Exploratory Costs (Schedule Of Capitalized Exploratory Well And Project Activity) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2016
Beginning capitalized exploratory costs	$ 357	$ 306
Additions to exploratory costs pending the determination of proved reserves	328	991
Reclassification due to determination of proved reserves	(286)	(898)
Exploratory well costs charged to exploration expense	(1)	(1)
Ending capitalized exploratory costs	$ 398	$ 398