Fair Value Measurements and Derivatives - Fair Value of Financial Instruments (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Carrying Value		$ 1,804	$ 1,670
Fair Value		1,889	1,713
Term Facility [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Carrying Value		275
Other Indebtedness [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Carrying Value		29	120
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Market Approach Valuation Technique [Member] | Senior Notes Total [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Carrying Value		1,500	1,550
Fair Value		1,592	1,612
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Market Approach Valuation Technique [Member] | Term Facility [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Carrying Value		275
Fair Value		275
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Income Approach Valuation Technique [Member] | Other Indebtedness [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Carrying Value	[1]	29	120
Fair Value		$ 22	$ 101

[1] *The carrying value includes the unamortized portion of a fair value adjustment related to a terminated interest rate swap at both dates. The carrying value and fair value also include a financial liability associated with certain build-to-suit lease arrangements at both dates.