SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Detail) - USD ($)			3 Months Ended			9 Months Ended
	Jan. 01, 2016	Dec. 31, 2015	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Jun. 30, 2016
Schedule Of Significant Accounting Policies [Line Items]
Asset impairment charges			$ 0		$ 836,000,000	$ 8,000,000	$ 1,009,000,000
U.K. Petroleum Revenue Tax rate	0.00%	35.00%
Impairment of certain GTP assets							105,000,000
Oil and gas property, fair value					163,000,000		163,000,000		$ 143,000,000
Cash and cash equivalents			1,846,000,000			1,846,000,000		$ 1,377,000,000
Restricted cash			96,000,000			96,000,000		0
Total cash, cash equivalents, and restricted cash shown in the statement of consolidated cash flows		$ 1,467,000,000	1,942,000,000		1,230,000,000	1,942,000,000	1,230,000,000	1,377,000,000
Accounting Standards Update 2016-09, Excess Tax Benefit Component
Schedule Of Significant Accounting Policies [Line Items]
Deferred tax assets								4,000,000
Paid-In Capital | Accounting Standards Update 2016-09
Schedule Of Significant Accounting Policies [Line Items]
Cumulative effect of new accounting principle								11,000,000
Accumulated Deficit | Accounting Standards Update 2016-09
Schedule Of Significant Accounting Policies [Line Items]
Cumulative effect of new accounting principle								(11,000,000)
Accumulated Deficit | Accounting Standards Update 2016-09, Excess Tax Benefit Component
Schedule Of Significant Accounting Policies [Line Items]
Cumulative effect of new accounting principle								$ 4,000,000
Gas Gathering, Transmission, and Processing (GTP) Assets
Schedule Of Significant Accounting Policies [Line Items]
Oil and gas property, fair value					175,000,000		175,000,000
Oil and Gas Properties, Proved
Schedule Of Significant Accounting Policies [Line Items]
Impairments for oil and gas properties			0		355,000,000	0	423,000,000
Oil and Gas Properties, Unproved
Schedule Of Significant Accounting Policies [Line Items]
Impairments for oil and gas properties			$ 160,000,000		114,000,000	$ 214,000,000	222,000,000
Recoverable PRT Decommissioning Asset
Schedule Of Significant Accounting Policies [Line Items]
Asset impairment charges				$ 8,000,000
Impairments for oil and gas properties					481,000,000		481,000,000
Canada | Oil and Gas Properties, Proved
Schedule Of Significant Accounting Policies [Line Items]
Impairments for oil and gas properties					$ 355,000,000
US and Canada | Oil and Gas Properties, Proved
Schedule Of Significant Accounting Policies [Line Items]
Impairments for oil and gas properties							$ 423,000,000