Financial Instruments - Summary of Derivative Instruments Fair Value (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary Of Derivative Instruments By Hedge Designation [Abstract]
Net Derivative (Liability) Asset	$ (22,000,000)	$ 53,000,000
Other Assets [Member]
Summary Of Derivative Instruments By Hedge Designation [Abstract]
Derivative instruments - assets	3,000,000	92,000,000
Other Liabilities [Member]
Summary Of Derivative Instruments By Hedge Designation [Abstract]
Derivative instruments - liabilities	(25,000,000)	(39,000,000)
Designated as Hedging Instrument [Member] | Other Liabilities [Member]
Summary Of Derivative Instruments By Hedge Designation [Abstract]
Net Derivative (Liability) Asset	(13,000,000)	(16,000,000)
Cash Flow Hedging [Member]
Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Line Items]
Derivative, Gain (Loss) on Derivative, Net	0	0
Foreign exchange contracts - forwards [Member] | Designated as Hedging Instrument [Member]
Summary Of Derivative Instruments By Hedge Designation [Abstract]
Net Derivative (Liability) Asset	(14,000,000)	(20,000,000)
Foreign exchange contracts - forwards [Member] | Designated as Hedging Instrument [Member] | Other current assets [Member]
Summary Of Derivative Instruments By Hedge Designation [Abstract]
Derivative instruments - assets	1,000,000	6,000,000
Foreign exchange contracts - forwards [Member] | Designated as Hedging Instrument [Member] | Other Current Liabilities
Summary Of Derivative Instruments By Hedge Designation [Abstract]
Derivative instruments - liabilities	(15,000,000)	(26,000,000)
Foreign exchange contracts - forwards [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Summary Of Derivative Instruments By Hedge Designation [Abstract]
Net Derivative (Liability) Asset	(9,000,000)	69,000,000
Foreign exchange contracts - forwards [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Other current assets [Member]
Summary Of Derivative Instruments By Hedge Designation [Abstract]
Derivative instruments - assets	1,000,000	82,000,000
Foreign exchange contracts - forwards [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Other Current Liabilities
Summary Of Derivative Instruments By Hedge Designation [Abstract]
Derivative instruments - liabilities	(10,000,000)	(13,000,000)
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Other Long-term Assets
Summary Of Derivative Instruments By Hedge Designation [Abstract]
Derivative instruments - assets	1,000,000	4,000,000
Foreign Currency Gain (Loss) [Member] | Cash Flow Hedging [Member]
Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Line Items]
Derivative, Gain (Loss) on Derivative, Net	0	0
Foreign Currency Gain (Loss) [Member] | Foreign exchange contracts - forwards [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Line Items]
Derivative, Gain (Loss) on Derivative, Net	$ 44,000,000	$ (172,000,000)	$ (17,000,000)