Accounts Receivable And Accrued Revenues (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Trade Receivable and Accrued Revenues	$ 721	$ 640
Prepaids	21	18
Deposits and Other	37	11
Accounts Receivable and Accrued Revenues Gross	779	669
Allowance for Doubtful Accounts	(5)	(6)
Accounts Receivable and Accrued Revenues	774	663
Oil and natural gas receivable [Member]
Trade Receivable and Accrued Revenues	425	394
Midstream and marketing receivable [Member]
Trade Receivable and Accrued Revenues	284	161
Derivative financial instruments receivable [Member]
Trade Receivable and Accrued Revenues	3	4
Corporate and other receivable [Member]
Trade Receivable and Accrued Revenues	$ 9	$ 81