Mortgage Loans Loans in Mortgage Portfolio (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	$ 2,992,912		$ 2,978,693
Cost basis and fair value adjustments, net	32,785		29,508
Allowance for loan losses for loans held for investment	(49,643)	(56,461)	(58,795)	(63,375)	(70,109)	(72,156)
Total mortgage loans	2,976,054		2,949,406
Single-Family [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	2,804,617		2,790,276
Multifamily [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	188,295		188,417
Fannie Mae [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	343,292		370,741
Cost basis and fair value adjustments, net	(14,275)		(14,805)
Allowance for loan losses for loans held for investment	(44,825)	(49,553)	(50,519)	(52,082)	(57,001)	(57,309)
Total mortgage loans	284,192		305,417
Fannie Mae [Member] | Single-Family [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	293,790		309,277
Fannie Mae [Member] | Multifamily [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	49,502		61,464
Consolidated Trusts [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	2,649,620		2,607,952
Cost basis and fair value adjustments, net	47,060		44,313
Allowance for loan losses for loans held for investment	(4,818)	(6,908)	(8,276)	(11,293)	(13,108)	(14,847)
Total mortgage loans	2,691,862		2,643,989
Consolidated Trusts [Member] | Single-Family [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	2,510,827		2,480,999
Consolidated Trusts [Member] | Multifamily [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	$ 138,793		$ 126,953