Offsetting Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 315	$ 263
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(126)	(107)
Derivative, Collateral, Right to Reclaim Cash	(102)	(68)
Derivative Liability, Fair Value, Gross Liability	(268)	(252)
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	126	107
Derivative, Collateral, Obligation to Return Cash	68	54
Securities Sold under Agreements to Repurchase, Gross	(2,166)	(774)
Derivative non-cash collateral received are not recorded on our Condensed Consolidated Balance Sheet unless certain conditions are met.	10
Non-cash collateral received related to the reverse repurchase agreement are not recorded on our Condensed Consolidated Balance Sheet unless certain conditions are met.	50
Net Asset [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	261	216
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(72)	(60)
Derivative, Collateral, Right to Reclaim Cash	(102)	(68)
Derivative assets in net liability positions [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	54	47
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(54)	(47)
Derivative, Collateral, Right to Reclaim Cash	0	0
Reverse repurchase, securities borrowing, and similar arrangements [Member]
Derivative [Line Items]
Reverse repurchase, securities borrowing, and similar arrangements, Gross	50
Reverse repurchase, securities borrowing, and similar arrangements, Amount Offset Against Collateral	0
Reverse repurchase, securities borrowing, and similar arrangements, Amount Offset Against Collateral, Net	50
Reverse repurchase, securities borrowing, and similar arrangements, Amount Not Offset Against Collateral	0
Reverse repurchase, securities borrowing, and similar arrangements, Right to Reclaim Cash	0
Reverse repurchase, securities borrowing, and similar arrangements	50
Net liability [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	(186)	(188)
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	54	47
Derivative, Collateral, Obligation to Return Cash	68	54
Derivative liabilities in net asset positions [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	(72)	(60)
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	72	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	(10)	(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	(2,166)	(774)
Securities Sold under Agreements to Repurchase, Amount Offset Against Collateral	0	0
Securities Sold under Agreements to Repurchase, Amount Offset Against Collateral, Net	(2,166)	(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	2,166	774
Securities Sold under Agreements to Repurchase	0	0
Assets, Total [Member]
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	315	263
Derivative Assets	87	88
Gross Amounts of Recognized Assets	365
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0
Net Amounts of Assets Presented in the Condensed Consolidated Balance Sheet	365
Gross Amounts Not Offset Against Collateral	(126)
Right to Reclaim Cash	(102)
Net Amount	137
Assets, Total [Member] | Net Asset [Member]
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	261	216
Derivative Assets	87	88
Assets, Total [Member] | Derivative assets in net liability positions [Member]
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	54	47
Derivative Assets	0	0
Liabilities, Total [Member]
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	(268)	(252)
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Gross Amounts Not Offset Against Collateral	126	107
Net Amount	(74)	(91)
Derivative Liability	(74)	(91)
Gross Amounts of Recognized Liabilities	(2,434)	(1,026)
Net Amounts of Liabilities Presented in the Condensed Consolidated Balance Sheet	(2,434)	(1,026)
Obligation to Return Cash	2,234	828
Liabilities, Total [Member] | Net liability [Member]
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	(186)	(188)
Derivative Liability	(64)	(87)
Liabilities, Total [Member] | Derivative liabilities in net asset positions [Member]
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	(72)	(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	(10)	(4)
Derivative Liability	$ (10)	$ (4)