Supplemental Quarterly Financial Information (Schedule Of Quarterly Cash Flow Information under Successful Efforts Method) (Details) - USD ($) $ in Millions		3 Months Ended				12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015
Quarterly Financial Data [Line Items]
Net earnings						$ 1,078	$ (1,458)	[1]	$ (13,645)	[1]
Net cash from operating activities						2,909	1,500	[1]	4,898	[1]
Net cash from investing activities						(2,210)	(594)	[1]	(5,803)	[1]
Net cash from financing activities						9	(1,196)	[1]	1,812	[1]
Effect of exchange rate changes on cash						6	(61)	[1]	(77)	[1]
Net change in cash and cash equivalents						714	(351)	[1]	830	[1]
Cash and cash equivalents at beginning of period	[1]				$ 1,959	1,959	2,310		1,480
Cash and cash equivalents at end of period		$ 2,673				2,673	1,959	[1]	$ 2,310	[1]
As Reported Under Sucessful Efforts
Quarterly Financial Data [Line Items]
Net earnings		304	$ 212	$ 245	317
Net cash from operating activities		725	700	738	746
Net cash from investing activities		(712)	(457)	(587)	(454)
Net cash from financing activities		(115)	157	91	(124)
Effect of exchange rate changes on cash		(6)	12	8	(8)
Net change in cash and cash equivalents		(108)	412	250	160
Cash and cash equivalents at beginning of period		2,781	2,369	2,119	1,959	1,959
Cash and cash equivalents at end of period		$ 2,673	$ 2,781	$ 2,369	$ 2,119	$ 2,673	$ 1,959

[1] Prior year amounts have been recast due to change in accounting principle. See Note 2 in “Item 8. Financial Statements and Supplementary Data” of this report.