Condensed Consolidating Financial Information (Condensed Consolidating Statement of Operations) (Details) - USD ($) $ in Millions	3 Months Ended							9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018		Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Condensed Income Statements, Captions [Line Items]
Total operating revenues	$ 636			$ 951				$ 2,293	$ 2,687
Operating expenses	189			206				523	588
General and administrative expenses	42			51				119	165
Loss on sale of operating assets	0			0				3	0
Restructuring charges	4			2				9	20
Depreciation, depletion and amortization	125			151				352	426
Impairments	2			161				8	171
Taxes, other than income taxes	15			26				51	64
Total operating costs and expense	665			885				2,087	2,242
Operating Income (Loss)	(29)			66				206	445
Interest Expense, Net	17			29				46	100
Gain (Loss) on Derivatives	100			(65)				220	(108)
Gain (Loss) on Early Extinguishment of Debt	7			0				7	(8)
Other Income (Loss), Net	(2)			(1)				(7)	1
Equity in Earnings of Subsidiaries	0			0				0	0
Income (Loss) Before Income Taxes	59			(29)				380	230
Provision (benefit) for income taxes	10			0				(401)	0
Net Income (Loss)	49	$ 138	$ 594	(29)	[1]	$ 51	$ 208	781	230	[1]
Participating securities – mandatory convertible preferred stock	0			0				0	1
Net Income (Loss) Attributable to Common Stock	49			(29)				781	229
Other comprehensive income	1	4		4				5	4
Comprehensive income (loss)	50	$ 142	$ 594	(25)	[1]	$ 51	$ 208	786	234	[1]
Eliminations
Condensed Income Statements, Captions [Line Items]
Total operating revenues	0			0				0	0
Operating expenses	0			0				0	0
General and administrative expenses	0			0				0	0
Loss on sale of operating assets								0
Restructuring charges	0			0				0	0
Depreciation, depletion and amortization	0			0				0	0
Impairments	0			0				0	0
Taxes, other than income taxes	0			0				0	0
Total operating costs and expense	0			0				0	0
Operating Income (Loss)	0			0				0	0
Interest Expense, Net	0			0				0	0
Gain (Loss) on Derivatives	0			0				0	0
Gain (Loss) on Early Extinguishment of Debt	0							0	0
Other Income (Loss), Net	0			0				0	0
Equity in Earnings of Subsidiaries	(58)			0				(819)	(338)
Income (Loss) Before Income Taxes	(58)			0				(819)	(338)
Provision (benefit) for income taxes	0			0				0	0
Net Income (Loss)	(58)			0				(819)	(338)
Participating securities – mandatory convertible preferred stock									0
Net Income (Loss) Attributable to Common Stock									(338)
Other comprehensive income	0			0				0	0
Comprehensive income (loss)	(58)			0				(819)	(338)
Parent
Condensed Income Statements, Captions [Line Items]
Total operating revenues	0			0				0	0
Operating expenses	0			0				0	0
General and administrative expenses	0			0				0	0
Loss on sale of operating assets								0
Restructuring charges	0			0				0	0
Depreciation, depletion and amortization	0			0				0	0
Impairments	0			0				0	0
Taxes, other than income taxes	0			0				0	0
Total operating costs and expense	0			0				0	0
Operating Income (Loss)	0			0				0	0
Interest Expense, Net	17			29				46	100
Gain (Loss) on Derivatives	0			0				0	0
Gain (Loss) on Early Extinguishment of Debt	7							7	(8)
Other Income (Loss), Net	0			0				0	0
Equity in Earnings of Subsidiaries	59			0				820	338
Income (Loss) Before Income Taxes	49			(29)				781	230
Provision (benefit) for income taxes	0			0				0	0
Net Income (Loss)	49			(29)				781	230
Participating securities – mandatory convertible preferred stock									1
Net Income (Loss) Attributable to Common Stock									229
Other comprehensive income	1			4				5	4
Comprehensive income (loss)	50			(25)				786	234
Guarantors
Condensed Income Statements, Captions [Line Items]
Total operating revenues	636			951				2,293	2,687
Operating expenses	189			206				523	588
General and administrative expenses	42			51				119	165
Loss on sale of operating assets								3
Restructuring charges	4			2				9	20
Depreciation, depletion and amortization	124			151				351	426
Impairments	2			161				8	171
Taxes, other than income taxes	15			26				51	64
Total operating costs and expense	664			885				2,086	2,242
Operating Income (Loss)	(28)			66				207	445
Interest Expense, Net	0			0				0	0
Gain (Loss) on Derivatives	100			(65)				220	(108)
Gain (Loss) on Early Extinguishment of Debt	0							0	0
Other Income (Loss), Net	(2)			(1)				(7)	1
Equity in Earnings of Subsidiaries	(1)			0				(1)	0
Income (Loss) Before Income Taxes	69			0				419	338
Provision (benefit) for income taxes	10			0				(401)	0
Net Income (Loss)	59			0				820	338
Participating securities – mandatory convertible preferred stock									0
Net Income (Loss) Attributable to Common Stock									338
Other comprehensive income	0			0				0	0
Comprehensive income (loss)	59			0				820	338
Non-Guarantors
Condensed Income Statements, Captions [Line Items]
Total operating revenues	0			0				0	0
Operating expenses	0			0				0	0
General and administrative expenses	0			0				0	0
