Property, Plant and Equipment - Net Changes in Capitalized Exploratory Well Costs (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) Well	Dec. 31, 2016 USD ($) Well	Dec. 31, 2015 USD ($) Well
Capitalized Exploratory Well Costs [Abstract]
Beginning balance	$ 597	$ 1,415	$ 1,416
Additions to capitalized exploratory well costs pending the determination of proved reserves	116	79	424
Reclassifications to wells, facilities and equipment based on the determination of proved reserves	(165)	0	(72)
Capitalized exploratory well costs charged to expense	(268)	(897)	(356)
Dispositions and other	24	0	3
Ending balance	$ 304	$ 597	$ 1,415
Number of Wells at December 31 | Well	12	17	35