Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Total operating revenues	$ 527	$ 636	$ 1,529	$ 2,293
Depreciation, depletion and amortization expense	70	125	267	352
Impairments	361	2	2,495	8
Operating (loss) income	(381)	(29)	(2,627)	206
Interest expense	22	17	63	46
(Loss) gain on derivatives	(192)	100	38	220
Gain on early extinguishment of debt	0	7	35	7
Other income, net	2	(2)	3	(7)
Provision (benefit) from income taxes	0	10	406	(401)
Assets	4,157	6,598	4,157	6,598	$ 6,717
Capital investments	223	240	705	933
Restructuring charges	0	4	12	9
Montage acquisition-related expenses	3	0	3	0
Cash and cash equivalents	95		95		5
Right-of-use asset	145		145		159
Property, plant and equipment	3,222		3,222		5,267
Unamortized debt expense	20		20		19
Accounts receivable	239		239		$ 345
Change in accrued expenditures	(7)	(53)	1	52
Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	266	304	756	1,127
E&P
Segment Reporting Information [Line Items]
Total operating revenues	308	357	884	1,288
Depreciation, depletion and amortization expense	68	123	260	345
Impairments	361	0	2,495	6
Operating (loss) income	(379)	(21)	(2,613)	219
Interest expense	22	17	63	46
(Loss) gain on derivatives	(192)	100	38	220
Gain on early extinguishment of debt		0	0	0
Other income, net	2	(4)	2	(8)
Provision (benefit) from income taxes		10	406	(401)
Assets	3,705	6,099	3,705	6,099
Capital investments	223	239	705	931
Restructuring charges		4	12	9
Montage acquisition-related expenses	3		3
E&P | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	(10)	(9)	(31)	(27)
Marketing
Segment Reporting Information [Line Items]
Total operating revenues	219	279	645	1,005
Depreciation, depletion and amortization expense	2	2	7	7
Impairments	0	2	0	2
Operating (loss) income	(2)	(8)	(14)	(13)
Interest expense	0	0	0	0
(Loss) gain on derivatives	0	0	0	0
Gain on early extinguishment of debt		0	0	0
Other income, net	0	0	0	0
Provision (benefit) from income taxes		0	0	0
Assets	240	272	240	272
Capital investments	0	0	0	0
Marketing | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	276	313	787	1,154
Other
Segment Reporting Information [Line Items]
Total operating revenues	0	0	0	0
Depreciation, depletion and amortization expense	0	0	0	0
Impairments	0	0	0	0
Operating (loss) income	0	0	0	0
Interest expense	0	0	0	0
(Loss) gain on derivatives	0	0	0	0
Gain on early extinguishment of debt		7	35	7
Other income, net	0	2	1	1
Provision (benefit) from income taxes		0	0	0
Assets	212	227	212	227
Capital investments	0	1	0	2
Cash and cash equivalents	95	29	95	29
Right-of-use asset	74	84	74	84
Property, plant and equipment	18	31	18	31
Unamortized debt expense	10	9	10	9
Prepayments	3	7	3	7
Income tax receivable		61		61
Accounts receivable	7		7
Other | Non-Qualified Supplemental Employee Retirement Plan
Segment Reporting Information [Line Items]
Non-qualified retirement plan	5	7	5	7
Other | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	$ 0	$ 0	$ 0	$ 0