Investments in Securities Maturity Information (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	$ 65,425	[1]	$ 78,845	[1]
Available-for-sale, at fair value	66,352		77,582
One Year or Less, Amortized Cost	105
One Year or Less, Fair Value	109
After One Year through Five Years, Amortized Cost	12,058
After One Year through Five Years, Fair Value	12,761
After Five Years through Ten Years, Amortized Cost	3,475
After Five Years through Ten Years, Fair Value	3,676
After Ten Years, Amortized Cost	49,787
After Ten Years, Fair Value	49,806
Fannie Mae [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	10,576	[1]	15,486	[1]
Available-for-sale, at fair value	11,570		16,850
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year through Five Years, Amortized Cost	29
After One Year through Five Years, Fair Value	30
After Five Years through Ten Years, Amortized Cost	1,009
After Five Years through Ten Years, Fair Value	1,073
After Ten Years, Amortized Cost	9,538
After Ten Years, Fair Value	10,467
Freddie Mac [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	9,365	[1]	11,906	[1]
Available-for-sale, at fair value	10,190		12,823
One Year or Less, Amortized Cost	3
One Year or Less, Fair Value	3
After One Year through Five Years, Amortized Cost	58
After One Year through Five Years, Fair Value	62
After Five Years through Ten Years, Amortized Cost	876
After Five Years through Ten Years, Fair Value	945
After Ten Years, Amortized Cost	8,428
After Ten Years, Fair Value	9,180
Ginnie Mae [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	676	[1]	775	[1]
Available-for-sale, at fair value	792		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	670
After Ten Years, Fair Value	786
Alt-A private-label securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	11,768	[1]	13,314	[1]
Available-for-sale, at fair value	11,228		11,683
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	1
After Five Years through Ten Years, Amortized Cost	191
After Five Years through Ten Years, Fair Value	197
After Ten Years, Amortized Cost	11,577
After Ten Years, Fair Value	11,030
Subprime private-label securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	8,402	[1]	9,556	[1]
Available-for-sale, at fair value	7,372		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	8,402
After Ten Years, Fair Value	7,372
CMBS [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	12,609	[1],[2]	13,949	[1],[2]
Available-for-sale, at fair value	13,321		14,026
One Year or Less, Amortized Cost	44
One Year or Less, Fair Value	46
After One Year through Five Years, Amortized Cost	11,601
After One Year through Five Years, Fair Value	12,288
After Five Years through Ten Years, Amortized Cost	711
After Five Years through Ten Years, Fair Value	751
After Ten Years, Amortized Cost	253
After Ten Years, Fair Value	236
Mortgage revenue bonds [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	8,604	[1]	10,172	[1]
Available-for-sale, at fair value	8,673		10,254
One Year or Less, Amortized Cost	58
One Year or Less, Fair Value	60
After One Year through Five Years, Amortized Cost	368
After One Year through Five Years, Fair Value	378
After Five Years through Ten Years, Amortized Cost	684
After Five Years through Ten Years, Fair Value	695
After Ten Years, Amortized Cost	7,494
After Ten Years, Fair Value	7,540
Other mortgage-related securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	3,425	[1]	3,687	[1]
Available-for-sale, at fair value	3,206		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	3,425
After Ten Years, Fair Value	$ 3,195

[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 $566 million and $686 million as of September 30, 2012 and December 31, 2011, respectively, of increase to the carrying amount from previous fair value hedge accounting.