Segment Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Total operating revenues	$ 1,072	$ 592
Depreciation, depletion and amortization expense	96	113
Impairments	0	1,479
Operating income (loss)	301	(1,490)
Interest expense	31	19
(Loss) gain on derivatives	(191)	339
Gain on early extinguishment of debt	0	28
Other income, net	1	1
Benefit from income taxes	0	406
Assets	5,247	5,275	$ 5,160
Capital investments	266	237
Restructuring charges	6	10
Montage merger-related expenses	1	0
Change in accrued expenditures	38	8
Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	630	300
E&P
Segment Reporting Information [Line Items]
Total operating revenues	719	353
Depreciation, depletion and amortization expense	94	111
Impairments		1,479
Operating income (loss)	295	(1,486)
Interest expense	31	19
(Loss) gain on derivatives	(191)	339
Gain on early extinguishment of debt		0
Other income, net	1	1
Benefit from income taxes		406
Assets	4,741	4,900
Capital investments	266	237
Restructuring charges	6	10
Montage merger-related expenses	1
E&P | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	(14)	(9)
Marketing
Segment Reporting Information [Line Items]
Total operating revenues	353	239
Depreciation, depletion and amortization expense	2	2
Impairments		0
Operating income (loss)	6	(4)
Interest expense	0	0
(Loss) gain on derivatives	0	0
Gain on early extinguishment of debt		0
Other income, net	0	0
Benefit from income taxes		0
Assets	396	214
Capital investments	0	0
Marketing | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	644	309
Other
Segment Reporting Information [Line Items]
Total operating revenues	0	0
Depreciation, depletion and amortization expense	0	0
Impairments		0
Operating income (loss)	0	0
Interest expense	0	0
(Loss) gain on derivatives	0	0
Gain on early extinguishment of debt		28
Other income, net	0	0
Benefit from income taxes		0
Assets	110	161
Capital investments	0	0
Other | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	$ 0	$ 0