Derivatives and Hedging - Notional and fair values of derivative instruments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Other Current Assets
Derivative [Line Items]
Derivative assets	$ 9	$ 5
Other Noncurrent Assets
Derivative [Line Items]
Derivative assets	23	9
Other Current Liabilities
Derivative [Line Items]
Derivative liabilities	3	6
Other Noncurrent Liabilities
Derivative [Line Items]
Derivative liabilities	3	7
Designated as Hedging Instrument | Gross Foreign exchange contracts
Derivative [Line Items]
Notional amount	701	758
Derivative assets	31	13
Derivative liabilities	3	12
Not Designated as Hedging Instrument
Derivative [Line Items]
Notional amount	955	947
Derivative assets	32	14
Derivative liabilities	6	13
Not Designated as Hedging Instrument | Gross Foreign exchange contracts
Derivative [Line Items]
Notional amount	254	189
Derivative assets		1
Derivative liabilities	$ 3	$ 1
Term of contract ( in days)	30 days