Fair Value Measurements Fair Value Disclosure, Fair Value and Carrying Amounts (Details) (USD $) In Billions	Sep. 30, 2011	Dec. 31, 2010
Carrying value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Long-term Debt, Fair Value Disclosure	$ 4.5	$ 3.5
Estimated fair value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Long-term Debt, Fair Value Disclosure	$ 4.2	$ 3.5