Effect of Derivative Instruments - Statement of Income Table (Detail) (USD $) In Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Derivative [Line Items]
Unrealized (gains) losses on derivatives, net					$ 767		$ (66)
Commodity Contract [Member] | (Gains) Losses on Commodity Derivatives, Net [Member] | Nondesignated [Member]
Derivative [Line Items]
Realized (gains) losses on derivatives, net	(71)		(157)		(155)		(339)
Unrealized (gains) losses on derivatives, net	(159)		(43)		(162)		(713)
Derivative (Gain) Loss, net	(230)		(200)		(317)		(1,052)
Commodity Contract [Member] | Nondesignated [Member] | Gathering, Processing, and Marketing Sales [Member]
Derivative [Line Items]
Realized (gains) losses on derivatives, net	1	[1]			17	[1]	1	[1]
Unrealized (gains) losses on derivatives, net	(3)	[1]	(4)	[1]	(8)	[1]	(9)	[1]
Derivative (Gain) Loss, net	(2)	[1]	(4)	[1]	9	[1]	(8)	[1]
Interest Rate Contract and Other [Member] | (Gains) Losses on Other Derivatives, Net [Member] | Nondesignated [Member]
Derivative [Line Items]
Realized (gains) losses on derivatives, net					2
Unrealized (gains) losses on derivatives, net	854		221		937		656
Derivative (Gain) Loss, net	854		221		939		656
Nondesignated [Member]
Derivative [Line Items]
Realized (gains) losses on derivatives, net	(70)		(157)		(136)		(338)
Unrealized (gains) losses on derivatives, net	692	[2]	174	[2]	767	[2]	(66)	[2]
Derivative (Gain) Loss, net	622		17		631		(404)
Commodity Contract [Member] | (Gains) Losses on Commodity Derivatives, Net [Member]
Derivative [Line Items]
Derivative (Gain) Loss, net	(230)		(200)		(317)		(1,052)
Interest Rate Contract and Other [Member] | (Gains) Losses on Other Derivatives, Net [Member]
Derivative [Line Items]
Derivative (Gain) Loss, net	$ 854		$ 221		$ 939		$ 656

[1] Represents the effect of marketing and trading derivative activities.

[2] In the fourth quarter of 2010, the Company revised the definition of Adjusted EBITDAX to exclude the impact of unrealized (gains) losses on derivative instruments, net. The prior periods have been adjusted to reflect this change.