Derivative Instruments - Effect of Derivative Instruments - Statement of Income Table (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Derivative [Line Items]
Total (gains) losses on derivatives, net		$ 281	$ (324)	$ 123	$ 462
Commodity Derivatives [Member] | Gathering, Processing, and Marketing Sales [Member]
Derivative [Line Items]
Total (gains) losses on derivatives, net	[1]	(1)	(1)	0	9
Commodity Derivatives [Member] | (Gains) Losses on Derivatives, Net [Member]
Derivative [Line Items]
Total (gains) losses on derivatives, net		(125)	(419)	(177)	(40)
Interest-Rate Derivatives [Member] | (Gains) Losses on Derivatives, Net [Member]
Derivative [Line Items]
Total (gains) losses on derivatives, net		$ 407	$ 96	$ 300	$ 493

[1] Represents the effect of Marketing and Trading Derivative Activities.