Supplemental Information On Oil And Gas Operations (Capitalized Costs) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Capitalized Costs Relating to Oil and Gas Producing Activities, by Geographic Area [Line Items]
Proved properties	$ 75,648	$ 78,190
Unproved properties	3,437	2,584
Total oil and gas properties	79,085	80,774
Accumulated DD&A	(70,430)	(69,497)
Net capitalized costs	8,655	11,277
United States [Member]
Capitalized Costs Relating to Oil and Gas Producing Activities, by Geographic Area [Line Items]
Proved properties	61,401	64,443
Unproved properties	2,092	1,352
Total oil and gas properties	63,493	65,795
Accumulated DD&A	(57,323)	(58,312)
Net capitalized costs	6,170	7,483
Canada [Member]
Capitalized Costs Relating to Oil and Gas Producing Activities, by Geographic Area [Line Items]
Proved properties	14,247	13,747
Unproved properties	1,345	1,232
Total oil and gas properties	15,592	14,979
Accumulated DD&A	(13,107)	(11,185)
Net capitalized costs	$ 2,485	$ 3,794