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Derivatives Instruments (Details 2) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Pre-tax gains and losses for energy commodity derivatives designated as cash flow hedges, as recognized in accumulated other comprehensive income (loss) (AOCI), revenues or costs and operating expenses        
Net gain (loss) recognized in other comprehensive income (loss) (effective portion) $ 55 $ (4) $ 46 $ (6)
Net gain (loss) reclassified from accumulated other comprehensive income (loss) into income (effective portion) $ 8 $ (4) $ 6 $ (4)