Offsetting Assets and Liabilities Offsetting Assets and Liabilities (Liabilities) (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Offsetting Liabilities [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 41	$ 95
Derivative Liability, Fair Value, Gross Liability	(43)	(95)
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	41	95
Derivative Asset, Not Subject to Master Netting Arrangement	(1)	(12)
Derivative, Collateral, Obligation to Return Cash	0	(9)
Derivative Asset	40	74
Derivative Liability, Fair Value, Amount Offset Against Collateral	(43)	(95)
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	12
Derivative, Collateral, Right to Reclaim Cash	4	13
Derivative Liability	(39)	(70)
Customer Securities for which Entity has Right to Sell or Repledge, Fair Value	3	6
Derivative assets in net liability positions [Member]
Offsetting Liabilities [Line Items]
Derivative Asset, Fair Value, Gross Asset	1	8
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	1	8
Derivative Asset, Not Subject to Master Netting Arrangement	(1)	(8)
Derivative, Collateral, Obligation to Return Cash	0	0
Derivative Asset	0	0
Derivative assets with no offsetting arrangements [Member] [Domain]
Offsetting 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
Derivative Liabilities in Net Liability Positions [Member]
Offsetting Liabilities [Line Items]
Derivative Liability, Fair Value, Gross Liability	(43)	(91)
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Derivative Liability, Fair Value, Amount Offset Against Collateral	(43)	(91)
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	8
Derivative, Collateral, Right to Reclaim Cash	4	13
Derivative Liability	(39)	(70)
Derivative liabilities in net asset positions [Member]
Offsetting Liabilities [Line Items]
Derivative Liability, Fair Value, Gross Liability	0	(4)
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
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
Securities sold under agreement to repurchase [Member]
Offsetting Liabilities [Line Items]
Derivative Liability, Fair Value, Gross Liability	(1,322)	(676)
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Derivative Liability, Fair Value, Amount Offset Against Collateral	(1,322)	(676)
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	0
Derivative, Collateral, Right to Reclaim Cash	1,322	676
Derivative Liability	0	0
Total Derivative Liabilities [Member]
Offsetting Liabilities [Line Items]
Derivative Liability, Fair Value, Gross Liability	(1,365)	(771)
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Derivative Liability, Fair Value, Amount Offset Against Collateral	(1,365)	(771)
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	12
Derivative, Collateral, Right to Reclaim Cash	1,326	689
Derivative Liability	$ (39)	$ (70)