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 |