Exploratory Costs (Schedule Of Capitalized Exploratory Well And Project Activity) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2017
Beginning capitalized exploratory costs	$ 432	$ 323
Additions to exploratory costs pending the determination of proved reserves	489	895
Reclassification due to determination of proved reserves	(477)	(765)
Exploratory well costs charged to exploration expense	(1)	(10)
Ending capitalized exploratory costs	$ 443	$ 443