Offsetting Assets and Liabilities Offsetting Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 300	$ 2,298
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(93)	(1,291)
Derivative, Collateral, Right to Reclaim Cash	(109)	(841)
Derivative Liability, Fair Value, Gross Liability	(228)	(2,468)
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	92	1,291
Derivative, Collateral, Obligation to Return Cash	98	1,092
Securities Sold under Agreements to Repurchase, Gross	(566)	0
Securities Sold under Agreements to Repurchase, Amount Offset Against Collateral	0
Securities Sold under Agreements to Repurchase, Amount Offset Against Collateral, Net	(566)
Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Securities	0
Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Cash	290
Securities Sold under Agreements to Repurchase	(276)
Net Asset [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	256	1,395
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(83)	(503)
Derivative, Collateral, Right to Reclaim Cash	(109)	(841)
Derivative assets in net liability positions [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	10	788
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(10)	(788)
Derivative, Collateral, Right to Reclaim Cash	0	0
Derivative assets with no offsetting arrangements [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	34	115
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0	0
Derivative, Collateral, Right to Reclaim Cash	0	0
Net liability [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	(125)	(1,929)
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	10	788
Derivative, Collateral, Obligation to Return Cash	98	1,092
Derivative liabilities in net asset positions [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	(82)	(503)
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	82	503
Derivative, Collateral, Obligation to Return Cash	0	0
Derivative liabilities with no offsetting arrangements [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	(21)	(36)
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
Assets [Member]
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	300	2,298
Derivative Assets	98	166
Assets [Member] | Net Asset [Member]
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	256	1,395
Derivative Assets	64	51
Assets [Member] | Derivative assets in net liability positions [Member]
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	10	788
Derivative Assets	0	0
Assets [Member] | Derivative assets with no offsetting arrangements [Member]
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	34	115
Derivative Assets	34	115
Liabilities, Total [Member]
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	(228)	(2,468)
Derivative Liability	(38)	(85)
Gross Amounts of Recognized Liabilities	(794)
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0
Net Amounts of Liabilities Presented in the Condensed Consolidated Balance Sheet	(794)
Gross Amounts Not Offset Against Collateral	92
Obligation to Return Cash	388
Net Amount	(314)
Liabilities, Total [Member] | Net liability [Member]
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	(125)	(1,929)
Derivative Liability	(17)	(49)
Liabilities, Total [Member] | Derivative liabilities in net asset positions [Member]
Derivative [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	(82)	(503)
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	(21)	(36)
Derivative Liability	$ (21)	$ (36)