Property, Plant and Equipment - Net Changes in Capitalized Exploratory Well Costs (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) Well	Dec. 31, 2017 USD ($) Well	Dec. 31, 2016 USD ($) Well
Capitalized Exploratory Well Costs [Abstract]
Beginning balance	$ 304	$ 597	$ 1,415
Additions to capitalized exploratory well costs pending the determination of proved reserves	128	116	79
Reclassifications to wells, facilities and equipment based on the determination of proved reserves	0	(165)	0
Capitalized exploratory well costs charged to expense	(14)	(268)	(897)
Dispositions and other	0	24	0
Ending balance	$ 418	$ 304	$ 597
Number of Wells at December 31 | Well	24	12	17