Fair Value of Assets and Liabilities (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets: [Abstract]
Deposits held in money market mutual funds	$ 25	$ 90
Foreign exchange contracts	0	0
Total	25	90
Liabilities: [Abstract]
Foreign exchange contracts	0	0
Total	0	0
Significant Other Observable Inputs (Level 2)
Assets: [Abstract]
Deposits held in money market mutual funds	0	0
Foreign exchange contracts	4	1
Total	4	1
Liabilities: [Abstract]
Foreign exchange contracts	1	2
Total	1	2
Significant Unobservable Inputs (Level 3)
Assets: [Abstract]
Deposits held in money market mutual funds	0	0
Foreign exchange contracts	0	0
Total	0	0
Liabilities: [Abstract]
Foreign exchange contracts	0	0
Total	0	0
Estimate of Fair Value, Fair Value Disclosure [Member]
Assets: [Abstract]
Deposits held in money market mutual funds	25	90
Foreign exchange contracts	4	1
Total	29	91
Liabilities: [Abstract]
Foreign exchange contracts	1	2
Total	$ 1	$ 2