Investments in Securities Maturity Information (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	$ 34,073	[1]	$ 35,690	[1]
Available-for-sale, at fair value	37,128		38,171
One Year or Less, Amortized Cost	33
One Year or Less, Fair Value	34
After One Year through Five Years, Amortized Cost	2,277
After One Year through Five Years, Fair Value	2,400
After Five Years through Ten Years, Amortized Cost	1,625
After Five Years through Ten Years, Fair Value	1,716
After Ten Years, Amortized Cost	30,138
After Ten Years, Fair Value	32,978
Fannie Mae [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	5,901	[1]	6,227	[1]
Available-for-sale, at fair value	6,255		6,573
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year through Five Years, Amortized Cost	311
After One Year through Five Years, Fair Value	329
After Five Years through Ten Years, Amortized Cost	345
After Five Years through Ten Years, Fair Value	371
After Ten Years, Amortized Cost	5,245
After Ten Years, Fair Value	5,555
Freddie Mac [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	6,048	[1]	6,365	[1]
Available-for-sale, at fair value	6,515		6,842
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year through Five Years, Amortized Cost	328
After One Year through Five Years, Fair Value	348
After Five Years through Ten Years, Amortized Cost	632
After Five Years through Ten Years, Fair Value	685
After Ten Years, Amortized Cost	5,088
After Ten Years, Fair Value	5,482
Ginnie Mae [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	486	[1]	512	[1]
Available-for-sale, at fair value	557		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	52
After Five Years through Ten Years, Fair Value	59
After Ten Years, Amortized Cost	434
After Ten Years, Fair Value	498
Alt-A private-label securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	6,107	[1]	6,240	[1]
Available-for-sale, at fair value	7,346		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	6,107
After Ten Years, Fair Value	7,346
Subprime private-label securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	5,975	[1]	6,232	[1]
Available-for-sale, at fair value	7,030		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	5,975
After Ten Years, Fair Value	7,030
CMBS [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	1,490	[1]	1,526	[1]
Available-for-sale, at fair value	1,569		1,606
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year through Five Years, Amortized Cost	1,402
After One Year through Five Years, Fair Value	1,479
After Five Years through Ten Years, Amortized Cost	0
After Five Years through Ten Years, Fair Value	0
After Ten Years, Amortized Cost	88
After Ten Years, Fair Value	90
Mortgage revenue bonds [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	5,205	[1]	5,645	[1]
Available-for-sale, at fair value	5,008		5,256
One Year or Less, Amortized Cost	33
One Year or Less, Fair Value	34
After One Year through Five Years, Amortized Cost	236
After One Year through Five Years, Fair Value	240
After Five Years through Ten Years, Amortized Cost	558
After Five Years through Ten Years, Fair Value	561
After Ten Years, Amortized Cost	4,378
After Ten Years, Fair Value	4,173
Other mortgage-related securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	2,861	[1]	2,943	[1]
Available-for-sale, at fair value	2,848		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	4
After Five Years through Ten Years, Amortized Cost	38
After Five Years through Ten Years, Fair Value	40
After Ten Years, Amortized Cost	2,823
After Ten Years, Fair Value	$ 2,804

[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.