Derivative Instruments - Effect of Derivative Instruments - Statement of Income Table (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Derivative [Line Items]
Unrealized (gains) losses on derivatives, net					$ (395)		$ 83
Total (gains) losses on derivatives, net	(656)		(44)		(465)		(328)
Gathering, Processing, and Marketing Sales and Gains (Losses) on Derivatives, Net [Member]
Derivative [Line Items]
Realized (gains) losses on derivatives, net	(18)		(262)		(65)		(401)
Unrealized (gains) losses on derivatives, net	(641)		225		(395)		83
Total (gains) losses on derivatives, net	(659)		(37)		(460)		(318)
Commodity Derivatives [Member] | Gathering, Processing, and Marketing Sales [Member]
Derivative [Line Items]
Realized (gains) losses on derivatives, net	3	[1]	(1)	[1]	7	[1]	(3)	[1]
Unrealized (gains) losses on derivatives, net	(6)	[1]	8	[1]	(2)	[1]	13	[1]
Total (gains) losses on derivatives, net	(3)	[1]	7	[1]	5	[1]	10	[1]
Commodity Derivatives [Member] | (Gains) Losses on Derivatives, net [Member]
Derivative [Line Items]
Realized (gains) losses on derivatives, net	(21)		(263)		(72)		(400)
Unrealized (gains) losses on derivatives, net	(373)		(157)		(39)		(68)
Total (gains) losses on derivatives, net	(394)		(420)		(111)		(468)
Interest-Rate and Other Derivatives [Member] | (Gains) Losses on Derivatives, net [Member]
Derivative [Line Items]
Realized (gains) losses on derivatives, net			2				2
Unrealized (gains) losses on derivatives, net	(262)		374		(354)		138
Total (gains) losses on derivatives, net	$ (262)		$ 376		$ (354)		$ 140

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