Derivative Instruments and Hedging Activities (Details 3) (USD $) In Millions	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010
Commodity Derivative Activity in Accumulated Other Comprehensive Income (Loss)
Unrealized gain (loss) on derivatives at beginning of period, before tax	$ (54)	$ (267)
Realized amounts reclassified into earnings	47	(51)
Net change in derivative fair value, before tax	(119)	514
Ineffectiveness and basis swaps reclassified into earnings, before tax	(1)
Unrealized gain (loss) on derivatives at end of period, before tax	(127)	196
Unrealized gain (loss) on derivatives at beginning of period, after tax	(19)	(170)
Realized amounts reclassified into earnings, after tax	36	(33)
Net change in derivative fair value, after tax	(94)	346
Ineffectiveness and basis swaps reclassified into earnings, after tax	(1)
Unrealized gain (loss) on derivatives at end of period, after tax	$ (78)	$ 143