Loss on sale of operating assets								0
Restructuring charges	0			0				0	0
Depreciation, depletion and amortization	1			0				1	0
Impairments	0			0				0	0
Taxes, other than income taxes	0			0				0	0
Total operating costs and expense	1			0				1	0
Operating Income (Loss)	(1)			0				(1)	0
Interest Expense, Net	0			0				0	0
Gain (Loss) on Derivatives	0			0				0	0
Gain (Loss) on Early Extinguishment of Debt	0							0	0
Other Income (Loss), Net	0			0				0	0
Equity in Earnings of Subsidiaries	0			0				0	0
Income (Loss) Before Income Taxes	(1)			0				(1)	0
Provision (benefit) for income taxes	0			0				0	0
Net Income (Loss)	(1)			0				(1)	0
Participating securities – mandatory convertible preferred stock									0
Net Income (Loss) Attributable to Common Stock									0
Other comprehensive income	0			0				0	0
Comprehensive income (loss)	(1)			0				(1)	0
Gas sales
Condensed Income Statements, Captions [Line Items]
Total operating revenues	238			465				943	1,412
Gas sales | Eliminations
Condensed Income Statements, Captions [Line Items]
Total operating revenues	0			0				0	0
Gas sales | Parent
Condensed Income Statements, Captions [Line Items]
Total operating revenues	0			0				0	0
Gas sales | Guarantors
Condensed Income Statements, Captions [Line Items]
Total operating revenues	238			465				943	1,412
Gas sales | Non-Guarantors
Condensed Income Statements, Captions [Line Items]
Total operating revenues	0			0				0	0
Oil sales
Condensed Income Statements, Captions [Line Items]
Total operating revenues	67			62				153	141
Oil sales | Eliminations
Condensed Income Statements, Captions [Line Items]
Total operating revenues	0			0				0	0
Oil sales | Parent
Condensed Income Statements, Captions [Line Items]
Total operating revenues	0			0				0	0
Oil sales | Guarantors
Condensed Income Statements, Captions [Line Items]
Total operating revenues	67			62				153	141
Oil sales | Non-Guarantors
Condensed Income Statements, Captions [Line Items]
Total operating revenues	0			0				0	0
NGL sales
Condensed Income Statements, Captions [Line Items]
Total operating revenues	52			112				191	252
NGL sales | Eliminations
Condensed Income Statements, Captions [Line Items]
Total operating revenues	0			0				0	0
NGL sales | Parent
Condensed Income Statements, Captions [Line Items]
Total operating revenues	0			0				0	0
NGL sales | Guarantors
Condensed Income Statements, Captions [Line Items]
Total operating revenues	52			112				191	252
NGL sales | Non-Guarantors
Condensed Income Statements, Captions [Line Items]
Total operating revenues	0			0				0	0
Marketing
Condensed Income Statements, Captions [Line Items]
Total operating revenues	279			287				1,004	805
Marketing | Eliminations
Condensed Income Statements, Captions [Line Items]
Total operating revenues	0			0				0	0
Marketing | Parent
Condensed Income Statements, Captions [Line Items]
Total operating revenues	0			0				0	0
Marketing | Guarantors
Condensed Income Statements, Captions [Line Items]
Total operating revenues	279			287				1,004	805
Marketing | Non-Guarantors
Condensed Income Statements, Captions [Line Items]
Total operating revenues	0			0				0	0
Gas gathering
Condensed Income Statements, Captions [Line Items]
Total operating revenues	0			25				0	73
Gas gathering | Eliminations
Condensed Income Statements, Captions [Line Items]
Total operating revenues				0					0
Gas gathering | Parent
Condensed Income Statements, Captions [Line Items]
Total operating revenues				0					0
Gas gathering | Guarantors
Condensed Income Statements, Captions [Line Items]
Total operating revenues				25					73
Gas gathering | Non-Guarantors
Condensed Income Statements, Captions [Line Items]
Total operating revenues				0					0
Other
Condensed Income Statements, Captions [Line Items]
Total operating revenues	0			0				2	4
Other | Eliminations
Condensed Income Statements, Captions [Line Items]
Total operating revenues								0	0
Other | Parent
Condensed Income Statements, Captions [Line Items]
Total operating revenues								0	0
Other | Guarantors
Condensed Income Statements, Captions [Line Items]
Total operating revenues								2	4
Other | Non-Guarantors
Condensed Income Statements, Captions [Line Items]
Total operating revenues								0	0
Marketing purchases
Condensed Income Statements, Captions [Line Items]
Marketing purchases	288			288				1,022	808
Marketing purchases | Eliminations
Condensed Income Statements, Captions [Line Items]
Marketing purchases	0			0				0	0
Marketing purchases | Parent
Condensed Income Statements, Captions [Line Items]
Marketing purchases	0			0				0	0
Marketing purchases | Guarantors
Condensed Income Statements, Captions [Line Items]
Marketing purchases	288			288				1,022	808
Marketing purchases | Non-Guarantors
Condensed Income Statements, Captions [Line Items]
Marketing purchases	$ 0			$ 0				$ 0	$ 0

[1] In 2018, deferred tax activity incurred in other comprehensive income was offset by a valuation allowance.