Offsetting Assets and Liabilities Offsetting Assets and Liabilities (Assets) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Offsetting Assets and Liabilities [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 37	$ 95
Derivative Liability, Fair Value, Gross Liability	30	95
Customer Securities for which Entity has Right to Sell or Repledge, Fair Value	2	6
Derivative assets in net asset position [Member]
Offsetting Assets and Liabilities [Line Items]
Derivative Asset, Fair Value, Gross Asset	36	87
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	36	87
Derivative Asset, Not Subject to Master Netting Arrangement	0	4
Derivative, Collateral, Obligation to Return Cash	(4)	(9)
Derivative Asset	32	74
Derivative assets in net liability positions [Member]
Offsetting Assets and Liabilities [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	8
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	8
Derivative Asset, Not Subject to Master Netting Arrangement	0	8
Derivative, Collateral, Obligation to Return Cash	0	0
Derivative Asset	0	0
Derivative assets with no offsetting arrangements [Member]
Offsetting Assets and Liabilities [Line Items]
Derivative Asset, Fair Value, Gross Asset	1
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	1
Derivative Asset, Not Subject to Master Netting Arrangement	0
Derivative, Collateral, Obligation to Return Cash	0
Derivative Asset	1
Total Derivative Assets [Member]
Offsetting Assets and Liabilities [Line Items]
Derivative Asset, Fair Value, Gross Asset	37	95
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	37	95
Derivative Asset, Not Subject to Master Netting Arrangement	0	12
Derivative, Collateral, Obligation to Return Cash	(4)	(9)
Derivative Asset	33	74
Derivative Liabilities in Net Liability Positions [Member]
Offsetting Assets and Liabilities [Line Items]
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Derivative Liability, Fair Value, Gross Liability	30	91
Derivative Liability, Fair Value, Amount Offset Against Collateral	30	91
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	8
Derivative, Collateral, Right to Reclaim Cash	0	13
Derivative Liability	30	70
Derivative liabilities in net asset positions [Member]
Offsetting Assets and Liabilities [Line Items]
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Derivative Liability, Fair Value, Gross Liability	0	4
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	4
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	4
Derivative, Collateral, Right to Reclaim Cash	0	0
Derivative Liability	0	0
Total derivative liabilities excluding repurchase agreements [Member]
Offsetting Assets and Liabilities [Line Items]
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Derivative Liability, Fair Value, Gross Liability	30	95
Derivative Liability, Fair Value, Amount Offset Against Collateral	30	95
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	12
Derivative, Collateral, Right to Reclaim Cash	0	13
Derivative Liability	30	70
Securities sold under agreement to repurchase [Member]
Offsetting Assets and Liabilities [Line Items]
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Derivative Liability, Fair Value, Gross Liability	1,171	676
Derivative Liability, Fair Value, Amount Offset Against Collateral	1,171	676
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	0
Derivative, Collateral, Right to Reclaim Cash	1,171	676
Derivative Liability	0	0
Total Derivative Liabilities [Member]
Offsetting Assets and Liabilities [Line Items]
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Derivative Liability, Fair Value, Gross Liability	1,201	771
Derivative Liability, Fair Value, Amount Offset Against Collateral	1,201	771
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	12
Derivative, Collateral, Right to Reclaim Cash	1,171	689
Derivative Liability	$ 30	$ 70