Supplemental Oil And Gas Disclosures (Standardized Measure Of Discounted Future Cash Flows Relating To Proved Reserves Disclosure) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Supplemental Oil And Gas Disclosures [Abstract]
Future cash inflows	$ 9,064	$ 11,887	$ 41,812
Future production costs	(5,880)	(7,376)	(16,477)
Future development costs	(485)	(792)	(5,750)
Future income tax expense			(4,743)
Future net cash flows	2,699	3,719	14,842
10% annual discount for estimated timing of cash flows	(1,034)	(1,302)	(7,299)
Standardized measure of discounted future net cash flows	$ 1,665	$ 2,417	$ 7,543	$ 3,736
Annual discount for estimated timing of cash flows percent	10.00%	10.00%	10.00%