Investments in Securities Available-for-sale Securities 2 (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 57,917	[1]	$ 61,766	[1]
Gross unrealized gains	3,744		3,464
Gross unrealized losses - OTTI	(844)	[2]	(1,369)	[2]
Gross unrealized losses - Other	(488)	[3]	(680)	[3]
Available-for-sale, at fair value	60,329		63,181
Fannie Mae [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	8,015	[1]	9,580	[1]
Gross unrealized gains	740		871
Gross unrealized losses - OTTI	0	[2]	0	[2]
Gross unrealized losses - Other	(8)	[3]	(16)	[3]
Available-for-sale, at fair value	8,747		10,435
Freddie Mac [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	7,970	[1]	8,652	[1]
Gross unrealized gains	662		728
Gross unrealized losses - OTTI	0	[2]	0	[2]
Gross unrealized losses - Other	0	[3]	0	[3]
Available-for-sale, at fair value	8,632		9,380
Ginnie Mae [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	609	[1]	645	[1]
Gross unrealized gains	100		106
Gross unrealized losses - OTTI	0	[2]	0	[2]
Gross unrealized losses - Other	0	[3]	0	[3]
Available-for-sale, at fair value	709		751
Alt-A private-label securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	10,968	[1]	11,356	[1]
Gross unrealized gains	620		452
Gross unrealized losses - OTTI	(412)	[2]	(637)	[2]
Gross unrealized losses - Other	(50)	[3]	(96)	[3]
Available-for-sale, at fair value	11,126		11,075
Subprime private-label securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	7,882	[1]	8,137	[1]
Gross unrealized gains	477		217
Gross unrealized losses - OTTI	(356)	[2]	(669)	[2]
Gross unrealized losses - Other	(135)	[3]	(238)	[3]
Available-for-sale, at fair value	7,868		7,447
CMBS [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	11,910	[1],[4]	12,284	[1],[4]
Gross unrealized gains	883		824
Gross unrealized losses - OTTI	0	[2]	0	[2]
Gross unrealized losses - Other	(6)	[3]	(11)	[3]
Available-for-sale, at fair value	12,787		13,097
Includes increases to the carrying amount of amortized cost from previous fair value hedge accounting	475		527
Mortgage revenue bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	7,325	[1]	7,782	[1]
Gross unrealized gains	138		157
Gross unrealized losses - OTTI	(49)	[2]	(45)	[2]
Gross unrealized losses - Other	(59)	[3]	(52)	[3]
Available-for-sale, at fair value	7,355		7,842
Other mortgage-related securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	3,238	[1]	3,330	[1]
Gross unrealized gains	124		109
Gross unrealized losses - OTTI	(27)	[2]	(18)	[2]
Gross unrealized losses - Other	(230)	[3]	(267)	[3]
Available-for-sale, at fair value	$ 3,105		$ 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 $475 million and $527 million as of March 31, 2013 and December 31, 2012, respectively, of increases to the carrying amount from previous fair value hedge accounting.