Investments in Securities Available-for-sale Securities 2 (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	$ 21,491	$ 27,413
Gross unrealized gains	2,719	3,448
Gross unrealized losses - OTTI	(18)	(55)
Gross unrealized losses - Other	(31)	(152)
Total Available-for-Sale, at Fair Value	24,161	30,654
Fannie Mae [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	4,376	5,330
Gross unrealized gains	284	328
Gross unrealized losses - OTTI	0	0
Gross unrealized losses - Other	(22)	(19)
Total Available-for-Sale, at Fair Value	4,638	5,639
Freddie Mac [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	4,565	5,100
Gross unrealized gains	382	428
Gross unrealized losses - OTTI	0	0
Gross unrealized losses - Other	0	0
Total Available-for-Sale, at Fair Value	4,947	5,528
Ginnie Mae [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	380	416
Gross unrealized gains	55	60
Gross unrealized losses - OTTI	0	0
Gross unrealized losses - Other	0	0
Total Available-for-Sale, at Fair Value	435	476
Alt-A private-label securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	2,877	4,638
Gross unrealized gains	756	1,055
Gross unrealized losses - OTTI	(3)	(15)
Gross unrealized losses - Other	0	0
Total Available-for-Sale, at Fair Value	3,630	5,678
Subprime private-label securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	2,932	4,103
Gross unrealized gains	911	1,161
Gross unrealized losses - OTTI	(1)	(9)
Gross unrealized losses - Other	(5)	(15)
Total Available-for-Sale, at Fair Value	3,837	5,240
CMBS [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	1,301	1,341
Gross unrealized gains	43	56
Gross unrealized losses - OTTI	0	0
Gross unrealized losses - Other	0	0
Total Available-for-Sale, at Fair Value	1,344	1,397
Mortgage revenue bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	3,032	3,859
Gross unrealized gains	157	177
Gross unrealized losses - OTTI	(14)	(8)
Gross unrealized losses - Other	(4)	(5)
Total Available-for-Sale, at Fair Value	3,171	4,023
Other mortgage-related securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total amortized cost	2,028	2,626
Gross unrealized gains	131	183
Gross unrealized losses - OTTI	0	(23)
Gross unrealized losses - Other	0	(113)
Total Available-for-Sale, at Fair Value	$ 2,159	$ 2,673