Mortgage Loans Aging (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 days delinquent	$ 52,745	[1]	$ 54,393	[1]
60 - 89 days delinquent	17,649	[1]	19,816	[1]
Seriously delinquent	103,802	[1],[2]	121,744	[1],[2]
Total delinquent	174,196	[1]	195,953	[1]
Current	2,834,778	[1]	2,782,938	[1]
Total	3,008,974	[1],[3]	2,978,891	[1]
Recorded investment in loans 90 days or more delinquent and accruing interest	544	[1]	548	[1]
Recorded investment in nonaccrual loans	122,155	[1]	142,612	[1]
Single-Family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 days delinquent	52,563	[1]	54,183	[1]
60 - 89 days delinquent	17,649	[1]	19,816	[1]
Seriously delinquent	103,340	[1],[2]	120,639	[1],[2]
Total delinquent	173,552	[1]	194,638	[1]
Current	2,648,553	[1]	2,605,032	[1]
Total	2,822,105	[1],[3]	2,799,670	[1]
Recorded investment in loans 90 days or more delinquent and accruing interest	544	[1]	548	[1]
Recorded investment in nonaccrual loans	120,275	[1]	139,848	[1]
Single-Family [Member] | Primary [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 days delinquent	42,795	[1],[4]	43,516	[1],[4]
60 - 89 days delinquent	13,814	[1],[4]	15,282	[1],[4]
Seriously delinquent	70,279	[1],[2],[4]	80,712	[1],[2],[4]
Total delinquent	126,888	[1],[4]	139,510	[1],[4]
Current	2,410,890	[1],[4]	2,341,646	[1],[4]
Total	2,537,778	[1],[4],[5],[6]	2,481,156	[1],[4],[5],[6]
Recorded investment in loans 90 days or more delinquent and accruing interest	109	[1],[4]	111	[1],[4]
Recorded investment in nonaccrual loans	83,933	[1],[4]	95,959	[1],[4]
Single-Family [Member] | Government [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 days delinquent	89	[1],[7]	109	[1],[7]
60 - 89 days delinquent	42	[1],[7]	49	[1],[7]
Seriously delinquent	334	[1],[2],[7]	327	[1],[2],[7]
Total delinquent	465	[1],[7]	485	[1],[7]
Current	50,614	[1],[7]	51,391	[1],[7]
Total	51,079	[1],[7]	51,876	[1],[7]
Recorded investment in loans 90 days or more delinquent and accruing interest	334	[1],[7]	327	[1],[7]
Recorded investment in nonaccrual loans	0	[1],[7]	0	[1],[7]
Single-Family [Member] | Alt-A [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 days delinquent	6,598	[1]	7,155	[1]
60 - 89 days delinquent	2,601	[1]	3,054	[1]
Seriously delinquent	23,588	[1],[2]	28,323	[1],[2]
Total delinquent	32,787	[1]	38,532	[1]
Current	125,493	[1]	138,880	[1]
Total	158,280	[1],[5],[6]	177,412	[1],[5],[6]
Recorded investment in loans 90 days or more delinquent and accruing interest	15	[1]	14	[1]
Recorded investment in nonaccrual loans	26,166	[1]	31,356	[1]
Single-Family [Member] | Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 days delinquent	3,081	[1],[8]	3,403	[1],[8]
60 - 89 days delinquent	1,192	[1],[8]	1,431	[1],[8]
Seriously delinquent	9,139	[1],[2],[8]	11,277	[1],[2],[8]
Total delinquent	13,412	[1],[8]	16,111	[1],[8]
Current	61,556	[1],[8]	73,115	[1],[8]
Total	74,968	[1],[5],[6],[8]	89,226	[1],[5],[6],[8]
Recorded investment in loans 90 days or more delinquent and accruing interest	86	[1],[8]	96	[1],[8]
Recorded investment in nonaccrual loans	10,176	[1],[8]	12,533	[1],[8]
Multifamily [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30 - 59 days delinquent	182	[1],[9]	210	[1],[9]
Seriously delinquent	462	[1],[2],[9]	1,105	[1],[2],[9]
Total delinquent	644	[1],[9]	1,315	[1],[9]
Current	186,225	[1],[9]	177,906	[1],[9]
Total	186,869	[1],[10],[3],[9]	179,221	[1],[10],[9]
Recorded investment in loans 90 days or more delinquent and accruing interest	0	[1],[9]	0	[1],[9]
Recorded investment in nonaccrual loans	$ 1,880	[1],[9]	$ 2,764	[1],[9]
Minimum [Member] | Single-Family [Member]
Table Footnote [Abstract]
Serious delinquency, days past due	90 days		90 days
Minimum [Member] | Multifamily [Member]
Table Footnote [Abstract]
Serious delinquency, days past due	60 days		60 days

[1] Recorded investment consists of unpaid principal balance, unamortized premiums, discounts and other cost basis adjustments, and accrued interest receivable.

[2] Single-family seriously delinquent loans are loans that are 90 days or more past due or in the foreclosure process. Multifamily seriously delinquent loans are loans that are 60 days or more past due.

[3] As of September 30, 2012, we began classifying as TDRs loans to certain borrowers who have received bankruptcy relief. These loans had a recorded investment of $22.9 billion and a related allowance of $1.1 billion as of September 30, 2012.

[4] Consists of mortgage loans that are not included in other loan classes.

[5] Excludes $51.1 billion and $51.9 billion as of September 30, 2012 and December 31, 2011, respectively, of mortgage loans guaranteed or insured, in whole or in part, by the U.S. government or one of its agencies that are not Alt-A loans. The segment class is primarily reverse mortgages for which we do not calculate an estimated mark-to-market LTV.

[6] The aggregate estimated mark-to-market LTV ratio is based on the unpaid principal balance of the loan as of the end of each reported period divided by the estimated current value of the property, which we calculate using an internal valuation model that estimates periodic changes in home value.

[7] Consists of mortgage loans guaranteed or insured, in whole or in part, by the U.S. government or one of its agencies that are not Alt-A. Primarily consists of reverse mortgages which due to their nature are not aged and are included in the current column.

[8] Includes loans with higher-risk loan characteristics, such as interest-only loans and negative-amortizing loans that are neither government nor Alt-A.

[9] Multifamily loans 60-89 days delinquent are included in the seriously delinquent column.

[10] Green (loan with acceptable risk); yellow (loan with signs of potential weakness); orange (loan with a well defined weakness that may jeopardize the timely full repayment); and red (loan with a weakness that makes timely collection or liquidation in full more questionable based on existing conditions and values).