Investments in Securities Available-for-sale Securities 2 (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 53,097	[1]	$ 61,766	[1]
Gross unrealized gains	3,621		3,464
Gross unrealized losses - OTTI	(628)	[2]	(1,369)	[2]
Gross unrealized losses - Other	(554)	[3]	(680)	[3]
Available-for-sale, at fair value	55,536		63,181
Fannie Mae [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	7,606	[1]	9,580	[1]
Gross unrealized gains	515		871
Gross unrealized losses - OTTI	0	[2]	0	[2]
Gross unrealized losses - Other	(26)	[3]	(16)	[3]
Available-for-sale, at fair value	8,095		10,435
Freddie Mac [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	7,322	[1]	8,652	[1]
Gross unrealized gains	556		728
Gross unrealized losses - OTTI	0	[2]	0	[2]
Gross unrealized losses - Other	0	[3]	0	[3]
Available-for-sale, at fair value	7,878		9,380
Ginnie Mae [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	577	[1]	645	[1]
Gross unrealized gains	91		106
Gross unrealized losses - OTTI	0	[2]	0	[2]
Gross unrealized losses - Other	0	[3]	0	[3]
Available-for-sale, at fair value	668		751
Alt-A private-label securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	10,284	[1]	11,356	[1]
Gross unrealized gains	1,071		452
Gross unrealized losses - OTTI	(172)	[2]	(637)	[2]
Gross unrealized losses - Other	(56)	[3]	(96)	[3]
Available-for-sale, at fair value	11,127		11,075
Subprime private-label securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	7,641	[1]	8,137	[1]
Gross unrealized gains	630		217
Gross unrealized losses - OTTI	(265)	[2]	(669)	[2]
Gross unrealized losses - Other	(144)	[3]	(238)	[3]
Available-for-sale, at fair value	7,862		7,447
CMBS [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	9,905	[1],[4]	12,284	[1],[4]
Gross unrealized gains	540	[4]	824	[4]
Gross unrealized losses - OTTI	0	[2],[4]	0	[2],[4]
Gross unrealized losses - Other	0	[3],[4]	(11)	[3],[4]
Available-for-sale, at fair value	10,445	[4]	13,097	[4]
Includes increases to the carrying amount of amortized cost from previous fair value hedge accounting	378		527
Mortgage revenue bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	6,627	[1]	7,782	[1]
Gross unrealized gains	68		157
Gross unrealized losses - OTTI	(170)	[2]	(45)	[2]
Gross unrealized losses - Other	(121)	[3]	(52)	[3]
Available-for-sale, at fair value	6,404		7,842
Other mortgage-related securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	3,135	[1]	3,330	[1]
Gross unrealized gains	150		109
Gross unrealized losses - OTTI	(21)	[2]	(18)	[2]
Gross unrealized losses - Other	(207)	[3]	(267)	[3]
Available-for-sale, at fair value	$ 3,057		$ 3,154

[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] Represents the noncredit component of other-than-temporary impairments losses recorded in “Accumulated other comprehensive income” 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 an other-than-temporary impairment.

[4] 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.