SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Detail)			3 Months Ended		9 Months Ended
	Jan. 01, 2016	Dec. 31, 2015	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) $ / MMBTU	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Schedule Of Significant Accounting Policies [Line Items]
Asset impairments			$ 10,000,000	$ 0	$ 10,000,000	$ 8,000,000
U.K. Petroleum Revenue Tax rate	0.00%	35.00%
Cost of purchased oil and gas			92,000,000	44,000,000	$ 260,000,000	151,000,000
Maximum percentage of production available to contract partners					40.00%
Revenue from contract with customers, excluding assessed tax			1,900,000,000		$ 5,400,000,000
Revenue from contract with customers			1,976,000,000	1,389,000,000	5,645,000,000	4,247,000,000
Revenue from non-customer			198,000,000		534,000,000
Receivables from contracts with customer, net			1,300,000,000		1,300,000,000		$ 1,100,000,000
Oil and Gas Properties, Proved
Schedule Of Significant Accounting Policies [Line Items]
Asset impairments			0	0	0	0
Oil and Gas Properties, Unproved
Schedule Of Significant Accounting Policies [Line Items]
Asset impairments			49,000,000	$ 160,000,000	$ 86,000,000	$ 214,000,000
Dated Brent | Crude Oil | Minimum
Schedule Of Significant Accounting Policies [Line Items]
Oil and gas pricing formula sliding scale | $ / MMBTU					1.50
Dated Brent | Crude Oil | Maximum
Schedule Of Significant Accounting Policies [Line Items]
Oil and gas pricing formula sliding scale | $ / MMBTU					2.65
Oil and gas purchased
Schedule Of Significant Accounting Policies [Line Items]
Cost of purchased oil and gas			109,000,000		$ 308,000,000
Revenue from contract with customers			$ 124,000,000		$ 326,000,000