Accounts Receivable (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Accounts Notes And Loans Receivable [Line Items]
Accounts Receivable, Net, Current	$ 327	$ 292
Allowance for Doubtful Accounts Receivable, Current	(16)	(16)
Revenue
Accounts Notes And Loans Receivable [Line Items]
Accounts Receivable, Net, Current	217	175
Joint interest
Accounts Notes And Loans Receivable [Line Items]
Accounts Receivable, Net, Current	104	108
Other
Accounts Notes And Loans Receivable [Line Items]
Accounts Receivable, Net, Current	$ 22	$ 25