Derivative Instruments - Net Gains (Losses) from Changes in Fair Value (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Total gain (loss) recognized in income	$ 13	$ (8)	$ (7)
Derivative instruments not designated as hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Total gain (loss) recognized in income	9	(22)	5
Foreign exchange contracts | Foreign exchange loss | Derivative instruments not designated as hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Total gain (loss) recognized in income	1	(24)	5
Forward interest rate swaps | Interest expense, net | Derivative instruments not designated as hedges:
Derivative Instruments, Gain (Loss) [Line Items]
Total gain (loss) recognized in income	$ 8	$ 2	$ 0