Variable Interest Entities (Consolidated Variable Interest Entity Settlement Payments and Mark-to-Market Adjustments) (Details) - Derivative Instruments Not Designated and Not Qualifying as Hedging Instruments [Member] - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Consolidated Variable Interest Entity Settlement Payments And Mark To Market Adjustments [Line Items]
Gains (losses) for consolidated variable interest entities	[1]		$ 4
Credit Default Swaps [Member]
Consolidated Variable Interest Entity Settlement Payments And Mark To Market Adjustments [Line Items]
Gains (losses) for consolidated variable interest entities			4
Contingent Forwards [Member]
Consolidated Variable Interest Entity Settlement Payments And Mark To Market Adjustments [Line Items]
Gains (losses) for consolidated variable interest entities

[1] Reported in realized gain (loss) on our Consolidated Statements of Comprehensive Income (Loss).