Investments in Securities Maturity Information (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	$ 61,766	[1]	$ 78,845	[1]
Available-for-sale, at fair value	63,181		77,582
One Year or Less, Amortized Cost	48
One Year or Less, Fair Value	50
After One Year through Five Years, Amortized Cost	12,367
After One Year through Five Years, Fair Value	13,201
After Five Years through Ten Years, Amortized Cost	2,616
After Five Years through Ten Years, Fair Value	2,758
After Ten Years, Amortized Cost	46,735
After Ten Years, Fair Value	47,172
Weighted average yield	4.64%	[2]
One Year or Less, Weighted Average Yield	4.25%	[2]
After One Year through Five Years, Weighted Average Yield	3.87%	[2]
After Five Years through Ten Years, Weighted Average Yield	5.03%	[2]
After Ten Years, Weighted Average Yield	4.82%	[2]
Fannie Mae [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	9,580	[1]	15,486	[1]
Available-for-sale, at fair value	10,435		16,850
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year through Five Years, Amortized Cost	85
After One Year through Five Years, Fair Value	90
After Five Years through Ten Years, Amortized Cost	847
After Five Years through Ten Years, Fair Value	899
After Ten Years, Amortized Cost	8,648
After Ten Years, Fair Value	9,446
Freddie Mac [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	8,652	[1]	11,906	[1]
Available-for-sale, at fair value	9,380		12,823
One Year or Less, Amortized Cost	2
One Year or Less, Fair Value	2
After One Year through Five Years, Amortized Cost	79
After One Year through Five Years, Fair Value	83
After Five Years through Ten Years, Amortized Cost	786
After Five Years through Ten Years, Fair Value	845
After Ten Years, Amortized Cost	7,785
After Ten Years, Fair Value	8,450
Ginnie Mae [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	645	[1]	775	[1]
Available-for-sale, at fair value	751		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	7
After Five Years through Ten Years, Fair Value	8
After Ten Years, Amortized Cost	636
After Ten Years, Fair Value	741
Alt-A private-label securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	11,356	[1]	13,314	[1]
Available-for-sale, at fair value	11,075		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	0
After Five Years through Ten Years, Amortized Cost	178
After Five Years through Ten Years, Fair Value	183
After Ten Years, Amortized Cost	11,178
After Ten Years, Fair Value	10,892
Subprime private-label securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	8,137	[1]	9,556	[1]
Available-for-sale, at fair value	7,447		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	8,137
After Ten Years, Fair Value	7,447
CMBS [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	12,284	[1],[3]	13,949	[1],[3]
Available-for-sale, at fair value	13,097		14,026
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year through Five Years, Amortized Cost	11,892
After One Year through Five Years, Fair Value	12,699
After Five Years through Ten Years, Amortized Cost	149
After Five Years through Ten Years, Fair Value	164
After Ten Years, Amortized Cost	243
After Ten Years, Fair Value	234
Mortgage revenue bonds [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	7,782	[1]	10,172	[1]
Available-for-sale, at fair value	7,842		10,254
One Year or Less, Amortized Cost	46
One Year or Less, Fair Value	48
After One Year through Five Years, Amortized Cost	309
After One Year through Five Years, Fair Value	319
After Five Years through Ten Years, Amortized Cost	647
After Five Years through Ten Years, Fair Value	657
After Ten Years, Amortized Cost	6,780
After Ten Years, Fair Value	6,818
Other mortgage-related securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	3,330	[1]	3,687	[1]
Available-for-sale, at fair value	3,154		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	8
After Five Years through Ten Years, Amortized Cost	2
After Five Years through Ten Years, Fair Value	2
After Ten Years, Amortized Cost	3,328
After Ten Years, Fair Value	$ 3,144

[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 (“OTTI”) recognized in our consolidated statements of operations and comprehensive income (loss).

[2] Yields are determined by dividing interest income (including amortization and accretion of premiums, discounts and other cost basis adjustments) by amortized cost balances as of year-end. Yields on tax exempt obligations have been computed on a tax equivalent basis.

[3] Amortized cost includes $527 million and $686 million as of December 31, 2012 and 2011, respectively, of increases to the carrying amount from previous fair value hedge accounting.