Mortgage Loans Loans in Mortgage Portfolio (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	$ 2,978,693	$ 2,966,927
Cost basis and fair value adjustments, net	29,508	3,850
Allowance for loan losses for loans held for investment	(58,795)	(72,156)	(61,556)	(9,925)
Total mortgage loans	2,949,406	2,898,621
Single-Family [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	2,790,276	2,790,029
Multifamily [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	188,417	176,898
Fannie Mae [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	370,741	396,522
Cost basis and fair value adjustments, net	(14,805)	(16,143)
Allowance for loan losses for loans held for investment	(50,519)	(57,309)	(48,530)	(8,078)
Total mortgage loans	305,417	323,070
Fannie Mae [Member] | Single-Family [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	309,277	319,496
Fannie Mae [Member] | Multifamily [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	61,464	77,026
Consolidated Trusts [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	2,607,952	2,570,405
Cost basis and fair value adjustments, net	44,313	19,993
Allowance for loan losses for loans held for investment	(8,276)	(14,847)	(13,026)	(1,847)
Total mortgage loans	2,643,989	2,575,551
Consolidated Trusts [Member] | Single-Family [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	2,480,999	2,470,533
Consolidated Trusts [Member] | Multifamily [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	$ 126,953	$ 99,872