Condensed Consolidating Financial Information (Condensed Consolidating Statement of Operations) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Condensed Income Statements, Captions [Line Items]
Operating Revenues	$ 745	$ 636	$ 667	$ 990	$ 1,175	$ 951	$ 816	$ 920	$ 3,038	$ 3,862		$ 3,203
Operating expenses									720	785		671
General and administrative expenses									166	209		233
Restructuring charges									11	39		0
Depreciation, depletion and amortization									471	560		504
Impairments									16	171		0
(Gain) loss on sale of operating assets, net									2	(17)		(6)
Taxes, other than income taxes									62	89		94
Total Operating Costs and Expenses									2,768	3,065		2,472
Operating Income	64	(29)	22	213	352	66	124	255	270	797		731
Interest Expense, Net									65	124		135
Gain (Loss) on Derivatives									274	(118)		422
Gain (Loss) on Early Extinguishment of Debt									8	(17)		(70)
Other Income (Loss), Net									(7)	0		5
Equity in Earnings of Subsidiaries									0	0		0
Income (Loss) Before Income Taxes									480	538		953
Provision (benefit) for income taxes									(411)	1		(93)
Net Income (Loss)									891	537	[1]	1,046	[1]
Mandatory convertible preferred stock dividend									0	0		108
Participating securities - mandatory convertible preferred stock									0	2		123
Net Income (Loss) Attributable to Common Stock	$ 110	$ 49	$ 138	$ 594	$ 307	$ (29)	$ 51	$ 205	891	535		815
Other comprehensive loss									3	8		(5)
Comprehensive income									894	545	[1]	1,041	[1]
Eliminations
Condensed Income Statements, Captions [Line Items]
Operating Revenues									0	0		0
Operating expenses									(1)	0		0
General and administrative expenses									0	0		0
Restructuring charges									0	0
Depreciation, depletion and amortization									0	0		0
Impairments									0	0
(Gain) loss on sale of operating assets, net									0	0		0
Taxes, other than income taxes									0	0		0
Total Operating Costs and Expenses									(1)	0		0
Operating Income									1	0		0
Interest Expense, Net									0	0		0
Gain (Loss) on Derivatives									0	0		0
Gain (Loss) on Early Extinguishment of Debt									0	0		0
Other Income (Loss), Net									0			0
Equity in Earnings of Subsidiaries									(945)	(678)		(1,251)
Income (Loss) Before Income Taxes									(944)	(678)		(1,251)
Provision (benefit) for income taxes									0	0		0
Net Income (Loss)									(944)	(678)		(1,251)
Mandatory convertible preferred stock dividend												0
Participating securities - mandatory convertible preferred stock										0		0
Net Income (Loss) Attributable to Common Stock										(678)		(1,251)
Other comprehensive loss									0	0		(12)
Comprehensive income									(944)	(678)		(1,263)
Parent | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Operating Revenues									0	0		0
Operating expenses									0	0		0
General and administrative expenses									0	0		0
Restructuring charges									0	0
Depreciation, depletion and amortization									0	0		0
Impairments									0	0
(Gain) loss on sale of operating assets, net									0	0		0
Taxes, other than income taxes									0	0		0
Total Operating Costs and Expenses									0	0		0
Operating Income									0	0		0
Interest Expense, Net									65	124		135
Gain (Loss) on Derivatives									0	0		0
Gain (Loss) on Early Extinguishment of Debt									8	(17)		(70)
Other Income (Loss), Net									0			0
Equity in Earnings of Subsidiaries									947	678		1,251
Income (Loss) Before Income Taxes									890	537		1,046
Provision (benefit) for income taxes									0	0		0
Net Income (Loss)									890	537		1,046
Mandatory convertible preferred stock dividend												108
Participating securities - mandatory convertible preferred stock										2		123
Net Income (Loss) Attributable to Common Stock										535		815
Other comprehensive loss									3	8		(5)
Comprehensive income									893	545		1,041
Guarantors | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Operating Revenues									3,038	3,862		3,203
Operating expenses									720	785		671
General and administrative expenses									166	209		233
Restructuring charges									11	39
Depreciation, depletion and amortization									470	560		504
Impairments									16	171
(Gain) loss on sale of operating assets, net									2	(17)		(6)
Taxes, other than income taxes									62	89		94
Total Operating Costs and Expenses									2,767	3,065		2,472
Operating Income									271	797		731
Interest Expense, Net									0	0		0
Gain (Loss) on Derivatives									274	(118)		422
Gain (Loss) on Early Extinguishment of Debt									0	0		0
Other Income (Loss), Net									(7)			5
Equity in Earnings of Subsidiaries									(2)	0		0
Income (Loss) Before Income Taxes									536	679		1,158
Provision (benefit) for income taxes									(411)	1		(93)
Net Income (Loss)									947	678		1,251
Mandatory convertible preferred stock dividend												0
Participating securities - mandatory convertible preferred stock										0		0
Net Income (Loss) Attributable to Common Stock										678		1,251
Other comprehensive loss									0	0		6
Comprehensive income									947	678		1,257
