Mortgage Loans Individually Impaired Loans - 2 (Details) (USD $)	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012		Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	$ 179,683,000,000		$ 160,048,000,000		$ 179,754,000,000		$ 159,776,000,000
Individually impaired loans with related allowance recorded: total interest income recognized	1,514,000,000	[1]	1,367,000,000	[1]	3,036,000,000	[1]	2,737,000,000	[1]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	203,000,000		201,000,000		429,000,000		431,000,000
Individually impaired loans with no related allowance recorded: average recorded investment	14,712,000,000	[2]	11,238,000,000	[2]	15,318,000,000	[2]	10,861,000,000	[2]
Individually impaired loans with no related allowance recorded: total interest income recognized	388,000,000	[1],[2]	361,000,000	[1],[2]	1,291,000,000	[1],[2]	638,000,000	[1],[2]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	74,000,000	[2]	80,000,000	[2]	149,000,000	[2]	157,000,000	[2]
Individually impaired loans: average recorded investment	194,395,000,000	[3]	171,286,000,000	[3]	195,072,000,000	[3]	170,637,000,000	[3]
Individually impaired loans: total interest income recognized	1,902,000,000	[1],[3]	1,728,000,000	[1],[3]	4,327,000,000	[1],[3]	3,375,000,000	[1],[3]
Individually impaired loans: interest income recognized on a cash basis	277,000,000	[3]	281,000,000	[3]	578,000,000	[3]	588,000,000	[3]
Single-Family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	176,979,000,000		157,549,000,000		177,126,000,000		157,156,000,000
Individually impaired loans with related allowance recorded: total interest income recognized	1,478,000,000	[1]	1,333,000,000	[1]	2,969,000,000	[1]	2,672,000,000	[1]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	202,000,000		200,000,000		428,000,000		430,000,000
Individually impaired loans with no related allowance recorded: average recorded investment	13,046,000,000	[2]	9,526,000,000	[2]	13,518,000,000	[2]	9,129,000,000	[2]
Individually impaired loans with no related allowance recorded: total interest income recognized	363,000,000	[1],[2]	335,000,000	[1],[2]	1,244,000,000	[1],[2]	591,000,000	[1],[2]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	74,000,000	[2]	80,000,000	[2]	148,000,000	[2]	156,000,000	[2]
Individually impaired loans: total interest income recognized	1,800,000,000		1,700,000,000		4,200,000,000		3,300,000,000
Table Footnote [Abstract]
Troubled debt restructuring recorded investment	188,400,000,000				188,400,000,000				193,400,000,000
Individually impaired loans: contractual interest income	1,400,000,000		1,200,000,000		2,900,000,000		2,400,000,000
Individually impaired loans: effective yield adjustments	410,000,000		436,000,000		1,300,000,000		823,000,000
Multifamily [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	2,704,000,000		2,499,000,000		2,628,000,000		2,620,000,000
Individually impaired loans with related allowance recorded: total interest income recognized	36,000,000	[1]	34,000,000	[1]	67,000,000	[1]	65,000,000	[1]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	1,000,000		1,000,000		1,000,000		1,000,000
Individually impaired loans with no related allowance recorded: average recorded investment	1,666,000,000	[2]	1,712,000,000	[2]	1,800,000,000	[2]	1,732,000,000	[2]
Individually impaired loans with no related allowance recorded: total interest income recognized	25,000,000	[1],[2]	26,000,000	[1],[2]	47,000,000	[1],[2]	47,000,000	[1],[2]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	0	[2]	0	[2]	1,000,000	[2]	1,000,000	[2]
Table Footnote [Abstract]
Troubled debt restructuring recorded investment	1,200,000,000				1,200,000,000				1,100,000,000
Primary [Member] | Single-Family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	125,689,000,000	[4]	110,527,000,000	[4]	125,663,000,000	[4]	110,154,000,000	[4]
Individually impaired loans with related allowance recorded: total interest income recognized	1,093,000,000	[1],[4]	967,000,000	[1],[4]	2,195,000,000	[1],[4]	1,940,000,000	[1],[4]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	152,000,000	[4]	149,000,000	[4]	325,000,000	[4]	322,000,000	[4]
