Components of Natural Gas and Oil Sales (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Disclosure Components Of Natural Gas And Oil Sales [Abstract]
Natural gas, oil and NGL sales	$ 1,464	$ 1,427	$ 3,798	$ 3,892
Gains (losses) on natural gas, oil and NGL derivatives	(27)	980	824	783
Gains (losses) on ineffectiveness of cash flow hedges	0	(5)	0	13
Total natural gas, oil and NGL sales	$ 1,437	$ 2,402	$ 4,622	$ 4,688