Offsetting Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 252	$ 362
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(105)	(108)
Derivative, Collateral, Right to Reclaim Cash	(48)	(120)
Derivative Liability, Fair Value, Gross Liability	(252)	(317)
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	105	108
Derivative, Collateral, Obligation to Return Cash	83	137
Securities Sold under Agreements to Repurchase, Gross	(759)	(1,500)
Securities Sold under Agreements to Repurchase, Amount Offset Against Collateral	0	0
Securities Sold under Agreements to Repurchase, Amount Offset Against Collateral, Net	(759)	(1,500)
Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Securities	0	0
Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Cash	759	1,500
Securities Sold under Agreements to Repurchase	0	0
Net Asset [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	180	319
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(33)	(65)
Derivative, Collateral, Right to Reclaim Cash	(48)	(120)
Derivative assets in net liability positions [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	72	43
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(72)	(43)
Derivative, Collateral, Right to Reclaim Cash	0	0
Net liability [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	(219)	(252)
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	72	43
Derivative, Collateral, Obligation to Return Cash	83	137
Derivative liabilities in net asset positions [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	(33)	(65)
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	33	65
Derivative, Collateral, Obligation to Return Cash	0	0
Assets [Member]
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	252	362
Derivative Assets	99	134
Assets [Member] | Net Asset [Member]
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	180	319
Derivative Assets	99	134
Assets [Member] | Derivative assets in net liability positions [Member]
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	72	43
Derivative Assets	0	0
Liabilities, Total [Member]
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	(252)	(317)
Derivative Liability	(64)	(72)
Gross Amounts of Recognized Liabilities	(1,011)	(1,817)
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Net Amounts of Liabilities Presented in the Condensed Consolidated Balance Sheet	(1,011)	(1,817)
Gross Amounts Not Offset Against Collateral	105	108
Obligation to Return Cash	842	1,637
Net Amount	(64)	(72)
Liabilities, Total [Member] | Net liability [Member]
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	(219)	(252)
Derivative Liability	(64)	(72)
Liabilities, Total [Member] | Derivative liabilities in net asset positions [Member]
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	(33)	(65)
Derivative Liability	$ 0	$ 0