Accounting for Suspended Exploratory Wells - Summary of Changes and Aging of Capitalized Well Costs (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2019 USD ($) Project	Dec. 31, 2018 USD ($) Project	Dec. 31, 2017 USD ($) Project
Changes in company's suspended exploratory well costs
Beginning balance at January 1	$ 3,563	$ 3,702	$ 3,540
Additions to capitalized exploratory well costs pending the determination of proved reserves	244	207	323
Reclassifications to wells, facilities and equipment based on the determination of proved reserves	(500)	(13)	(113)
Capitalized exploratory well costs charged to expense	(125)	(333)	(39)
Other reductions	(141)	0	(9)
Ending balance at December 31	3,041	3,563	3,702
Aging of capitalized well costs and number of project
Exploratory well costs capitalized for a period of one year or less				$ 214	$ 202	$ 307
Exploratory well costs capitalized for a period greater than one year				2,827	3,361	3,395
Balance at December 31	$ 3,563	$ 3,702	$ 3,702	$ 3,041	$ 3,563	$ 3,702
Number of projects with exploratory well costs that have been capitalized for a period greater than one year (in projects) | Project				22	30	32