Investments in Securities Maturity Information (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	$ 53,097	[1]	$ 61,766	[1]
Available-for-sale, at fair value	55,536		63,181
One Year or Less, Amortized Cost	34
One Year or Less, Fair Value	35
After One Year through Five Years, Amortized Cost	10,432
After One Year through Five Years, Fair Value	11,001
After Five Years through Ten Years, Amortized Cost	2,132
After Five Years through Ten Years, Fair Value	2,235
After Ten Years, Amortized Cost	40,499
After Ten Years, Fair Value	42,265
Fannie Mae [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	7,606	[1]	9,580	[1]
Available-for-sale, at fair value	8,095		10,435
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year through Five Years, Amortized Cost	256
After One Year through Five Years, Fair Value	271
After Five Years through Ten Years, Amortized Cost	531
After Five Years through Ten Years, Fair Value	567
After Ten Years, Amortized Cost	6,819
After Ten Years, Fair Value	7,257
Freddie Mac [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	7,322	[1]	8,652	[1]
Available-for-sale, at fair value	7,878		9,380
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year through Five Years, Amortized Cost	93
After One Year through Five Years, Fair Value	98
After Five Years through Ten Years, Amortized Cost	827
After Five Years through Ten Years, Fair Value	884
After Ten Years, Amortized Cost	6,402
After Ten Years, Fair Value	6,896
Ginnie Mae [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	577	[1]	645	[1]
Available-for-sale, at fair value	668		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	13
After Five Years through Ten Years, Fair Value	15
After Ten Years, Amortized Cost	563
After Ten Years, Fair Value	652
Alt-A private-label securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	10,284	[1]	11,356	[1]
Available-for-sale, at fair value	11,127		11,075
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year through Five Years, Amortized Cost	28
After One Year through Five Years, Fair Value	28
After Five Years through Ten Years, Amortized Cost	125
After Five Years through Ten Years, Fair Value	127
After Ten Years, Amortized Cost	10,131
After Ten Years, Fair Value	10,972
Subprime private-label securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	7,641	[1]	8,137	[1]
Available-for-sale, at fair value	7,862		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	7,641
After Ten Years, Fair Value	7,862
CMBS [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	9,905	[1],[2]	12,284	[1],[2]
Available-for-sale, at fair value	10,445	[2]	13,097	[2]
One Year or Less, Amortized Cost	0
One Year or Less, Fair Value	0
After One Year through Five Years, Amortized Cost	9,792
After One Year through Five Years, Fair Value	10,330
After Five Years through Ten Years, Amortized Cost	0
After Five Years through Ten Years, Fair Value	0
After Ten Years, Amortized Cost	113
After Ten Years, Fair Value	115
Mortgage revenue bonds [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	6,627	[1]	7,782	[1]
Available-for-sale, at fair value	6,404		7,842
One Year or Less, Amortized Cost	34
One Year or Less, Fair Value	35
After One Year through Five Years, Amortized Cost	262
After One Year through Five Years, Fair Value	268
After Five Years through Ten Years, Amortized Cost	595
After Five Years through Ten Years, Fair Value	598
After Ten Years, Amortized Cost	5,736
After Ten Years, Fair Value	5,503
Other mortgage-related securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost	3,135	[1]	3,330	[1]
Available-for-sale, at fair value	3,057		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	41
After Five Years through Ten Years, Fair Value	44
After Ten Years, Amortized Cost	3,094
After Ten Years, Fair Value	$ 3,008

[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 condensed consolidated statements of operations and comprehensive income.

[2] Amortized cost includes $378 million and $527 million as of June 30, 2013 and December 31, 2012, respectively, of increases to the carrying amount from previous fair value hedge accounting.