Acquisitions, Divestitures, and Assets Held for Sale - Property Exchange (Detail) - USD ($) $ in Millions		9 Months Ended
	Mar. 17, 2017	Sep. 30, 2017	Sep. 30, 2016
Nonmonetary Transaction [Line Items]
Cash payment to acquire a third party's interest in the DBJV system		$ 3,538	$ 2,618
Delaware Basin Joint Venture System [Member]
Nonmonetary Transaction [Line Items]
Third party nonoperated interest percentage to be acquired	50.00%
Western Gas Partners, LP [Member] | Delaware Basin Joint Venture System [Member]
Nonmonetary Transaction [Line Items]
Cash payment to acquire a third party's interest in the DBJV system	$ 155
Gain on acquisition	$ 126	$ 126
Operated interest percentage		100.00%
Western Gas Partners, LP [Member] | Marcellus Assets [Member]
Nonmonetary Transaction [Line Items]
Non operated interest percentage	33.75%