Supplemental Oil And Gas Disclosures (Capitalized Costs Relating To Oil And Gas Producing Activities Disclosure) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Supplemental Oil And Gas Disclosures [Abstract]
Proved properties	$ 20,548	$ 18,751
Unproved properties	2,105	3,727
Total capitalized costs	22,653	22,478
Less: Accumulated depreciation, depletion and amortization	(18,897)	(16,248)
Net capitalized costs	$ 3,756	$ 6,230