Fair Value Measurements, Derivative Assets & Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instrument [Member] | Other Long-term Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value	$ 124	$ 110
Foreign Currency Exchange Contracts [Member] | Derivatives Not Designated as Hedging Instrument [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value	10	16
Foreign Currency Exchange Contracts [Member] | Derivatives Not Designated as Hedging Instrument [Member] | Other Accrued Expenses [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value	$ 15	$ 12