Supplemental Information On Oil And Gas Operations (Schedule Of Principal Changes In The Standardized Measure Of Discounted Future Net Cash Flows Attributable To Proved Reserves) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental Information On Oil And Gas Operations [Abstract]
Standardized measure of discounted future net cash flows, beginning balance	$ 11,337	$ 5,440	$ 7,883
Net changes in prices and production costs	(243)	5,218	(2,027)
Oil, bitumen, gas and NGL sales, net of production costs	(3,452)	(3,327)	(2,377)
Changes in estimated future development costs	(216)	789	112
Extensions and discoveries, net of future development costs	3,139	2,497	674
Purchase of reserves		2	224
Sales of reserves in place	(588)	(3)	(577)
Revisions of quantity estimates	(414)	(318)	(21)
Previously estimated development costs incurred during the period	962	559	663
Accretion of discount	960	1,034	537
Foreign exchange and other	(329)	(7)	72
Net change in income taxes	(964)	(547)	277
Standardized measure of discounted future net cash flows, ending balance	$ 10,192	$ 11,337	$ 5,440