Fair Value Measurements and Derivatives - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable securities	$ 37	$ 40
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable securities	5	5
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Marketable securities	32	35
Fair Value, Measurements, Recurring [Member] | Foreign Exchange Forward [Member] | Not Designated as Hedging Instrument [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Currency contracts asset value	1	1
Currency contracts liability value	4	3
Fair Value, Measurements, Recurring [Member] | Foreign Exchange Forward [Member] | Cash Flow Hedging [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Currency contracts asset value	2	1
Currency contracts liability value	5	5
Fair Value, Measurements, Recurring [Member] | Currency Swap [Member] | Cash Flow Hedging [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Currency contracts liability value	$ 161	$ 177