Derivatives and Hedging - Notional and fair values of derivative instruments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Other Current Assets
Derivative [Line Items]
Derivative assets	$ 3	$ 9
Other Noncurrent Assets
Derivative [Line Items]
Derivative assets	15	23
Other Current Liabilities
Derivative [Line Items]
Derivative liabilities	5	3
Other Noncurrent Liabilities
Derivative [Line Items]
Derivative liabilities	3	3
Accounted for as hedges | Gross foreign exchange contracts
Derivative [Line Items]
Notional Amount	646	701
Derivative assets	17	31
Derivative liabilities	2	3
Not accounted for as hedges
Derivative [Line Items]
Notional Amount	915	955
Derivative assets	18	32
Derivative liabilities	8	6
Not accounted for as hedges | Gross foreign exchange contracts
Derivative [Line Items]
Notional Amount	269	254
Derivative assets	1	1
Derivative liabilities	$ 6	$ 3
Term of contract ( in days)	30 days