v2.4.0.6
Fair Value Measurements Fair Value Disclosure, Fair Value and Carrying Amounts (Details) (USD $)
In Billions, unless otherwise specified
Dec. 31, 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 $ 4.4 $ 3.5