99.00%fnm_PercentageOfLoansWithDetailedLoanLevelInformation
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
Guaranty Book of Business [Member] | Conventional Loan [Member] | 2005 [Member]
   
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Percentage of book of business 3.00%fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ fnm_VintagesAxis
= fnm_Year2005Member
3.00%fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ fnm_VintagesAxis
= fnm_Year2005Member
Seriously delinquent, percentage (loan count) 5.94%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ fnm_VintagesAxis
= fnm_Year2005Member
6.18%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ fnm_VintagesAxis
= fnm_Year2005Member
Guaranty Book of Business [Member] | Conventional Loan [Member] | 2006 [Member]
   
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Percentage of book of business 3.00%fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ fnm_VintagesAxis
= fnm_Year2006Member
3.00%fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ fnm_VintagesAxis
= fnm_Year2006Member
Seriously delinquent, percentage (loan count) 9.14%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ fnm_VintagesAxis
= fnm_Year2006Member
9.61%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ fnm_VintagesAxis
= fnm_Year2006Member
Guaranty Book of Business [Member] | Conventional Loan [Member] | 2007 [Member]
   
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Percentage of book of business 4.00%fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ fnm_VintagesAxis
= fnm_Year2007Member
4.00%fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ fnm_VintagesAxis
= fnm_Year2007Member
Seriously delinquent, percentage (loan count) 10.34%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ fnm_VintagesAxis
= fnm_Year2007Member
10.79%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ fnm_VintagesAxis
= fnm_Year2007Member
Guaranty Book of Business [Member] | Conventional Loan [Member] | 2008 [Member]
   
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Percentage of book of business 2.00%fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ fnm_VintagesAxis
= fnm_Year2008Member
2.00%fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ fnm_VintagesAxis
= fnm_Year2008Member
Seriously delinquent, percentage (loan count) 6.05%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ fnm_VintagesAxis
= fnm_Year2008Member
6.27%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ fnm_VintagesAxis
= fnm_Year2008Member
Guaranty Book of Business [Member] | Conventional Loan [Member] | All other vintages [Member]
   
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Percentage of book of business 88.00%fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ fnm_VintagesAxis
= fnm_AllOtherVintagesMember
88.00%fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ fnm_VintagesAxis
= fnm_AllOtherVintagesMember
Seriously delinquent, percentage (loan count) 0.85%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ fnm_VintagesAxis
= fnm_AllOtherVintagesMember
0.88%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ fnm_VintagesAxis
= fnm_AllOtherVintagesMember
Guaranty Book of Business [Member] | Conventional Loan [Member] | Alt-A [Member]
   
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Percentage of book of business 4.00%fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ us-gaap_ProductOrServiceAxis
= fnm_AltAMortgageLoansMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
4.00%fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ us-gaap_ProductOrServiceAxis
= fnm_AltAMortgageLoansMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
Seriously delinquent, percentage (loan count) 7.41%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ us-gaap_ProductOrServiceAxis
= fnm_AltAMortgageLoansMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
7.77%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ us-gaap_ProductOrServiceAxis
= fnm_AltAMortgageLoansMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
Guaranty Book of Business [Member] | Conventional Loan [Member] | California
   
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Percentage of book of business 20.00%fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ us-gaap_StatementGeographicalAxis
= stpr_CA
20.00%fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ us-gaap_StatementGeographicalAxis
= stpr_CA
Seriously delinquent, percentage (loan count) 0.66%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ us-gaap_StatementGeographicalAxis
= stpr_CA
0.70%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ us-gaap_StatementGeographicalAxis
= stpr_CA
Guaranty Book of Business [Member] | Conventional Loan [Member] | Florida
   
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Percentage of book of business 6.00%fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ us-gaap_StatementGeographicalAxis
= stpr_FL
6.00%fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ us-gaap_StatementGeographicalAxis
= stpr_FL
Seriously delinquent, percentage (loan count) 3.91%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ us-gaap_StatementGeographicalAxis
= stpr_FL
4.42%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ us-gaap_StatementGeographicalAxis
= stpr_FL
Guaranty Book of Business [Member] | Conventional Loan [Member] | Illinois
   
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Percentage of book of business 4.00%fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ us-gaap_StatementGeographicalAxis
= stpr_IL
4.00%fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ us-gaap_StatementGeographicalAxis
= stpr_IL
Seriously delinquent, percentage (loan count) 2.20%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ us-gaap_StatementGeographicalAxis
= stpr_IL
2.36%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ us-gaap_StatementGeographicalAxis
= stpr_IL
Guaranty Book of Business [Member] | Conventional Loan [Member] | New Jersey
   
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Percentage of book of business 4.00%fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ us-gaap_StatementGeographicalAxis
= stpr_NJ
4.00%fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ us-gaap_StatementGeographicalAxis
= stpr_NJ
Seriously delinquent, percentage (loan count) 5.62%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ us-gaap_StatementGeographicalAxis
= stpr_NJ
5.78%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ us-gaap_StatementGeographicalAxis
= stpr_NJ
Guaranty Book of Business [Member] | Conventional Loan [Member] | New York
   
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Percentage of book of business 5.00%fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ us-gaap_StatementGeographicalAxis
= stpr_NY
5.00%fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ us-gaap_StatementGeographicalAxis
= stpr_NY
Seriously delinquent, percentage (loan count) 4.04%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ us-gaap_StatementGeographicalAxis
= stpr_NY
4.17%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ us-gaap_StatementGeographicalAxis
= stpr_NY
Guaranty Book of Business [Member] | Conventional Loan [Member] | All other states [Member]
   
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Percentage of book of business 61.00%fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ us-gaap_StatementGeographicalAxis
= fnm_OtherStatesMember
61.00%fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ us-gaap_StatementGeographicalAxis
= fnm_OtherStatesMember
Seriously delinquent, percentage (loan count) 1.43%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ us-gaap_StatementGeographicalAxis
= fnm_OtherStatesMember
1.52%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
/ us-gaap_StatementGeographicalAxis
= fnm_OtherStatesMember
Guaranty Book of Business [Member] | Conventional Loan [Member] | Estimated Mark to Market Loan to Value Ratio Greater Than 100% [Member]
   
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Percentage of book of business 5.00%fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
/ fnm_EstimatedMarkToMarketLoanToValueRatioAxis
= fnm_EstimatedMarkToMarketLoanToValueRatioGreaterThanOneHundredPercentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
5.00%fnm_PercentageOfUnpaidPrincipalBalanceOfLoans
/ fnm_EstimatedMarkToMarketLoanToValueRatioAxis
= fnm_EstimatedMarkToMarketLoanToValueRatioGreaterThanOneHundredPercentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
Seriously delinquent, percentage (loan count) 10.43%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ fnm_EstimatedMarkToMarketLoanToValueRatioAxis
= fnm_EstimatedMarkToMarketLoanToValueRatioGreaterThanOneHundredPercentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
10.98%fnm_NumberOfLoansSeriouslyDelinquentPercentageByCategory
/ fnm_EstimatedMarkToMarketLoanToValueRatioAxis
= fnm_EstimatedMarkToMarketLoanToValueRatioGreaterThanOneHundredPercentMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= fnm_ConventionalMortgageMember
/ fnm_RiskCharacteristicsOfOurBookOfBusinessAxis
= fnm_GuarantyBookOfBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= fnm_SingleFamilyMember
Minimum [Member]    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Serious delinquency, days past due 90 days 90 days