Derivative Instruments - Effect of Derivative Instruments - Statement of Income Table (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Derivative [Line Items]
Total (gains) losses on derivatives, net		$ 299	$ 152
Commodity Derivatives [Member] | Gathering, Processing, and Marketing Sales [Member]
Derivative [Line Items]
Total (gains) losses on derivatives, net	[1]	2	0
Commodity Derivatives [Member] | (Gains) Losses on Derivatives, Net [Member]
Derivative [Line Items]
Total (gains) losses on derivatives, net		(28)	(53)
Interest-Rate Derivatives [Member] | (Gains) Losses on Derivatives, Net [Member]
Derivative [Line Items]
Total (gains) losses on derivatives, net		$ 325	$ 205

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