Investments in Securities Other-than-temporary Impairments 1 (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Investments, Debt and Equity Securities [Abstract]
Other-than-temporary-impairments	$ 2	$ 12	$ 31	$ 182
Subprime private-label securities [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	$ 3,299		$ 3,299
Weighted average collateral default	39.20%		39.20%
Weighted average collateral severities	54.40%		54.40%
Weighted average voluntary prepayment rates	2.60%		2.60%
Average credit enhancement	16.70%		16.70%
Alt-A Option ARM [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	$ 373		$ 373
Weighted average collateral default	25.70%		25.70%
Weighted average collateral severities	36.60%		36.60%
Weighted average voluntary prepayment rates	8.80%		8.80%
Average credit enhancement	3.90%		3.90%
Alt-A Fixed Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	$ 514		$ 514
Weighted average collateral default	13.20%		13.20%
Weighted average collateral severities	45.30%		45.30%
Weighted average voluntary prepayment rates	10.90%		10.90%
Average credit enhancement	6.80%		6.80%
Alt-A Variable Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	$ 625		$ 625
Weighted average collateral default	18.50%		18.50%
Weighted average collateral severities	30.10%		30.10%
Weighted average voluntary prepayment rates	8.70%		8.70%
Average credit enhancement	4.70%		4.70%
Alt-A Hybrid Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	$ 674		$ 674
Weighted average collateral default	7.40%		7.40%
Weighted average collateral severities	30.50%		30.50%
Weighted average voluntary prepayment rates	13.50%		13.50%
Average credit enhancement	1.80%		1.80%