Accounting for Suspended Exploratory Wells (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2016 USD ($) Project	Dec. 31, 2015 USD ($) Project	Dec. 31, 2014 USD ($) Project
Changes in company's suspended exploratory well costs
Beginning balance at January 1	$ 3,312	$ 4,195	$ 3,245
Additions to capitalized exploratory well costs pending the determination of proved reserves	465	869	1,591
Reclassifications to wells, facilities and equipment based on the determination of proved reserves	(119)	(164)	(298)
Capitalized exploratory well costs charged to expense	(118)	(1,397)	(312)
Other reductions	0	(191)	(31)
Ending balance at December 31	3,540	3,312	4,195
Aging of capitalized well costs and number of project
Exploratory well costs capitalized for a period of one year or less				$ 445	$ 489	$ 1,522
Exploratory well costs capitalized for a period greater than one year				3,095	2,823	2,673
Balance at December 31	$ 3,312	$ 4,195	$ 3,245	$ 3,540	$ 3,312	$ 4,195
Number of projects with exploratory well costs that have been capitalized for a period greater than one year (in projects) | Project				35	39	51