Individually impaired loans with no related allowance recorded: average recorded investment	10,301,000,000	[2],[4]	7,367,000,000	[2],[4]	10,688,000,000	[2],[4]	7,053,000,000	[2],[4]
Individually impaired loans with no related allowance recorded: total interest income recognized	283,000,000	[1],[2],[4]	254,000,000	[1],[2],[4]	924,000,000	[1],[2],[4]	438,000,000	[1],[2],[4]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	57,000,000	[2],[4]	61,000,000	[2],[4]	116,000,000	[2],[4]	115,000,000	[2],[4]
Government [Member] | Single-Family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	214,000,000	[5]	204,000,000	[5]	211,000,000	[5]	227,000,000	[5]
Individually impaired loans with related allowance recorded: total interest income recognized	2,000,000	[1],[5]	3,000,000	[1],[5]	5,000,000	[1],[5]	6,000,000	[1],[5]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	0	[5]	0	[5]	0	[5]	0	[5]
Individually impaired loans with no related allowance recorded: average recorded investment	112,000,000	[2],[5]	88,000,000	[2],[5]	110,000,000	[2],[5]	58,000,000	[2],[5]
Individually impaired loans with no related allowance recorded: total interest income recognized	2,000,000	[1],[2],[5]	1,000,000	[1],[2],[5]	4,000,000	[1],[2],[5]	3,000,000	[1],[2],[5]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	0	[2],[5]	0	[2],[5]	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	35,376,000,000		31,600,000,000		35,422,000,000		31,543,000,000
Individually impaired loans with related allowance recorded: total interest income recognized	275,000,000	[1]	253,000,000	[1]	552,000,000	[1]	506,000,000	[1]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	35,000,000		35,000,000		74,000,000		74,000,000
Individually impaired loans with no related allowance recorded: average recorded investment	1,972,000,000	[2]	1,672,000,000	[2]	2,049,000,000	[2]	1,628,000,000	[2]
Individually impaired loans with no related allowance recorded: total interest income recognized	55,000,000	[1],[2]	60,000,000	[1],[2]	230,000,000	[1],[2]	111,000,000	[1],[2]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	12,000,000	[2]	13,000,000	[2]	22,000,000	[2]	28,000,000	[2]
Other [Member] | Single-Family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	15,700,000,000	[6]	15,218,000,000	[6]	15,830,000,000	[6]	15,232,000,000	[6]
Individually impaired loans with related allowance recorded: total interest income recognized	108,000,000	[1],[6]	110,000,000	[1],[6]	217,000,000	[1],[6]	220,000,000	[1],[6]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	15,000,000	[6]	16,000,000	[6]	29,000,000	[6]	34,000,000	[6]
Individually impaired loans with no related allowance recorded: average recorded investment	661,000,000	[2],[6]	399,000,000	[2],[6]	671,000,000	[2],[6]	390,000,000	[2],[6]
Individually impaired loans with no related allowance recorded: total interest income recognized	23,000,000	[1],[2],[6]	20,000,000	[1],[2],[6]	86,000,000	[1],[2],[6]	39,000,000	[1],[2],[6]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	$ 5,000,000	[2],[6]	$ 6,000,000	[2],[6]	$ 10,000,000	[2],[6]	$ 13,000,000	[2],[6]

[1] Total single-family interest income recognized of $1.8 billion and $1.7 billion for the three months ended June 30, 2013 and 2012, respectively, consists of $1.4 billion and $1.2 billion of contractual interest and $410 million and $436 million of effective yield adjustments. Total single-family interest income recognized of $4.2 billion and $3.3 billion for the six months ended June 30, 2013 and 2012, respectively, consists of $2.9 billion and $2.4 billion of contractual interest and $1.3 billion and $823 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 $188.4 billion and $193.4 billion as of June 30, 2013 and December 31, 2012, respectively. Includes multifamily loans restructured in a TDR with a recorded investment of $1.2 billion and $1.1 billion as of June 30, 2013 and December 31, 2012, respectively.

[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.