Mortgage Loans Individually Impaired Loans - 2 (Details) (USD $)	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012		Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	$ 180,301,000,000		$ 159,667,000,000
Individually impaired loans with related allowance recorded: total interest income recognized	1,522,000,000	[1]	1,370,000,000	[1]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	226,000,000		230,000,000
Individually impaired loans with no related allowance recorded: average recorded investment	15,365,000,000	[2]	10,274,000,000	[2]
Individually impaired loans with no related allowance recorded: total interest income recognized	903,000,000	[1],[2]	277,000,000	[1],[2]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	75,000,000	[2]	77,000,000	[2]
Individually impaired loans: average recorded investment	195,666,000,000	[3]	169,941,000,000	[3]
Individually impaired loans: total interest income recognized	2,425,000,000	[1]	1,647,000,000	[1]
Individually impaired loans: interest income recognized on a cash basis	301,000,000		307,000,000
Single-Family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	177,694,000,000		156,994,000,000
Individually impaired loans with related allowance recorded: total interest income recognized	1,491,000,000	[1]	1,339,000,000	[1]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	226,000,000		230,000,000
Individually impaired loans with no related allowance recorded: average recorded investment	13,679,000,000	[2]	8,560,000,000	[2]
Individually impaired loans with no related allowance recorded: total interest income recognized	881,000,000	[1],[2]	256,000,000	[1],[2]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	74,000,000	[2]	76,000,000	[2]
Individually impaired loans: total interest income recognized	2,400,000,000		1,600,000,000
Troubled debt restructuring recorded investment	189,200,000,000				193,400,000,000
Individually impaired loans: contractual interest income	1,400,000,000		1,200,000,000
Individually impaired loans: effective yield adjustments	941,000,000		387,000,000
Multifamily [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	2,607,000,000		2,673,000,000
Individually impaired loans with related allowance recorded: total interest income recognized	31,000,000	[1]	31,000,000	[1]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	0		0
Individually impaired loans with no related allowance recorded: average recorded investment	1,686,000,000	[2]	1,714,000,000	[2]
Individually impaired loans with no related allowance recorded: total interest income recognized	22,000,000	[1],[2]	21,000,000	[1],[2]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	1,000,000	[2]	1,000,000	[2]
Troubled debt restructuring recorded investment	1,100,000,000				1,100,000,000
Primary [Member] | Single-Family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	125,968,000,000	[4]	109,970,000,000	[4]
Individually impaired loans with related allowance recorded: total interest income recognized	1,102,000,000	[1],[4]	973,000,000	[1],[4]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	173,000,000	[4]	173,000,000	[4]
Individually impaired loans with no related allowance recorded: average recorded investment	10,830,000,000	[2],[4]	6,608,000,000	[2],[4]
Individually impaired loans with no related allowance recorded: total interest income recognized	641,000,000	[1],[2],[4]	184,000,000	[1],[2],[4]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	59,000,000	[2],[4]	54,000,000	[2],[4]
Government [Member] | Single-Family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	208,000,000	[5]	260,000,000	[5]
Individually impaired loans with related allowance recorded: total interest income recognized	3,000,000	[1],[5]	3,000,000	[1],[5]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	0	[5]	0	[5]
Individually impaired loans with no related allowance recorded: average recorded investment	109,000,000	[2],[5]	20,000,000	[2],[5]
Individually impaired loans with no related allowance recorded: total interest income recognized	2,000,000	[1],[2],[5]	2,000,000	[1],[2],[5]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	0	[2],[5]	0	[2],[5]
Alt-A [Member] | Single-Family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	35,534,000,000		31,509,000,000
Individually impaired loans with related allowance recorded: total interest income recognized	277,000,000	[1]	253,000,000	[1]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	39,000,000		39,000,000
Individually impaired loans with no related allowance recorded: average recorded investment	2,078,000,000	[2]	1,558,000,000	[2]
Individually impaired loans with no related allowance recorded: total interest income recognized	175,000,000	[1],[2]	51,000,000	[1],[2]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	10,000,000	[2]	15,000,000	[2]
Other [Member] | Single-Family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	15,984,000,000	[6]	15,255,000,000	[6]
Individually impaired loans with related allowance recorded: total interest income recognized	109,000,000	[1],[6]	110,000,000	[1],[6]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	14,000,000	[6]	18,000,000	[6]
Individually impaired loans with no related allowance recorded: average recorded investment	662,000,000	[2],[6]	374,000,000	[2],[6]
Individually impaired loans with no related allowance recorded: total interest income recognized	63,000,000	[1],[2],[6]	19,000,000	[1],[2],[6]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	$ 5,000,000	[2],[6]	$ 7,000,000	[2],[6]

[1] Total single-family interest income recognized of $2.4 billion and $1.6 billion for the three months ended March 31, 2013 and 2012, respectively, consists of $1.4 billion and $1.2 billion of contractual interest and $941 million and $387 million of effective yield adjustments.

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

[3] Includes single-family loans restructured in a TDR with a recorded investment of $189.2 billion and $193.4 billion as of March 31, 2013 and December 31, 2012, respectively. Includes multifamily loans restructured in a TDR with a recorded investment of $1.1 billion as of March 31, 2013 and December 31, 2012.

[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.