Segment Information (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
	Apr. 26, 2018	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenues from external customers		$ 1,175	$ 951	$ 816	$ 920	$ 809	$ 737	$ 811	$ 846	$ 3,862	$ 3,203	$ 2,436
Depreciation, depletion and amortization expense										560	504	436
Impairments										171		2,321
Impairments of natural gas and oil properties												2,321
Operating income (loss)		352	$ 66	$ 124	$ 255	167	$ 110	$ 188	$ 266	797	731	(2,190)
Interest expense										124	135	88
Gain (loss) on derivatives										(118)	422	(339)
Loss on early extinguishment of debt	$ (8)									(17)	(70)	(51)
Other income (loss), net											5	(4)
Benefit for income taxes										1	(93)	(29)
Assets		5,797				7,521				5,797	7,521	7,076
Capital investments										1,248	1,293	648
Restructuring charges										39		73
Cash and cash equivalents		201				916				201	916	1,423	$ 15
Change in accrued expenditures										(53)		43
Gain on sale of assets, net										17	6
Amortization of intangible asset										9	9	9
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues from external customers										(2,408)	(2,081)	(1,546)
Exploration and Production [Member]
Segment Reporting Information [Line Items]
Revenues from external customers										2,551	2,105	1,435
Depreciation, depletion and amortization expense										514	440	371
Impairments										15
Impairments of natural gas and oil properties												2,321
Operating income (loss)										794	549	(2,399)
Interest expense										124	135	87
Gain (loss) on derivatives										(118)	421	(338)
Other income (loss), net										2	4
Benefit for income taxes										1	(93)	(29)
Assets		4,872				5,109				4,872	5,109	4,178
Capital investments										1,231	1,248	623
Restructuring and other one-time charges												81
Restructuring charges										37
Gain on sale of assets, net										(18)
Exploration and Production [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues from external customers										26	19	22
Midstream Services [Member]
Segment Reporting Information [Line Items]
Revenues from external customers										1,311	1,098	1,001
Depreciation, depletion and amortization expense										46	64	65
Impairments										155
Operating income (loss)										4	183	209
Interest expense												1
Gain (loss) on derivatives											1	(1)
Other income (loss), net										(2)	1	(2)
Assets		539				1,288				539	1,288	1,331
Capital investments										9	32	21
Restructuring charges										2		3
Gain on sale of assets, net										35
Midstream Services [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues from external customers										(2,434)	(2,100)	(1,568)
Other [Member]
Segment Reporting Information [Line Items]
Impairments										1
Operating income (loss)										(1)	(1)
Loss on early extinguishment of debt										(17)	(70)	(51)
Other income (loss), net												(2)
Assets		386				$ 1,124				386	1,124	1,567
Capital investments										8	13	4
Cash and cash equivalents		$ 201								201
Marketing [Member] | Midstream Services [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues from external customers										2,300	1,900	1,300
Workforce Reduction [Member]
Segment Reporting Information [Line Items]
Restructuring charges										23		73
Workforce Reduction [Member] | Exploration and Production [Member]
Segment Reporting Information [Line Items]
Restructuring charges										21		70
Workforce Reduction [Member] | Midstream Services [Member]
Segment Reporting Information [Line Items]
Restructuring charges										2		3
Marketing [Member]
Segment Reporting Information [Line Items]
Revenues from external customers										1,222	972	864
Marketing [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues from external customers										$ (2,275)	$ (1,895)	$ (1,327)