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Fair Value Measurements Assets Fair Value Nonrecurring Basis (Details) (USD $)
In Millions, unless otherwise specified
 6 Months Ended 12 Months Ended
Jun. 30, 2012
Dec. 31, 2011
Dec. 31, 2010
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Impairment of intangible assets (Excluding goodwill) $ (15) $ (39) $ (4)
Impairment of property, plant, and equipment (19) (32) (7)
Increase (Decrease) in Asset Retirement Obligations   0 1
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member]
      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair value of intangible assets measured on a non-recurring basis that was written down during the period 62 280 29
Fair value of property, plant, and equipment impaired during the period 29 92 9
Fair Value of Asset Retirement Obligations Written Down During the Period   $ (4) $ 0