Investments in Securities Maturity Information (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	$ 69,905	[1]	$ 78,845	[1]
Available-for-sale, at fair value	69,694		77,582
One Year or Less, Amortized Cost	121
One Year or Less, Fair Value	126
After One Year through Five Years, Amortized Cost	10,000
After One Year through Five Years, Fair Value	10,352
After Five Years through Ten Years, Amortized Cost	6,487
After Five Years through Ten Years, Fair Value	6,769
After Ten Years, Amortized Cost	53,297
After Ten Years, Fair Value	52,447
Fannie Mae [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	12,100	[1]	15,486	[1]
Available-for-sale, at fair value	13,188		16,850
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year through Five Years, Amortized Cost	18
After One Year through Five Years, Fair Value	19
After Five Years through Ten Years, Amortized Cost	1,327
After Five Years through Ten Years, Fair Value	1,409
After Ten Years, Amortized Cost	10,755
After Ten Years, Fair Value	11,760
Freddie Mac [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	10,143	[1]	11,906	[1]
Available-for-sale, at fair value	10,983		12,823
One Year or Less, Amortized Cost	3
One Year or Less, Fair Value	3
After One Year through Five Years, Amortized Cost	51
After One Year through Five Years, Fair Value	55
After Five Years through Ten Years, Amortized Cost	937
After Five Years through Ten Years, Fair Value	1,007
After Ten Years, Amortized Cost	9,152
After Ten Years, Fair Value	9,918
Ginnie Mae [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	710	[1]	775	[1]
Available-for-sale, at fair value	829		902
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year through Five Years, Amortized Cost	2
After One Year through Five Years, Fair Value	2
After Five Years through Ten Years, Amortized Cost	4
After Five Years through Ten Years, Fair Value	4
After Ten Years, Amortized Cost	704
After Ten Years, Fair Value	823
Alt-A private-label securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	12,187	[1]	13,314	[1]
Available-for-sale, at fair value	11,183		11,683
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	204
After Five Years through Ten Years, Fair Value	209
After Ten Years, Amortized Cost	11,982
After Ten Years, Fair Value	10,973
Subprime private-label securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	8,695	[1]	9,556	[1]
Available-for-sale, at fair value	7,230		7,586
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	8,695
After Ten Years, Fair Value	7,230
CMBS [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	13,251	[1],[2]	13,949	[1],[2]
Available-for-sale, at fair value	13,668		14,026
One Year or Less, Amortized Cost	62
One Year or Less, Fair Value	65
After One Year through Five Years, Amortized Cost	9,590
After One Year through Five Years, Fair Value	9,929
After Five Years through Ten Years, Amortized Cost	3,304
After Five Years through Ten Years, Fair Value	3,401
After Ten Years, Amortized Cost	295
After Ten Years, Fair Value	273
Mortgage revenue bonds [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	9,295	[1]	10,172	[1]
Available-for-sale, at fair value	9,357		10,254
One Year or Less, Amortized Cost	56
One Year or Less, Fair Value	58
After One Year through Five Years, Amortized Cost	338
After One Year through Five Years, Fair Value	346
After Five Years through Ten Years, Amortized Cost	711
After Five Years through Ten Years, Fair Value	728
After Ten Years, Amortized Cost	8,190
After Ten Years, Fair Value	8,225
Other mortgage-related securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	3,524	[1]	3,687	[1]
Available-for-sale, at fair value	3,256		3,458
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	11
After Ten Years, Amortized Cost	3,524
After Ten Years, Fair Value	$ 3,245

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

[2] Amortized cost includes $610 million and $686 million as of June 30, 2012 and December 31, 2011, respectively, of increase to the carrying amount from previous fair value hedge accounting.