Derivative Instruments and Hedging Activities (Derivative Instruments Used in Net Investment Hedge Accounting Relationships) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Interest rate contracts | Cash flow hedging
Derivative Instruments, Gain (Loss) [Line Items]
Loss (gain) recognized in other comprehensive loss, cash flow hedge, interest rate contracts	$ (1)	$ 2	$ 22	$ 2
Foreign exchange contracts | Net investment hedging
Derivative Instruments, Gain (Loss) [Line Items]
Loss (gain) recognized in other comprehensive loss, net investment hedge, foreign exchange contracts	$ (2)	$ (6)	$ 5	$ (12)