Derivatives and Hedging - Notional and fair values of derivative instruments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Derivatives, Fair Value
Notional Amount	$ 1,087	$ 955
Derivative Assets	46	32
Derivative Liabilities	$ 2	6
Term of derivative contract	30 days
Other Current Assets
Derivatives, Fair Value
Derivative Assets	$ 13	9
Other Noncurrent Assets
Derivatives, Fair Value
Derivative Assets	33	23
Other Current Liabilities
Derivatives, Fair Value
Derivative Liabilities	1	3
Other Noncurrent Liabilities
Derivatives, Fair Value
Derivative Liabilities	1	3
Derivatives accounted for as hedges | Gross foreign exchange contracts
Derivatives, Fair Value
Notional Amount	758	701
Derivative Assets	45	31
Derivative Liabilities	1	3
Not Designated as Hedging Instrument | Gross foreign exchange contracts
Derivatives, Fair Value
Notional Amount	329	254
Derivative Assets	1	1
Derivative Liabilities	$ 1	$ 3