Supplemental Information To Statements Of Cash Flows (Schedule Of Supplemental Information To Statements Of Cash Flows) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015
Net change in working capital accounts, net of assets and liabilities assumed:
Accounts receivable	$ (284)	$ (176)		$ 942
Income taxes receivable	8	130		384
Other current assets	(12)	215		(57)
Accounts payable	105	(167)		(190)
Revenues and royalties payable	257	96		(526)
Other current liabilities	(53)	(74)		(818)
Net change in working capital	21	24	[1]	(265)	[1]
Interest paid (net of capitalized interest)	481	569		497
Income taxes paid (received)	$ 78	$ (159)		$ (279)

[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.