Derivative Instruments and Hedging Activities (Details 3) (USD $) In Millions	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010
Commodity Derivative Activity in Accumulated Other Comprehensive Income (Loss)
Unrealized loss on derivatives at beginning of period, before tax	$ (54)	$ (267)
Realized amounts reclassified into earnings, before tax	36	(104)
Net change in derivative fair value, before tax	304	596
Ineffectiveness reclassified into earnings, before tax	(16)
Unrealized gain on derivatives at end of period, before tax	270	225
Unrealized loss on derivatives at beginning of period, after tax	(19)	(170)
Realized amounts reclassified into earnings, after tax	32	(67)
Net change in derivative fair value, after tax	181	407
Ineffectiveness reclassified into earnings, after tax	(10)
Unrealized gain on derivatives at end of period, after tax	$ 184	$ 170