Exploratory Costs (Schedule Of Capitalized Exploratory Well And Project Activity) (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2015 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2014
Beginning capitalized exploratory costs	$ 270	$ 305
Additions to exploratory costs pending the determination of proved reserves	321	782
Reclassification due to determination of proved reserves	(319)	(800)
Exploratory well costs charged to exploration expense	0	(15)
Ending capitalized exploratory costs	$ 272	$ 272
Number of projects with exploratory costs that have been suspended for a period greater than one year	0	0	0