Mortgage Loans Individually Impaired Loans - 2 (Details) (USD $)	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011		Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	$ 166,057,000,000		$ 149,705,000,000		$ 162,219,000,000		$ 145,843,000,000
Individually impaired loans with related allowance recorded: total interest income recognized	1,417,000,000	[1]	1,336,000,000	[1]	4,154,000,000	[1]	3,898,000,000	[1]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	208,000,000		252,000,000		639,000,000		767,000,000
Individually impaired loans with no related allowance recorded: average recorded investment	12,817,000,000	[2]	10,290,000,000	[2]	11,466,000,000	[2]	8,678,000,000	[2]
Individually impaired loans with no related allowance recorded: total interest income recognized	374,000,000	[1],[2]	275,000,000	[1],[2]	1,012,000,000	[1],[2]	663,000,000	[1],[2]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	79,000,000	[2]	87,000,000	[2]	236,000,000	[2]	213,000,000	[2]
Individually impaired loans: average recorded investment	178,874,000,000		159,995,000,000		173,685,000,000		154,521,000,000
Individually impaired loans: total interest income recognized	1,791,000,000	[1]	1,611,000,000	[1]	5,166,000,000	[1]	4,561,000,000	[1]
Individually impaired loans: interest income recognized on a cash basis	287,000,000		339,000,000		875,000,000		980,000,000
Loans Discharged with Bankruptcy Relief [Member]
Financing Receivable, Impaired [Line Items]
Troubled debt restructuring recorded investment	22,900,000,000				22,900,000,000
Troubled debt restructuring, Allowance	1,100,000,000				1,100,000,000
Single-Family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	163,637,000,000		147,220,000,000		159,668,000,000		143,519,000,000
Individually impaired loans with related allowance recorded: total interest income recognized	1,386,000,000	[1]	1,310,000,000	[1]	4,058,000,000	[1]	3,824,000,000	[1]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	207,000,000		250,000,000		637,000,000		762,000,000
Individually impaired loans with no related allowance recorded: average recorded investment	11,119,000,000	[2]	9,454,000,000	[2]	9,759,000,000	[2]	7,879,000,000	[2]
Individually impaired loans with no related allowance recorded: total interest income recognized	351,000,000	[1],[2]	263,000,000	[1],[2]	942,000,000	[1],[2]	626,000,000	[1],[2]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	79,000,000	[2]	85,000,000	[2]	235,000,000	[2]	206,000,000	[2]
Individually impaired loans: total interest income recognized	1,700,000,000		1,600,000,000		5,000,000,000		4,500,000,000
Troubled debt restructuring recorded investment	190,100,000,000				190,100,000,000				161,900,000,000
Individually impaired loans: contractual interest income	1,300,000,000		1,100,000,000		3,700,000,000		3,300,000,000
Individually impaired loans: effective yield adjustments	444,000,000		427,000,000		1,300,000,000		1,200,000,000
Multifamily [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	2,420,000,000		2,485,000,000		2,551,000,000		2,324,000,000
Individually impaired loans with related allowance recorded: total interest income recognized	31,000,000	[1]	26,000,000	[1]	96,000,000	[1]	74,000,000	[1]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	1,000,000		2,000,000		2,000,000		5,000,000
Individually impaired loans with no related allowance recorded: average recorded investment	1,698,000,000	[2]	836,000,000	[2]	1,707,000,000	[2]	799,000,000	[2]
Individually impaired loans with no related allowance recorded: total interest income recognized	23,000,000	[1],[2]	12,000,000	[1],[2]	70,000,000	[1],[2]	37,000,000	[1],[2]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	0	[2]	2,000,000	[2]	1,000,000	[2]	7,000,000	[2]
Troubled debt restructuring recorded investment	1,000,000,000				1,000,000,000				956,000,000
Primary [Member] | Single-Family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	115,042,000,000	[3]	102,555,000,000	[3]	112,050,000,000	[3]	99,495,000,000	[3]
Individually impaired loans with related allowance recorded: total interest income recognized	1,014,000,000	[1],[3]	949,000,000	[1],[3]	2,954,000,000	[1],[3]	2,764,000,000	[1],[3]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	157,000,000	[3]	183,000,000	[3]	479,000,000	[3]	550,000,000	[3]
