Derivative Instruments (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Ineffectiveness on Foreign Currency Fair Value Hedges is Immaterial	0
Senior Unsecured Notes 3.375% due 2024
Derivative Instruments, Gain (Loss) [Line Items]
Proceeds from Unsecured Notes Payable	$ 600
Foreign currency exchange forward contracts
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	5,871	$ 3,899
Foreign currency exchange forward contracts | Other noncurrent assets
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Asset, Fair Value, Gross Asset	1	4
Interest rate swap asset
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Asset, Fair Value, Gross Asset	0	0
Interest rate swap asset | Other noncurrent liabilities
Derivative Instruments, Gain (Loss) [Line Items]
Interest Rate Cash Flow Hedge Liability at Fair Value	44
Interest rate swap asset | Other noncurrent assets
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Asset, Fair Value, Gross Asset	5	9
Interest rate swap asset | Long-term Debt
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Asset, Fair Value, Gross Liability	5	9
Designated as Hedging Instrument | Foreign currency exchange forward contracts
Derivative Instruments, Gain (Loss) [Line Items]
Fair value of designated net investment hedges	30
Gains on derivatives designated as hedges	7	1
Notional amount	1,104	1,058
Designated as Hedging Instrument | Foreign currency exchange forward contracts | Other noncurrent assets
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Asset, Fair Value, Gross Asset	1	4
Designated as Hedging Instrument | Interest rate swap asset
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	600
Designated as Hedging Instrument | Interest rate swap asset | Fair Value Hedging
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	$ 500	$ 500