Accounts Receivable (Schedule Of Components Of Accounts Receivable) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Joint interest billings	$ 165	$ 134
Other	32	29
Gross accounts receivable	1,151	1,000
Allowance for doubtful accounts	(10)	(11)
Net accounts receivable	1,141	989
Oil, Gas and NGL Sales [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	597	559
Marketing Revenues [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	$ 357	$ 278