Offsetting Assets and Liabilities Offsetting Assets and Liabilities (Liabilities) (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Offsetting Liabilities [Line Items]
Derivative Liability, Fair Value, Gross Liability	$ (81)	$ (95)
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Derivative Liability, Fair Value, Amount Offset Against Collateral	(81)	(95)
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	7	12
Derivative, Collateral, Right to Reclaim Cash	14	13
Derivative Liability	(60)	(70)
Customer Securities for which Entity has Right to Sell or Repledge, Fair Value	6	6
Derivative Liabilities in Net Liability Positions [Member]
Offsetting Liabilities [Line Items]
Derivative Liability, Fair Value, Gross Liability	(76)	(91)
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Derivative Liability, Fair Value, Amount Offset Against Collateral	(76)	(91)
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	2	8
Derivative, Collateral, Right to Reclaim Cash	14	13
Derivative Liability	(60)	(70)
Derivative liabilities in net asset positions [Member]
Offsetting Liabilities [Line Items]
Derivative Liability, Fair Value, Gross Liability	(5)	(4)
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Derivative Liability, Fair Value, Amount Offset Against Collateral	(5)	(4)
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	5	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	(1,146)	(676)
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Derivative Liability, Fair Value, Amount Offset Against Collateral	(1,146)	(676)
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	0	0
Derivative, Collateral, Right to Reclaim Cash	1,146	676
Derivative Liability	0	0
Total Derivative Liabilities [Member]
Offsetting Liabilities [Line Items]
Derivative Liability, Fair Value, Gross Liability	(1,227)	(771)
Gross Amounts Offset in the Condensed Consolidated Balance Sheet	0	0
Derivative Liability, Fair Value, Amount Offset Against Collateral	(1,227)	(771)
Derivative Liability, Not Subject to Master Netting Arrangement Deduction	7	12
Derivative, Collateral, Right to Reclaim Cash	1,160	689
Derivative Liability	$ (60)	$ (70)