Derivative Instruments - Location and Amounts of Pre-Tax Gains (Losses) on Cash Flow Hedges (Details) - Foreign exchange forward contracts - Designated as Hedging Instrument - Cash Flow Hedging - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Accumulated Other Comprehensive Loss (effective portion)	$ 1	$ 5
Selling and general expenses
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified from Accumulated Other Comprehensive Loss into Income (effective portion)	$ 1	$ 1