Asset Retirement Obligations (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Carrying amount at January 1		$ 2,931	$ 2,059
Liabilities acquired	[1]	4	813
Liabilities incurred		191	93
Property dispositions		(154)	(88)
Liabilities settled		(135)	(225)
Accretion expense		144	100
Revisions in estimated liabilities		(187)	179
Carrying amount at December 31		$ 2,794	$ 2,931

[1] In December 2016, the Company closed the GOM Acquisition. See Note 3—Acquisitions, Divestitures, and Assets Held for Sale for additional information.