Property, Plant and Equipment - Net Changes in Capitalized Exploratory Well Costs (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) Well	Dec. 31, 2019 USD ($) Well	Dec. 31, 2018 USD ($) Well
Property, Plant and Equipment [Abstract]
Beginning balance	$ 584	$ 418	$ 304
Additions to capitalized exploratory well costs pending the determination of proved reserves	111	224	128
Reclassifications to wells, facilities and equipment based on the determination of proved reserves	(111)	(58)	0
Capitalized exploratory well costs charged to expense	(125)	0	(14)
Ending balance	$ 459	$ 584	$ 418
Number of Wells at December 31 | Well	22	31	24