Investments in Securities Maturity Information (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	$ 30,903	[1]	$ 35,690	[1]
Available-for-sale, at fair value	34,026		38,171
One Year or Less, Amortized Cost	26
One Year or Less, Fair Value	27
After One Year through Five Years, Amortized Cost	2,242
After One Year through Five Years, Fair Value	2,367
After Five Years through Ten Years, Amortized Cost	1,443
After Five Years through Ten Years, Fair Value	1,537
After Ten Years, Amortized Cost	27,192
After Ten Years, Fair Value	30,095
Fannie Mae [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	5,663	[1]	6,227	[1]
Available-for-sale, at fair value	6,022		6,573
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year through Five Years, Amortized Cost	321
After One Year through Five Years, Fair Value	339
After Five Years through Ten Years, Amortized Cost	284
After Five Years through Ten Years, Fair Value	307
After Ten Years, Amortized Cost	5,058
After Ten Years, Fair Value	5,376
Freddie Mac [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	5,735	[1]	6,365	[1]
Available-for-sale, at fair value	6,202		6,842
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year through Five Years, Amortized Cost	367
After One Year through Five Years, Fair Value	389
After Five Years through Ten Years, Amortized Cost	590
After Five Years through Ten Years, Fair Value	646
After Ten Years, Amortized Cost	4,778
After Ten Years, Fair Value	5,167
Ginnie Mae [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	461	[1]	512	[1]
Available-for-sale, at fair value	528		588
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year through Five Years, Amortized Cost	0
After One Year through Five Years, Fair Value	0
After Five Years through Ten Years, Amortized Cost	66
After Five Years through Ten Years, Fair Value	75
After Ten Years, Amortized Cost	395
After Ten Years, Fair Value	453
Alt-A private-label securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	5,479	[1]	6,240	[1]
Available-for-sale, at fair value	6,681		7,349
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year through Five Years, Amortized Cost	0
After One Year through Five Years, Fair Value	0
After Five Years through Ten Years, Amortized Cost	0
After Five Years through Ten Years, Fair Value	0
After Ten Years, Amortized Cost	5,479
After Ten Years, Fair Value	6,681
Subprime private-label securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	4,688	[1]	6,232	[1]
Available-for-sale, at fair value	5,705		7,068
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year through Five Years, Amortized Cost	0
After One Year through Five Years, Fair Value	0
After Five Years through Ten Years, Amortized Cost	0
After Five Years through Ten Years, Fair Value	0
After Ten Years, Amortized Cost	4,688
After Ten Years, Fair Value	5,705
CMBS [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	1,427	[1]	1,526	[1]
Available-for-sale, at fair value	1,508		1,606
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year through Five Years, Amortized Cost	1,345
After One Year through Five Years, Fair Value	1,424
After Five Years through Ten Years, Amortized Cost	0
After Five Years through Ten Years, Fair Value	0
After Ten Years, Amortized Cost	82
After Ten Years, Fair Value	84
Mortgage revenue bonds [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	4,669	[1]	5,645	[1]
Available-for-sale, at fair value	4,560		5,256
One Year or Less, Amortized Cost	26
One Year or Less, Fair Value	27
After One Year through Five Years, Amortized Cost	209
After One Year through Five Years, Fair Value	212
After Five Years through Ten Years, Amortized Cost	467
After Five Years through Ten Years, Fair Value	470
After Ten Years, Amortized Cost	3,967
After Ten Years, Fair Value	3,851
Other mortgage-related securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	2,781	[1]	2,943	[1]
Available-for-sale, at fair value	2,820		2,889
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year through Five Years, Amortized Cost	0
After One Year through Five Years, Fair Value	3
After Five Years through Ten Years, Amortized Cost	36
After Five Years through Ten Years, Fair Value	39
After Ten Years, Amortized Cost	2,745
After Ten Years, Fair Value	$ 2,778

[1] Amortized cost consists of unpaid principal balance, unamortized premiums, discounts and other cost basis adjustments as well as net other-than-temporary impairments (“OTTI”) recognized in our condensed consolidated statements of operations and comprehensive income.