Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Summary of financial instruments recognized at fair value and fair value measurement used
Cash	$ 385	$ 333
Short-term investments	699	838
Net derivative contracts	46	69
Long-term debt converted to floating interest rates by interest rate swaps	66	42
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	385	333
Short-term investments	699	838
Net derivative contracts	0	0
Long-term debt converted to floating interest rates by interest rate swaps	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	46	69
Long-term debt converted to floating interest rates by interest rate swaps	66	42
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	$ 0	$ 0