Mortgage Loans Loans in Mortgage Portfolio (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Jun. 30, 2012	Dec. 31, 2011	Sep. 30, 2011		Jun. 30, 2011	Dec. 31, 2010
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	$ 2,983,112			$ 2,966,927
Cost basis and fair value adjustments, net	22,796			3,850
Allowance for loan losses for loans held for investment	(63,012)	[1],[2]	(63,375)	(72,156)	(71,435)	[1]	(69,506)	(61,556)
Total mortgage loans	2,942,896			2,898,621
Single-Family [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	2,798,834			2,790,029
Multifamily [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	184,278			176,898
Fannie Mae [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	378,501			396,522
Cost basis and fair value adjustments, net	(15,042)			(16,143)
Allowance for loan losses for loans held for investment	(54,214)		(52,082)	(57,309)	(55,398)		(55,966)	(48,530)
Total mortgage loans	309,245			323,070
Fannie Mae [Member] | Single-Family [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	312,824			319,496
Fannie Mae [Member] | Multifamily [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	65,677			77,026
Consolidated Trusts [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	2,604,611			2,570,405
Cost basis and fair value adjustments, net	37,838			19,993
Allowance for loan losses for loans held for investment	(8,798)		(11,293)	(14,847)	(16,037)		(13,540)	(13,026)
Total mortgage loans	2,633,651			2,575,551
Consolidated Trusts [Member] | Single-Family [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	2,486,010			2,470,533
Consolidated Trusts [Member] | Multifamily [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	$ 118,601			$ 99,872

[1] Total allowance for loan losses includes $376 million and $334 million as of September 30, 2012 and 2011, respectively, for acquired credit-impaired loans.

[2] As of September 30, 2012, we began classifying as TDRs loans to certain borrowers who have received bankruptcy relief. These loans had a recorded investment of $22.9 billion and a related allowance of $1.1 billion as of September 30, 2012.