Exploratory Costs (Schedule Of Capitalized Exploratory Well And Project Activity) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2017
Increase (Decrease) in Capitalized Exploratory Well Costs that are Pending Determination of Proved Reserves [Roll Forward]
Beginning capitalized exploratory well costs	$ 443	$ 323
Additions to exploratory well costs pending the determination of proved reserves	474	1,369
Reclassification due to determination of proved reserves	(482)	(1,247)
Exploratory well costs charged to exploration and abandonment expense	(1)	(11)
Ending capitalized exploratory well costs	$ 434	$ 434