Mortgage Loans Individually Impaired Loans (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: unpaid principal balance	$ 190,677		$ 170,414
Individually impaired loans with related allowance recorded: total recorded investment	180,519	[1]	159,676	[1]
Related allowance for loan losses	45,034	[2],[3]	46,857	[2],[3]
Individually impaired loans with no related allowance recorded: unpaid principal balance	23,594	[4]	14,890	[4]
Individually impaired loans with no related allowance recorded: total recorded investment	19,872	[1],[4]	10,164	[1],[4]
Total individually impaired loans: unpaid principal balance	214,271	[3]	185,304	[3]
Total individually impaired loans: total recorded investment	200,391	[1],[3]	169,840	[1],[3]
Interest Receivable [Member]
Financing Receivable, Impaired [Line Items]
Related allowance for loan losses	998	[3]	1,081	[3]
Single-Family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: unpaid principal balance	188,228		167,582
Individually impaired loans with related allowance recorded: total recorded investment	178,048	[1]	156,821	[1]
Related allowance for loan losses	44,545	[2]	46,139	[2]
Individually impaired loans with no related allowance recorded: unpaid principal balance	21,538	[4]	13,131	[4]
Individually impaired loans with no related allowance recorded: total recorded investment	17,804	[1],[4]	8,393	[1],[4]
Table Footnote [Abstract]
Troubled debt restructuring recorded investment	193,400		161,900
Single-Family [Member] | Interest Receivable [Member]
Financing Receivable, Impaired [Line Items]
Related allowance for loan losses	985		1,049
Multifamily [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: unpaid principal balance	2,449		2,832
Individually impaired loans with related allowance recorded: total recorded investment	2,471	[1]	2,855	[1]
Related allowance for loan losses	489	[2]	718	[2]
Individually impaired loans with no related allowance recorded: unpaid principal balance	2,056	[4]	1,759	[4]
Individually impaired loans with no related allowance recorded: total recorded investment	2,068	[1],[4]	1,771	[1],[4]
Table Footnote [Abstract]
Troubled debt restructuring recorded investment	1,100		956
Multifamily [Member] | Interest Receivable [Member]
Financing Receivable, Impaired [Line Items]
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	132,754	[5]	116,825	[5]
Individually impaired loans with related allowance recorded: total recorded investment	126,106	[1],[5]	109,684	[1],[5]
Related allowance for loan losses	28,610	[5]	29,598	[5]
Individually impaired loans with no related allowance recorded: unpaid principal balance	16,222	[4],[5]	9,370	[4],[5]
Individually impaired loans with no related allowance recorded: total recorded investment	13,901	[1],[4],[5]	6,471	[1],[4],[5]
Primary [Member] | Single-Family [Member] | Interest Receivable [Member]
Financing Receivable, Impaired [Line Items]
Related allowance for loan losses	628	[5]	674	[5]
Government [Member] | Single-Family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: unpaid principal balance	214	[6]	258	[6]
Individually impaired loans with related allowance recorded: total recorded investment	208	[1],[6]	258	[1],[6]
Related allowance for loan losses	38	[6]	67	[6]
Individually impaired loans with no related allowance recorded: unpaid principal balance	104	[4],[6]	25	[4],[6]
Individually impaired loans with no related allowance recorded: total recorded investment	104	[1],[4],[6]	17	[1],[4],[6]
Government [Member] | Single-Family [Member] | Interest Receivable [Member]
Financing Receivable, Impaired [Line Items]
Related allowance for loan losses	4	[6]	8	[6]
Alt-A [Member] | Single-Family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: unpaid principal balance	38,387		34,318
Individually impaired loans with related allowance recorded: total recorded investment	35,620	[1]	31,516	[1]
Related allowance for loan losses	11,154		11,121
Individually impaired loans with no related allowance recorded: unpaid principal balance	3,994	[4]	3,056	[4]
Individually impaired loans with no related allowance recorded: total recorded investment	2,822	[1],[4]	1,538	[1],[4]
Alt-A [Member] | Single-Family [Member] | Interest Receivable [Member]
Financing Receivable, Impaired [Line Items]
Related allowance for loan losses	267		268
Other [Member] | Single-Family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: unpaid principal balance	16,873	[7]	16,181	[7]
Individually impaired loans with related allowance recorded: total recorded investment	16,114	[1],[7]	15,363	[1],[7]
Related allowance for loan losses	4,743	[7]	5,353	[7]
Individually impaired loans with no related allowance recorded: unpaid principal balance	1,218	[4],[7]	680	[4],[7]
Individually impaired loans with no related allowance recorded: total recorded investment	977	[1],[4],[7]	367	[1],[4],[7]
Other [Member] | Single-Family [Member] | Interest Receivable [Member]
Financing Receivable, Impaired [Line Items]
Related allowance for loan losses	$ 86	[7]	$ 99	[7]

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

[2] Includes acquired credit-impaired loans.

[3] Includes single-family loans restructured in a TDR with a recorded investment of $193.4 billion and $161.9 billion as of December 31, 2012 and 2011, respectively. Includes multifamily loans restructured in a TDR with a recorded investment of $1.1 billion and $956 million as of December 31, 2012 and 2011, respectively.

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

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

[6] 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.

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