Mortgage Loans Loans in Mortgage Portfolio (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	$ 2,983,099	$ 2,978,693
Cost basis and fair value adjustments, net	31,998	29,508
Allowance for loan losses for loans held for investment	(56,461)	(58,795)	(70,109)	(72,156)
Total mortgage loans	2,958,636	2,949,406
Single-Family [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	2,795,363	2,790,276
Multifamily [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	187,736	188,417
Fannie Mae [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	351,305	370,741
Cost basis and fair value adjustments, net	(14,369)	(14,805)
Allowance for loan losses for loans held for investment	(49,553)	(50,519)	(57,001)	(57,309)
Total mortgage loans	287,383	305,417
Fannie Mae [Member] | Single-Family [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	297,066	309,277
Fannie Mae [Member] | Multifamily [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	54,239	61,464
Consolidated Trusts [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	2,631,794	2,607,952
Cost basis and fair value adjustments, net	46,367	44,313
Allowance for loan losses for loans held for investment	(6,908)	(8,276)	(13,108)	(14,847)
Total mortgage loans	2,671,253	2,643,989
Consolidated Trusts [Member] | Single-Family [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	2,498,297	2,480,999
Consolidated Trusts [Member] | Multifamily [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	$ 133,497	$ 126,953