Fair Value Measurements - Assets Measured on Recurring Basis (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Summary of financial instruments recognized at fair value and fair value measurement used
Cash	$ 543	$ 268
Short-term investments	203	177
Net derivative contracts	(3)	86
Long-term debt converted to floating interest rates by interest rate swaps - net	(58)	(94)
Quoted prices in active markets for identical assets (Level 1) [Member]
Summary of financial instruments recognized at fair value and fair value measurement used
Cash	543	268
Short-term investments	203	177
Net derivative contracts	0	0
Long-term debt converted to floating interest rates by interest rate swaps - net	0	0
Other observable inputs (Level 2) [Member]
Summary of financial instruments recognized at fair value and fair value measurement used
Cash	0	0
Short-term investments	0	0
Net derivative contracts	(3)	86
Long-term debt converted to floating interest rates by interest rate swaps - net	(58)	(94)
Unobservable inputs (Level 3) [Member]
Summary of financial instruments recognized at fair value and fair value measurement used
Cash	0	0
Short-term investments	0	0
Net derivative contracts	0	0
Long-term debt converted to floating interest rates by interest rate swaps - net	$ 0	$ 0