Derivative Instruments - Effect of Derivative Instruments - Statement of Income Table (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Derivative [Line Items]
Total (gains) losses on derivatives, net	$ 254	$ 437	$ 569	$ 473
Commodity derivatives [Member] | Gathering, processing, and marketing sales [Member]
Derivative [Line Items]
Total (gains) losses on derivatives, net	0	1	2	2
Commodity derivatives [Member] | (Gains) losses on derivatives, net [Member]
Derivative [Line Items]
Total (gains) losses on derivatives, net	(5)	468	144	630
Interest-rate derivatives [Member] | (Gains) losses on derivatives, net [Member]
Derivative [Line Items]
Total (gains) losses on derivatives, net	200	(32)	328	(159)
WES [Member] | Interest-rate derivatives [Member] | (Gains) losses on derivatives, net [Member]
Derivative [Line Items]
Total (gains) losses on derivatives, net	$ 59	$ 0	$ 95	$ 0