Individually impaired loans with no related allowance recorded: average recorded investment	8,709,000,000	[2],[3]	7,118,000,000	[2],[3]	7,579,000,000	[2],[3]	6,019,000,000	[2],[3]
Individually impaired loans with no related allowance recorded: total interest income recognized	267,000,000	[1],[2],[3]	175,000,000	[1],[2],[3]	705,000,000	[1],[2],[3]	427,000,000	[1],[2],[3]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	59,000,000	[2],[3]	58,000,000	[2],[3]	174,000,000	[2],[3]	146,000,000	[2],[3]
Government [Member] | Single-Family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	197,000,000	[4]	280,000,000	[4]	220,000,000	[4]	270,000,000	[4]
Individually impaired loans with related allowance recorded: total interest income recognized	3,000,000	[1],[4]	3,000,000	[1],[4]	9,000,000	[1],[4]	9,000,000	[1],[4]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	0	[4]	0	[4]	0	[4]	0	[4]
Individually impaired loans with no related allowance recorded: average recorded investment	102,000,000	[2],[4]	21,000,000	[2],[4]	71,000,000	[2],[4]	14,000,000	[2],[4]
Individually impaired loans with no related allowance recorded: total interest income recognized	2,000,000	[1],[2],[4]	2,000,000	[1],[2],[4]	5,000,000	[1],[2],[4]	6,000,000	[1],[2],[4]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	0	[2],[4]	0	[2],[4]	0	[2],[4]	0	[2],[4]
Alt-A [Member] | Single-Family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	32,875,000,000		29,755,000,000		32,050,000,000		29,459,000,000
Individually impaired loans with related allowance recorded: total interest income recognized	259,000,000	[1]	247,000,000	[1]	765,000,000	[1]	728,000,000	[1]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	35,000,000		45,000,000		109,000,000		143,000,000
Individually impaired loans with no related allowance recorded: average recorded investment	1,865,000,000	[2]	1,832,000,000	[2]	1,703,000,000	[2]	1,443,000,000	[2]
Individually impaired loans with no related allowance recorded: total interest income recognized	61,000,000	[1],[2]	68,000,000	[1],[2]	172,000,000	[1],[2]	154,000,000	[1],[2]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	14,000,000	[2]	21,000,000	[2]	42,000,000	[2]	47,000,000	[2]
Other [Member] | Single-Family [Member]
Financing Receivable, Impaired [Line Items]
Individually impaired loans with related allowance recorded: average recorded investment	15,523,000,000	[5]	14,630,000,000	[5]	15,348,000,000	[5]	14,295,000,000	[5]
Individually impaired loans with related allowance recorded: total interest income recognized	110,000,000	[1],[5]	111,000,000	[1],[5]	330,000,000	[1],[5]	323,000,000	[1],[5]
Individually impaired loans with related allowance recorded: interest income recognized on a cash basis	15,000,000	[5]	22,000,000	[5]	49,000,000	[5]	69,000,000	[5]
Individually impaired loans with no related allowance recorded: average recorded investment	443,000,000	[2],[5]	483,000,000	[2],[5]	406,000,000	[2],[5]	403,000,000	[2],[5]
Individually impaired loans with no related allowance recorded: total interest income recognized	21,000,000	[1],[2],[5]	18,000,000	[1],[2],[5]	60,000,000	[1],[2],[5]	39,000,000	[1],[2],[5]
Individually impaired loans with no related allowance recorded: interest income recognized on a cash basis	$ 6,000,000	[2],[5]	$ 6,000,000	[2],[5]	$ 19,000,000	[2],[5]	$ 13,000,000	[2],[5]

[1] Total single-family interest income recognized of $1.7 billion and $1.6 billion for the three months ended September 30, 2012 and 2011, respectively, consists of $1.3 billion and $1.1 billion of contractual interest and $444 million and $427 million of effective yield adjustments. Total single-family interest income recognized of $5.0 billion and $4.5 billion for the nine months ended September 30, 2012 and 2011, respectively, consists of $3.7 billion and $3.3 billion of contractual interest and $1.3 billion and $1.2 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] Consists of mortgage loans that are not included in other loan classes.

[4] 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.

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