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, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental Information On Oil And Gas Operations [Abstract]
Standardized measure of discounted future net cash flows, beginning balance	$ 6,688	$ 20,474	$ 15,741
Net changes in prices and production costs	(2,128)	(20,756)	2,561
Oil, bitumen, gas and NGL sales, net of production costs	(2,163)	(2,704)	(6,865)
Changes in estimated future development costs	112	1,313	(768)
Extensions and discoveries, net of future development costs	660	1,129	4,836
Purchase of reserves	222	95	6,422
Sales of reserves in place	(560)	(79)	(2,384)
Revisions of quantity estimates	(32)	(1,451)	(746)
Previously estimated development costs incurred during the period	663	2,158	1,933
Accretion of discount	403	567	1,746
Foreign exchange and other	105	(1,254)	(107)
Net change in income taxes	228	7,196	(1,895)
Standardized measure of discounted future net cash flows, ending balance	$ 4,198	$ 6,688	$ 20,474