Fair Value of Assets and Liabilities (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Deposits held in money market mutual funds	$ 13	$ 8
Foreign exchange contracts	0	0
Total	13	8
Liabilities:
Foreign exchange contracts	0	0
Total	0	0
Significant Other Observable Inputs (Level 2)
Assets:
Deposits held in money market mutual funds	0	0
Foreign exchange contracts	5	5
Total	5	5
Liabilities:
Foreign exchange contracts	1	1
Total	1	1
Significant Unobservable Inputs (Level 3)
Assets:
Deposits held in money market mutual funds	0	0
Foreign exchange contracts	0	0
Total	0	0
Liabilities:
Foreign exchange contracts	0	0
Total	0	0
Total
Assets:
Deposits held in money market mutual funds	13	8
Foreign exchange contracts	5	5
Total	18	13
Liabilities:
Foreign exchange contracts	1	1
Total	$ 1	$ 1