Investments in Securities Maturity Information (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	$ 38,767	[1]	$ 61,766	[1]
Available-for-sale, at fair value	41,000		63,181
One Year or Less, Amortized Cost	34
One Year or Less, Fair Value	36
After One Year through Five Years, Amortized Cost	3,455
After One Year through Five Years, Fair Value	3,631
After Five Years through Ten Years, Amortized Cost	1,837
After Five Years through Ten Years, Fair Value	1,933
After Ten Years, Amortized Cost	33,441
After Ten Years, Fair Value	35,400
Fannie Mae [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	6,800	[1]	9,580	[1]
Available-for-sale, at fair value	7,199
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	488
After Five Years through Ten Years, Fair Value	523
After Ten Years, Amortized Cost	5,991
After Ten Years, Fair Value	6,337
Freddie Mac [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	6,755	[1]	8,652	[1]
Available-for-sale, at fair value	7,264		9,380
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year through Five Years, Amortized Cost	310
After One Year through Five Years, Fair Value	329
After Five Years through Ten Years, Amortized Cost	710
After Five Years through Ten Years, Fair Value	763
After Ten Years, Amortized Cost	5,735
After Ten Years, Fair Value	6,172
Ginnie Mae [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	543	[1]	645	[1]
Available-for-sale, at fair value	625		751
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year through Five Years, Amortized Cost	1
After One Year through Five Years, Fair Value	1
After Five Years through Ten Years, Amortized Cost	22
After Five Years through Ten Years, Fair Value	26
After Ten Years, Amortized Cost	520
After Ten Years, Fair Value	598
Alt-A private-label securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	6,445	[1]	11,356	[1]
Available-for-sale, at fair value	7,399		11,075
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year through Five Years, Amortized Cost	1
After One Year through Five Years, Fair Value	1
After Five Years through Ten Years, Amortized Cost	0
After Five Years through Ten Years, Fair Value	0
After Ten Years, Amortized Cost	6,444
After Ten Years, Fair Value	7,398
Subprime private-label securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	6,418	[1]	8,137	[1]
Available-for-sale, at fair value	6,965		7,447
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	6,418
After Ten Years, Fair Value	6,965
CMBS [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	2,651	[1]	12,284	[1]
Available-for-sale, at fair value	2,783		13,097
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year through Five Years, Amortized Cost	2,543
After One Year through Five Years, Fair Value	2,672
After Five Years through Ten Years, Amortized Cost	0
After Five Years through Ten Years, Fair Value	0
After Ten Years, Amortized Cost	108
After Ten Years, Fair Value	111
Mortgage revenue bonds [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	6,107	[1]	7,782	[1]
Available-for-sale, at fair value	5,802		7,842
One Year or Less, Amortized Cost	34
One Year or Less, Fair Value	36
After One Year through Five Years, Amortized Cost	279
After One Year through Five Years, Fair Value	284
After Five Years through Ten Years, Amortized Cost	577
After Five Years through Ten Years, Fair Value	580
After Ten Years, Amortized Cost	5,217
After Ten Years, Fair Value	4,902
Other mortgage-related securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	3,048	[1]	3,330	[1]
Available-for-sale, at fair value	2,963		3,154
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	5
After Five Years through Ten Years, Amortized Cost	40
After Five Years through Ten Years, Fair Value	41
After Ten Years, Amortized Cost	3,008
After Ten Years, Fair Value	$ 2,917

[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.