Exploratory Well Costs (Capitalized Exploratory Well And Project Activity) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Increase (Decrease) in Capitalized Exploratory Well Costs that are Pending Determination of Proved Reserves [Roll Forward]
Beginning capitalized exploratory well costs	$ 509	$ 505
Additions to exploratory well costs pending the determination of proved reserves	2,172	2,585
Reclassification due to determination of proved reserves	(2,011)	(2,557)
Disposition of assets	(6)	(1)
Exploratory well costs charged to exploration and abandonment expense	(4)	(23)
Ending capitalized exploratory well costs	$ 660	$ 509