Non-Guarantors | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Operating Revenues									0	0		0
Operating expenses									1	0		0
General and administrative expenses									0	0		0
Restructuring charges									0	0
Depreciation, depletion and amortization									1	0		0
Impairments									0	0
(Gain) loss on sale of operating assets, net									0	0		0
Taxes, other than income taxes									0	0		0
Total Operating Costs and Expenses									2	0		0
Operating Income									(2)	0		0
Interest Expense, Net									0	0		0
Gain (Loss) on Derivatives									0	0		0
Gain (Loss) on Early Extinguishment of Debt									0	0		0
Other Income (Loss), Net									0			0
Equity in Earnings of Subsidiaries									0	0		0
Income (Loss) Before Income Taxes									(2)	0		0
Provision (benefit) for income taxes									0	0		0
Net Income (Loss)									(2)	0		0
Mandatory convertible preferred stock dividend												0
Participating securities - mandatory convertible preferred stock										0		0
Net Income (Loss) Attributable to Common Stock										0		0
Other comprehensive loss									0	0		6
Comprehensive income									(2)	0		6
Gas sales
Condensed Income Statements, Captions [Line Items]
Operating Revenues									1,241	1,998		1,793
Gas sales | Eliminations
Condensed Income Statements, Captions [Line Items]
Operating Revenues									0	0		0
Gas sales | Parent | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Operating Revenues									0	0		0
Gas sales | Guarantors | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Operating Revenues									1,241	1,998		1,793
Gas sales | Non-Guarantors | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Operating Revenues									0	0		0
Oil sales
Condensed Income Statements, Captions [Line Items]
Operating Revenues									223	196		102
Oil sales | Eliminations
Condensed Income Statements, Captions [Line Items]
Operating Revenues									0	0		0
Oil sales | Parent | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Operating Revenues									0	0		0
Oil sales | Guarantors | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Operating Revenues									223	196		102
Oil sales | Non-Guarantors | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Operating Revenues									0	0		0
NGL sales
Condensed Income Statements, Captions [Line Items]
Operating Revenues									274	352		206
NGL sales | Eliminations
Condensed Income Statements, Captions [Line Items]
Operating Revenues									0	0		0
NGL sales | Parent | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Operating Revenues									0	0		0
NGL sales | Guarantors | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Operating Revenues									274	352		206
NGL sales | Non-Guarantors | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Operating Revenues									0	0		0
Marketing
Condensed Income Statements, Captions [Line Items]
Operating Revenues									1,297	1,222		972
Marketing | Eliminations
Condensed Income Statements, Captions [Line Items]
Operating Revenues									0	0		0
Marketing | Parent | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Operating Revenues									0	0		0
Marketing | Guarantors | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Operating Revenues									1,297	1,222		972
Marketing | Non-Guarantors | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Operating Revenues									0	0		0
Gas gathering
Condensed Income Statements, Captions [Line Items]
Operating Revenues									0	89		126
Gas gathering | Eliminations
Condensed Income Statements, Captions [Line Items]
Operating Revenues										0		0
Gas gathering | Parent | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Operating Revenues										0		0
Gas gathering | Guarantors | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Operating Revenues										89		126
Gas gathering | Non-Guarantors | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Operating Revenues										0		0
Other
Condensed Income Statements, Captions [Line Items]
Operating Revenues									3	5		4
Other | Eliminations
Condensed Income Statements, Captions [Line Items]
Operating Revenues									0	0		0
Other | Parent | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Operating Revenues									0	0		0
Other | Guarantors | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Operating Revenues									3	5		4
Other | Non-Guarantors | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Operating Revenues									0	0		0
Marketing purchases
Condensed Income Statements, Captions [Line Items]
Marketing purchases									1,320	1,229		976
Marketing purchases | Eliminations
Condensed Income Statements, Captions [Line Items]
Marketing purchases									0	0		0
Marketing purchases | Parent | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Marketing purchases									0	0		0
Marketing purchases | Guarantors | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Marketing purchases									1,320	1,229		976
Marketing purchases | Non-Guarantors | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Marketing purchases									$ 0	$ 0		$ 0

[1] In 2018 and 2017, deferred tax activity incurred in other comprehensive income was offset by a valuation allowance.