Offsetting Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 299	$ 263
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(115)	(107)
Derivative, Collateral, Right to Reclaim Cash	(122)	(68)
Derivative Liability, Fair Value, Gross Liability	(176)	(252)
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	115	107
Derivative, Collateral, Obligation to Return Cash	11	54
Securities Sold under Agreements to Repurchase, Gross	(1,520)	(774)
Non-cash derivative collateral pledged to us is not recorded on our Condensed Consolidated Balance Sheet unless certain conditions are met.	8
Net Asset [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	298	216
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(114)	(60)
Derivative, Collateral, Right to Reclaim Cash	(122)	(68)
Derivative assets in net liability positions [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	1	47
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(1)	(47)
Derivative, Collateral, Right to Reclaim Cash	0	0
Net liability [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	(54)	(188)
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	1	47
Derivative, Collateral, Obligation to Return Cash	11	54
Derivative liabilities in net asset positions [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	(114)	(60)
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	114	60
Derivative, Collateral, Obligation to Return Cash	0	0
Derivative liabilities with no offsetting arrangements [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	(8)	(4)
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	0	0
Derivative, Collateral, Obligation to Return Cash	0	0
Securities sold under agreement to repurchase [Member]
Derivative [Line Items]
Securities Sold under Agreements to Repurchase, Gross	(1,520)	(774)
Securities Sold under Agreements to Repurchase, Amount Offset Against Collateral	0	0
Securities Sold under Agreements to Repurchase, Amount Offset Against Collateral, Net	(1,520)	(774)
Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Securities	0	0
Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Cash	1,520	774
Securities Sold under Agreements to Repurchase	0	0
Assets, Total [Member]
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	299	263
Derivative Assets	62	88
Assets, Total [Member] | Net Asset [Member]
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	298	216
Derivative Assets	62	88
Assets, Total [Member] | Derivative assets in net liability positions [Member]
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	1	47
Derivative Assets	0	0
Liabilities, Total [Member]
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	(176)	(252)
Derivative Liability	(50)	(91)
Gross Amounts of Recognized Liabilities	(1,696)	(1,026)
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Condensed Consolidated Balance Sheet	(1,696)	(1,026)
Gross Amounts Not Offset Against Collateral	115	107
Obligation to Return Cash	1,531	828
Net Amount	(50)	(91)
Liabilities, Total [Member] | Net liability [Member]
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	(54)	(188)
Derivative Liability	(42)	(87)
Liabilities, Total [Member] | Derivative liabilities in net asset positions [Member]
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	(114)	(60)
Derivative Liability	0	0
Liabilities, Total [Member] | Derivative liabilities with no offsetting arrangements [Member]
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	(8)	(4)
Derivative Liability	$ (8)	$ (4)