Exploratory Well Costs (Capitalized Exploratory Well And Project Activity) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Increase (Decrease) in Capitalized Exploratory Well Costs that are Pending Determination of Proved Reserves [Roll Forward]
Beginning capitalized exploratory well costs	$ 660	$ 509
Additions to exploratory well costs pending the determination of proved reserves	1,163	2,172
Reclassification due to determination of proved reserves	(1,325)	(2,011)
Disposition of assets	0	6
Exploratory well costs charged to exploration and abandonment expense	0	(4)
Ending capitalized exploratory well costs	$ 498	$ 660