Condensed Consolidating Financial Information (Condensed Consolidating Statement of Operations) (Details) - USD ($) $ in Millions	3 Months Ended					6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018		Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Condensed Income Statements, Captions [Line Items]
Total operating revenues	$ 667		$ 816			$ 1,657	$ 1,736
Operating expenses	169		193			334	382
General and administrative expenses	40		59			77	114
Loss on sale of operating assets	3		0			3	0
Restructuring charges	2		18			5	18
Depreciation, depletion and amortization	121		142			233	285
Taxes, other than income taxes	17		15			36	38
Total operating costs and expense	645		692			1,422	1,357
Operating Income	22		124			235	379
Interest Expense, Net	15		32			29	71
Gain (Loss) on Derivatives	152		(36)			120	(43)
Gain (Loss) on Early Extinguishment of Debt	0		(8)			0	(8)
Other Income (Loss), Net	(6)		3			(5)	2
Equity in Earnings of Subsidiaries	0		0			0	0
Income (Loss) Before Income Taxes	153		51			321	259
Provision (benefit) for income taxes	15		0			(411)	0
Net Income	138	$ 594	51	[1]	$ 208	732	259	[1]
Participating securities - mandatory convertible preferred stock	0		0			0	2
Net Income Attributable to Common Stock	138		51			732	257
Other comprehensive income	4		0			4	0
Comprehensive income	142	$ 594	51	[1]	$ 208	736	259	[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					0
Restructuring charges	0		0			0	0
Depreciation, depletion and amortization	0		0			0	0
Taxes, other than income taxes	0		0			0	0
Total operating costs and expense	0		0			0	0
Operating Income	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
Other Income (Loss), Net	0		0			0	0
Equity in Earnings of Subsidiaries	(153)		(91)			(761)	(338)
Income (Loss) Before Income Taxes	(153)		(91)			(761)	(338)
Provision (benefit) for income taxes	0		0			0	0
Net Income	(153)		(91)			(761)	(338)
Participating securities - mandatory convertible preferred stock							0
Net Income Attributable to Common Stock							(338)
Other comprehensive income	0		0			0	0
Comprehensive income	(153)		(91)			(761)	(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					0
Restructuring charges	0		0			0	0
Depreciation, depletion and amortization	0		0			0	0
Taxes, other than income taxes	0		0			0	0
Total operating costs and expense	0		0			0	0
Operating Income	0		0			0	0
Interest Expense, Net	15		32			29	71
Gain (Loss) on Derivatives	0		0			0	0
Gain (Loss) on Early Extinguishment of Debt			(8)				(8)
Other Income (Loss), Net	0		0			0	0
Equity in Earnings of Subsidiaries	153		91			761	338
Income (Loss) Before Income Taxes	138		51			732	259
Provision (benefit) for income taxes	0		0			0	0
Net Income	138		51			732	259
Participating securities - mandatory convertible preferred stock							2
Net Income Attributable to Common Stock							257
Other comprehensive income	4		0			4	0
Comprehensive income	142		51			736	259
Guarantors
Condensed Income Statements, Captions [Line Items]
Total operating revenues	667		816			1,657	1,736
Operating expenses	169		193			334	382
General and administrative expenses	40		59			77	114
Loss on sale of operating assets	3					3
Restructuring charges	2		18			5	18
Depreciation, depletion and amortization	121		142			233	285
Taxes, other than income taxes	17		15			36	38
Total operating costs and expense	645		692			1,422	1,357
Operating Income	22		124			235	379
Interest Expense, Net	0		0			0	0
Gain (Loss) on Derivatives	152		(36)			120	(43)
Gain (Loss) on Early Extinguishment of Debt			0				0
Other Income (Loss), Net	(6)		3			(5)	2
Equity in Earnings of Subsidiaries	0		0			0	0
Income (Loss) Before Income Taxes	168		91			350	338
Provision (benefit) for income taxes	15		0			(411)	0
Net Income	153		91			761	338
Participating securities - mandatory convertible preferred stock							0
Net Income Attributable to Common Stock							338
Other comprehensive income	0		0			0	0
Comprehensive income	153		91			761	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					0
Restructuring charges	0		0			0	0
Depreciation, depletion and amortization	0		0			0	0
Taxes, other than income taxes	0		0			0	0
Total operating costs and expense	0		0			0	0
Operating Income	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
Other Income (Loss), Net	0		0			0	0
Equity in Earnings of Subsidiaries	0		0			0	0
Income (Loss) Before Income Taxes	0		0			0	0
Provision (benefit) for income taxes	0		0			0	0
Net Income	0		0			0	0
Participating securities - mandatory convertible preferred stock							0
Net Income Attributable to Common Stock							0
Other comprehensive income	0		0			0	0
Comprehensive income	0		0			0	0
Gas sales
Condensed Income Statements, Captions [Line Items]
Total operating revenues	275		407			705	947
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	275		407			705	947
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	47		44			86	79
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	47		44			86	79
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	58		75			139	140
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	58		75			139	140
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	287		265			725	518
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	287		265			725	518
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		24			0	48
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			24				48
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		1			2	4
Other | Eliminations
Condensed Income Statements, Captions [Line Items]
Total operating revenues			0			0	0
Other | Parent
Condensed Income Statements, Captions [Line Items]
Total operating revenues			0			0	0
Other | Guarantors
Condensed Income Statements, Captions [Line Items]
Total operating revenues			1			2	4
Other | Non-Guarantors
Condensed Income Statements, Captions [Line Items]
Total operating revenues			0			0	0
Marketing purchases
Condensed Income Statements, Captions [Line Items]
Marketing purchases	293		265			734	520
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	293		265			734	520
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.