Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Summary of financial instruments recognized at fair value and fair value measurement used
Cash	$ 915	$ 577
Short-term investments	794	527
Net derivative contracts	(35)	83
Long-term debt converted to floating interest rates by interest rate swaps - net	(39)	87
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	915	577
Short-term investments	794	527
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	(35)	83
Long-term debt converted to floating interest rates by interest rate swaps - net	(39)	87
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