Mortgage Loans Individually Impaired Loans - 2 (Details) (USD $)	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012		Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	$ 176,883,000,000		$ 166,057,000,000		$ 178,763,000,000		$ 162,219,000,000
Individually impaired loans with related allowance recorded: total interest income recognized	1,494,000,000	[1]	1,417,000,000	[1]	4,530,000,000	[1]	4,154,000,000	[1]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	184,000,000		208,000,000		613,000,000		639,000,000
Individually impaired loans with no related allowance recorded: average recorded investment	17,330,000,000	[2]	12,817,000,000	[2]	15,964,000,000	[2]	11,466,000,000	[2]
Individually impaired loans with no related allowance recorded: total interest income recognized	341,000,000	[1],[2]	374,000,000	[1],[2]	1,632,000,000	[1],[2]	1,012,000,000	[1],[2]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	75,000,000	[2]	79,000,000	[2]	224,000,000	[2]	236,000,000	[2]
Individually impaired loans: average recorded investment	194,213,000,000	[3]	178,874,000,000	[3]	194,727,000,000	[3]	173,685,000,000	[3]
Individually impaired loans: total interest income recognized	1,835,000,000	[1],[3]	1,791,000,000	[1],[3]	6,162,000,000	[1],[3]	5,166,000,000	[1],[3]
Individually impaired loans: interest income recognized on a cash basis	259,000,000	[3]	287,000,000	[3]	837,000,000	[3]	875,000,000	[3]
Single-Family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	174,250,000,000		163,637,000,000		176,142,000,000		159,668,000,000
Individually impaired loans with related allowance recorded: total interest income recognized	1,462,000,000	[1]	1,386,000,000	[1]	4,431,000,000	[1]	4,058,000,000	[1]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	184,000,000		207,000,000		612,000,000		637,000,000
Individually impaired loans with no related allowance recorded: average recorded investment	15,328,000,000	[2]	11,119,000,000	[2]	14,121,000,000	[2]	9,759,000,000	[2]
Individually impaired loans with no related allowance recorded: total interest income recognized	316,000,000	[1],[2]	351,000,000	[1],[2]	1,560,000,000	[1],[2]	942,000,000	[1],[2]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	73,000,000	[2]	79,000,000	[2]	221,000,000	[2]	235,000,000	[2]
Individually impaired loans: total interest income recognized	1,800,000,000		1,700,000,000		6,000,000,000		5,000,000,000
Table Footnote [Abstract]
Troubled debt restructuring recorded investment	188,200,000,000				188,200,000,000				193,400,000,000
Individually impaired loans: contractual interest income	1,400,000,000		1,300,000,000		4,300,000,000		3,700,000,000
Individually impaired loans: effective yield adjustments	355,000,000		444,000,000		1,700,000,000		1,300,000,000
Single-Family [Member] | Primary [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	123,818,000,000	[4]	115,042,000,000	[4]	125,026,000,000	[4]	112,050,000,000	[4]
Individually impaired loans with related allowance recorded: total interest income recognized	1,081,000,000	[1],[4]	1,014,000,000	[1],[4]	3,276,000,000	[1],[4]	2,954,000,000	[1],[4]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	141,000,000	[4]	157,000,000	[4]	466,000,000	[4]	479,000,000	[4]
Individually impaired loans with no related allowance recorded: average recorded investment	12,067,000,000	[2],[4]	8,709,000,000	[2],[4]	11,148,000,000	[2],[4]	7,579,000,000	[2],[4]
Individually impaired loans with no related allowance recorded: total interest income recognized	243,000,000	[1],[2],[4]	267,000,000	[1],[2],[4]	1,167,000,000	[1],[2],[4]	705,000,000	[1],[2],[4]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	58,000,000	[2],[4]	59,000,000	[2],[4]	174,000,000	[2],[4]	174,000,000	[2],[4]
Single-Family [Member] | Government [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	215,000,000	[5]	197,000,000	[5]	213,000,000	[5]	220,000,000	[5]
