CONDENSED CONSOLIDATING FINANCIAL INFORMATION - Statement of Operations (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended
	Feb. 28, 2017	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
REVENUES
Oil and gas net sales		$ 439	$ 404	$ 926	$ 733
Net derivative gains (losses)		43	(118)	116	(143)
Other revenue		34	31	64	49
Total revenues and other		516	317	1,106	639
COSTS AND OTHER
Production costs		216	188	427	372
General and administrative expenses		61	61	128	128
Depreciation, depletion and amortization		138	138	278	285
Taxes other than on income		31	42	64	81
Exploration expense		6	5	12	10
Other expenses (income), net		25	24	47	47
Total costs and other		477	458	956	923
OPERATING (LOSS) INCOME		39	(141)	150	(284)
NON-OPERATING INCOME (LOSS)
Interest and debt expense, net		(83)	(74)	(167)	(148)
Net gains on early extinguishment of debt			44	4	133
Gains on asset divestitures	$ 21		31	21	31
Other non-operating income (expense)		(3)		(3)
(LOSS) INCOME BEFORE INCOME TAXES		(47)	(140)	5	(268)
Income tax benefit					78
NET (LOSS) INCOME		(47)	(140)	5	(190)
Net income attributable to noncontrolling interest		(1)
NET (LOSS) INCOME ATTRIBUTABLE TO COMMON STOCK		(48)	(140)	5	(190)
Reportable Legal Entity | Parent
REVENUES
Other revenue		18		17
Total revenues and other		18		17
COSTS AND OTHER
General and administrative expenses		51	49	104	102
Depreciation, depletion and amortization		2	1	3	3
Other expenses (income), net		2		2
Total costs and other		55	50	109	105
OPERATING (LOSS) INCOME		(37)	(50)	(92)	(105)
NON-OPERATING INCOME (LOSS)
Interest and debt expense, net		(84)	(75)	(168)	(150)
Net gains on early extinguishment of debt			44	4	133
Other non-operating income (expense)		(3)		(3)
(LOSS) INCOME BEFORE INCOME TAXES		(124)	(81)	(259)	(122)
Income tax benefit					78
NET (LOSS) INCOME		(124)	(81)	(259)	(44)
NET (LOSS) INCOME ATTRIBUTABLE TO COMMON STOCK		(124)	(81)	(259)	(44)
Reportable Legal Entity | Combined Guarantor Subsidiaries
REVENUES
Oil and gas net sales		439	403	925	732
Net derivative gains (losses)		43	(118)	117	(143)
Other revenue		33	31	63	49
Total revenues and other		515	316	1,105	638
COSTS AND OTHER
Production costs		216	187	426	371
General and administrative expenses		10	12	24	26
Depreciation, depletion and amortization		133	137	272	282
Taxes other than on income		31	42	64	81
Exploration expense		6	5	12	10
Other expenses (income), net		44	24	65	47
Total costs and other		440	407	863	817
OPERATING (LOSS) INCOME		75	(91)	242	(179)
NON-OPERATING INCOME (LOSS)
Interest and debt expense, net		1	1	1	2
Gains on asset divestitures			31	21	31
(LOSS) INCOME BEFORE INCOME TAXES		76	(59)	264	(146)
NET (LOSS) INCOME		76	(59)	264	(146)
NET (LOSS) INCOME ATTRIBUTABLE TO COMMON STOCK		76	(59)	264	(146)
Reportable Legal Entity | Combined Non-Guarantor Subsidiaries
REVENUES
Oil and gas net sales			1	1	1
Net derivative gains (losses)				(1)
Other revenue		4		5
Total revenues and other		4	1	5	1
COSTS AND OTHER
Production costs			1	1	1
Depreciation, depletion and amortization		3		3
Other expenses (income), net				1
Total costs and other		3	$ 1	5	$ 1
OPERATING (LOSS) INCOME		1
NON-OPERATING INCOME (LOSS)
(LOSS) INCOME BEFORE INCOME TAXES		1
NET (LOSS) INCOME		1
Net income attributable to noncontrolling interest		(1)
Eliminations
REVENUES
Other revenue		(21)		(21)
Total revenues and other		(21)		(21)
COSTS AND OTHER
Other expenses (income), net		(21)		(21)
Total costs and other		$ (21)		$ (21)