Derivative Instruments - Effect of Derivative Instruments - Statement of Income Table (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Derivative [Line Items]
Unrealized (gains) losses on derivatives, net					$ (359)		$ 539
Total (gains) losses on derivatives, net	72		251		(393)		(77)
Gathering, Processing, and Marketing Sales and Gains (Losses) on Derivatives, Net [Member]
Derivative [Line Items]
Realized (gains) losses on derivatives, net	28		(197)		(37)		(598)
Unrealized (gains) losses on derivatives, net	36		456		(359)		539
Total (gains) losses on derivatives, net	64		259		(396)		(59)
Commodity Derivatives [Member] | Gathering, Processing, and Marketing Sales [Member]
Derivative [Line Items]
Realized (gains) losses on derivatives, net	2	[1]	3	[1]	9	[1]	0	[1]
Unrealized (gains) losses on derivatives, net	(10)	[1]	5	[1]	(12)	[1]	18	[1]
Total (gains) losses on derivatives, net	(8)	[1]	8	[1]	(3)	[1]	18	[1]
Commodity Derivatives [Member] | (Gains) Losses on Derivatives, net [Member]
Derivative [Line Items]
Realized (gains) losses on derivatives, net	26		(200)		(46)		(600)
Unrealized (gains) losses on derivatives, net	120		437		81		369
Total (gains) losses on derivatives, net	146		237		35		(231)
Interest-Rate and Other Derivatives [Member] | (Gains) Losses on Derivatives, net [Member]
Derivative [Line Items]
Realized (gains) losses on derivatives, net	0		0		0		2
Unrealized (gains) losses on derivatives, net	(74)		14		(428)		152
Total (gains) losses on derivatives, net	$ (74)		$ 14		$ (428)		$ 154

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