Individually impaired loans with related allowance recorded: total interest income recognized	3,000,000	[1],[5]	3,000,000	[1],[5]	8,000,000	[1],[5]	9,000,000	[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	114,000,000	[2],[5]	102,000,000	[2],[5]	111,000,000	[2],[5]	71,000,000	[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]	6,000,000	[1],[2],[5]	5,000,000	[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]
Single-Family [Member] | Alt-A [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	34,865,000,000		32,875,000,000		35,231,000,000		32,050,000,000
Individually impaired loans with related allowance recorded: total interest income recognized	274,000,000	[1]	259,000,000	[1]	826,000,000	[1]	765,000,000	[1]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	31,000,000		35,000,000		105,000,000		109,000,000
Individually impaired loans with no related allowance recorded: average recorded investment	2,332,000,000	[2]	1,865,000,000	[2]	2,145,000,000	[2]	1,703,000,000	[2]
Individually impaired loans with no related allowance recorded: total interest income recognized	52,000,000	[1],[2]	61,000,000	[1],[2]	282,000,000	[1],[2]	172,000,000	[1],[2]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	11,000,000	[2]	14,000,000	[2]	33,000,000	[2]	42,000,000	[2]
Single-Family [Member] | Other [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	15,352,000,000	[6]	15,523,000,000	[6]	15,672,000,000	[6]	15,348,000,000	[6]
Individually impaired loans with related allowance recorded: total interest income recognized	104,000,000	[1],[6]	110,000,000	[1],[6]	321,000,000	[1],[6]	330,000,000	[1],[6]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	12,000,000	[6]	15,000,000	[6]	41,000,000	[6]	49,000,000	[6]
Individually impaired loans with no related allowance recorded: average recorded investment	815,000,000	[2],[6]	443,000,000	[2],[6]	717,000,000	[2],[6]	406,000,000	[2],[6]
Individually impaired loans with no related allowance recorded: total interest income recognized	19,000,000	[1],[2],[6]	21,000,000	[1],[2],[6]	105,000,000	[1],[2],[6]	60,000,000	[1],[2],[6]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	4,000,000	[2],[6]	6,000,000	[2],[6]	14,000,000	[2],[6]	19,000,000	[2],[6]
Multifamily [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	2,633,000,000		2,420,000,000		2,621,000,000		2,551,000,000
Individually impaired loans with related allowance recorded: total interest income recognized	32,000,000	[1]	31,000,000	[1]	99,000,000	[1]	96,000,000	[1]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	0		1,000,000		1,000,000		2,000,000
Individually impaired loans with no related allowance recorded: average recorded investment	2,002,000,000	[2]	1,698,000,000	[2]	1,843,000,000	[2]	1,707,000,000	[2]
Individually impaired loans with no related allowance recorded: total interest income recognized	25,000,000	[1],[2]	23,000,000	[1],[2]	72,000,000	[1],[2]	70,000,000	[1],[2]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	2,000,000	[2]	0	[2]	3,000,000	[2]	1,000,000	[2]
Table Footnote [Abstract]
Troubled debt restructuring recorded investment	$ 904,000,000				$ 904,000,000				$ 1,100,000,000

[1] Total single-family interest income recognized of $1.8 billion and $1.7 billion for the three months ended September 30, 2013 and 2012, respectively, consists of $1.4 billion and $1.3 billion of contractual interest and $355 million and $444 million of effective yield adjustments. Total single-family interest income recognized of $6.0 billion and $5.0 billion for the nine months ended September 30, 2013 and 2012, respectively, consists of $4.3 billion and $3.7 billion of contractual interest and $1.7 billion and $1.3 billion 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 $188.2 billion and $193.4 billion as of September 30, 2013 and December 31, 2012, respectively. Includes multifamily loans restructured in a TDR with a recorded investment of $904 million and $1.1 billion as of September 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.