Income Taxes (Summary of Operating Loss And Tax Credit Carryforwards) (Details) $ in Millions	Dec. 31, 2017 USD ($)
Operating Loss Carryforwards [Line Items]
Operating loss and tax credit carryforwards	$ 1,202
2018 Through 2027
Operating Loss Carryforwards [Line Items]
Operating loss and tax credit carryforwards	413
2028 Through 2037
Operating Loss Carryforwards [Line Items]
Operating loss and tax credit carryforwards	88
Indefinite
Operating Loss Carryforwards [Line Items]
Operating loss and tax credit carryforwards	701
U.S. federal and non-U.S. NOLs
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	499
U.S. federal and non-U.S. NOLs | 2018 Through 2027
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	65
U.S. federal and non-U.S. NOLs | 2028 Through 2037
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	2
U.S. federal and non-U.S. NOLs | Indefinite
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	432
State taxing jurisdiction NOLs
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	215
State taxing jurisdiction NOLs | Capital Loss Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	2
State taxing jurisdiction NOLs | 2018 Through 2027
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	147
State taxing jurisdiction NOLs | 2018 Through 2027 | Capital Loss Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	2
State taxing jurisdiction NOLs | 2028 Through 2037
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	68
State taxing jurisdiction NOLs | 2028 Through 2037 | Capital Loss Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	0
State taxing jurisdiction NOLs | Indefinite
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	0
State taxing jurisdiction NOLs | Indefinite | Capital Loss Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	0
U.S. federal, non- U.S. and state tax credit carryforwards | General Business Tax Credit Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	486
U.S. federal, non- U.S. and state tax credit carryforwards | 2018 Through 2027 | General Business Tax Credit Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	199
U.S. federal, non- U.S. and state tax credit carryforwards | 2028 Through 2037 | General Business Tax Credit Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	18
U.S. federal, non- U.S. and state tax credit carryforwards | Indefinite | General Business Tax Credit Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	$ 269