Fair Value Measurements - Information about Assets and Liabilities Recorded at Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Assets:
Investments	$ 10	$ 11
Foreign Exchange Contracts	20	4
Total Assets at Fair Value	30	15
Liabilities:
Foreign Exchange Contracts	19	19
Total Liabilities at Fair Value	19	19
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1)
Assets:
Investments	10	11
Foreign Exchange Contracts	0	0
Total Assets at Fair Value	10	11
Liabilities:
Foreign Exchange Contracts	0	0
Total Liabilities at Fair Value	0	0
Significant Other Observable Inputs (Level 2)
Assets:
Investments	0	0
Foreign Exchange Contracts	20	4
Total Assets at Fair Value	20	4
Liabilities:
Foreign Exchange Contracts	19	19
Total Liabilities at Fair Value	19	19
Significant Unobservable Inputs (Level 3)
Assets:
Investments	0	0
Foreign Exchange Contracts	0	0
Total Assets at Fair Value	0	0
Liabilities:
Foreign Exchange Contracts	0	0
Total Liabilities at Fair Value	$ 0	$ 0