Investments in Securities Available-for-sale Securities 2 (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 61,766	[1]	$ 78,845	[1]
Gross unrealized gains	3,464		3,150
Gross unrealized losses - OTTI	(1,369)	[2]	(3,250)	[2]
Gross unrealized losses, other	(680)	[3]	(1,163)	[3]
Available-for-sale, at fair value	63,181		77,582
Fannie Mae [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	9,580	[1]	15,486	[1]
Gross unrealized gains	871		1,381
Gross unrealized losses - OTTI	0	[2]	(3)	[2]
Gross unrealized losses, other	(16)	[3]	(14)	[3]
Available-for-sale, at fair value	10,435		16,850
Freddie Mac [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	8,652	[1]	11,906	[1]
Gross unrealized gains	728		917
Gross unrealized losses - OTTI	0	[2]	0	[2]
Gross unrealized losses, other	0	[3]	0	[3]
Available-for-sale, at fair value	9,380		12,823
Ginnie Mae [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	645	[1]	775	[1]
Gross unrealized gains	106		127
Gross unrealized losses - OTTI	0	[2]	0	[2]
Gross unrealized losses, other	0	[3]	0	[3]
Available-for-sale, at fair value	751		902
Alt-A private-label securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	11,356	[1]	13,314	[1]
Gross unrealized gains	452		233
Gross unrealized losses - OTTI	(637)	[2]	(1,618)	[2]
Gross unrealized losses, other	(96)	[3]	(246)	[3]
Available-for-sale, at fair value	11,075		11,683
Subprime private-label securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	8,137	[1]	9,556	[1]
Gross unrealized gains	217		17
Gross unrealized losses - OTTI	(669)	[2]	(1,534)	[2]
Gross unrealized losses, other	(238)	[3]	(453)	[3]
Available-for-sale, at fair value	7,447		7,586
CMBS [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	12,284	[1],[4]	13,949	[1],[4]
Gross unrealized gains	824		181
Gross unrealized losses - OTTI	0	[2]	0	[2]
Gross unrealized losses, other	(11)	[3]	(104)	[3]
Available-for-sale, at fair value	13,097		14,026
Deferred (gain) loss on discontinuation of fair value hedge	527		686
Mortgage revenue bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	7,782	[1]	10,172	[1]
Gross unrealized gains	157		202
Gross unrealized losses - OTTI	(45)	[2]	(56)	[2]
Gross unrealized losses, other	(52)	[3]	(64)	[3]
Available-for-sale, at fair value	7,842		10,254
Other mortgage-related securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	3,330	[1]	3,687	[1]
Gross unrealized gains	109		92
Gross unrealized losses - OTTI	(18)	[2]	(39)	[2]
Gross unrealized losses, other	(267)	[3]	(282)	[3]
Available-for-sale, at fair value	$ 3,154		$ 3,458

[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] Represents the noncredit component of other-than-temporary impairments losses recorded in “Accumulated other comprehensive income (loss)” as well as cumulative changes in fair value of securities for which we previously recognized the credit component of other-than-temporary impairments.

[3] Represents the gross unrealized losses on securities for which we have not recognized other-than-temporary impairments.

[4] 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.