Mortgage Loans Individually Impaired Loans (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: unpaid principal balance	$ 194,372		$ 170,414
Individually impaired loans with related allowance recorded: total recorded investment	183,791	[1]	159,676	[1]
Individually impaired loans with related allowance recorded: related allowance for loan losses	48,610	[2]	46,857	[2]
Individually impaired loans with no related allowance recorded: unpaid principal balance	16,645	[3]	14,890	[3]
Individually impaired loans with no related allowance recorded: total recorded investment	12,908	[1],[3]	10,164	[1],[3]
Total individually impaired loans: unpaid principal balance	211,017	[2]	185,304	[2]
Total individually impaired loans: total recorded investment	196,699	[1],[2]	169,840	[1],[2]
Interest Receivable [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: related allowance for loan losses	1,062	[2]	1,081	[2]
Single-Family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: unpaid principal balance	192,049		167,582
Individually impaired loans with related allowance recorded: total recorded investment	181,449	[1]	156,821	[1]
Individually impaired loans with related allowance recorded: related allowance for loan losses	48,159		46,139
Individually impaired loans with no related allowance recorded: unpaid principal balance	15,025	[3]	13,131	[3]
Individually impaired loans with no related allowance recorded: total recorded investment	11,277	[1],[3]	8,393	[1],[3]
Table Footnote [Abstract]
Troubled debt restructuring recorded investment	190,100		161,900
Single-Family [Member] | Interest Receivable [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: related allowance for loan losses	1,049		1,049
Multifamily [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: unpaid principal balance	2,323		2,832
Individually impaired loans with related allowance recorded: total recorded investment	2,342	[1]	2,855	[1]
Individually impaired loans with related allowance recorded: related allowance for loan losses	451		718
Individually impaired loans with no related allowance recorded: unpaid principal balance	1,620	[3]	1,759	[3]
Individually impaired loans with no related allowance recorded: total recorded investment	1,631	[1],[3]	1,771	[1],[3]
Table Footnote [Abstract]
Troubled debt restructuring recorded investment	1,000		956
Multifamily [Member] | Interest Receivable [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: related allowance for loan losses	13		32
Primary [Member] | Single-Family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: unpaid principal balance	135,515	[4]	116,825	[4]
Individually impaired loans with related allowance recorded: total recorded investment	128,530	[1],[4]	109,684	[1],[4]
Individually impaired loans with related allowance recorded: related allowance for loan losses	31,132	[4]	29,598	[4]
Individually impaired loans with no related allowance recorded: unpaid principal balance	11,171	[3],[4]	9,370	[3],[4]
Individually impaired loans with no related allowance recorded: total recorded investment	8,875	[1],[3],[4]	6,471	[1],[3],[4]
Primary [Member] | Single-Family [Member] | Interest Receivable [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: related allowance for loan losses	668	[4]	674	[4]
Government [Member] | Single-Family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: unpaid principal balance	213	[5]	258	[5]
Individually impaired loans with related allowance recorded: total recorded investment	207	[1],[5]	258	[1],[5]
Individually impaired loans with related allowance recorded: related allowance for loan losses	39	[5]	67	[5]
Individually impaired loans with no related allowance recorded: unpaid principal balance	98	[3],[5]	25	[3],[5]
Individually impaired loans with no related allowance recorded: total recorded investment	98	[1],[3],[5]	17	[1],[3],[5]
Government [Member] | Single-Family [Member] | Interest Receivable [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: related allowance for loan losses	4	[5]	8	[5]
Alt-A [Member] | Single-Family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: unpaid principal balance	38,962		34,318
Individually impaired loans with related allowance recorded: total recorded investment	36,147	[1]	31,516	[1]
Individually impaired loans with related allowance recorded: related allowance for loan losses	11,707		11,121
Individually impaired loans with no related allowance recorded: unpaid principal balance	3,062	[3]	3,056	[3]
Individually impaired loans with no related allowance recorded: total recorded investment	1,858	[1],[3]	1,538	[1],[3]
Alt-A [Member] | Single-Family [Member] | Interest Receivable [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: related allowance for loan losses	285		268
Other [Member] | Single-Family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: unpaid principal balance	17,359	[6]	16,181	[6]
Individually impaired loans with related allowance recorded: total recorded investment	16,565	[1],[6]	15,363	[1],[6]
Individually impaired loans with related allowance recorded: related allowance for loan losses	5,281	[6]	5,353	[6]
Individually impaired loans with no related allowance recorded: unpaid principal balance	694	[3],[6]	680	[3],[6]
Individually impaired loans with no related allowance recorded: total recorded investment	446	[1],[3],[6]	367	[1],[3],[6]
Other [Member] | Single-Family [Member] | Interest Receivable [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: related allowance for loan losses	$ 92	[6]	$ 99	[6]

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

[2] Includes single-family loans restructured in a TDR with a recorded investment of $190.1 billion and $161.9 billion as of September 30, 2012 and December 31, 2011, respectively. Includes multifamily loans restructured in a TDR with a recorded investment of $1.0 billion and $956 million as of September 30, 2012 and December 31, 2011, respectively. 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.

[3] The discounted cash flows or collateral value equals or exceeds the carrying value of the loan and, as such, no valuation allowance is required.

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

[5] 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.

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