Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2010
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Cash	$ 425	$ 385	$ 278	$ 333
Short-term investments	620	699
Summary of financial instruments recognized at fair value and fair value measurement used
Net derivative contracts	93	46
Long-term debt converted to floating interest rates by interest rate swaps - net	92	66
Carrying value of long-term debt and current portion of long-term debt	3,997	3,687
Fair value of long-term debt and current portion of long-term debt	4,576	4,273
Quoted prices in active markets for identical assets (Level 1) [Member]
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Cash		385
Short-term investments		699
Summary of financial instruments recognized at fair value and fair value measurement used
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]
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Cash	0	0
Short-term investments	0	0
Summary of financial instruments recognized at fair value and fair value measurement used
Net derivative contracts	93	46
Long-term debt converted to floating interest rates by interest rate swaps - net	92	66
Unobservable inputs (Level 3) [Member]
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Cash	0	0
Short-term investments	0	0
Summary of financial instruments recognized at fair value and fair value measurement used
Net derivative contracts	0	0
Long-term debt converted to floating interest rates by interest rate swaps - net	$ 0	$ 0