SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Detail)			3 Months Ended
	Jan. 01, 2016	Dec. 31, 2015	Mar. 31, 2018 USD ($) $ / MMBTU	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Schedule Of Significant Accounting Policies [Line Items]
Asset impairments			$ 0
Asset impairment charges and unproved oil and gas leasehold impairments				$ 8,000,000
U.K. Petroleum Revenue Tax rate	0.00%	35.00%
Cost of purchased oil and gas			$ 104,000,000
Maximum percentage of production available to contract partners			40.00%
Revenue from customers			$ 1,700,000,000
Revenue from non-customer			155,000,000
Receivables from contracts with customer, net			1,200,000,000		$ 1,100,000,000
Oil and Gas Properties, Proved
Schedule Of Significant Accounting Policies [Line Items]
Asset impairments			0	0
Oil and Gas Properties, Unproved
Schedule Of Significant Accounting Policies [Line Items]
Asset impairments			$ 16,000,000	$ 15,000,000
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