Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Total operating revenues	$ 1,050	$ 410	$ 2,122	$ 1,002
Depreciation, depletion and amortization expense	100	84	196	197
Impairments	0	655	0	2,134
Operating income (loss)	293	(756)	594	(2,246)
Interest expense	30	22	61	41
Gain (loss) on derivatives	(871)	(109)	(1,062)	230
Gain on early extinguishment of debt	0	7	0	35
Other income (loss), net	(1)	0	0	1
Benefit from income taxes	0	0	0	406
Assets	5,394	4,555	5,394	4,555	$ 5,160
Capital investments	259	245	525	482
Restructuring charges	1	2	7	12
Merger-related expenses	3	0	4	0
Change in accrued expenditures	(9)		29	8
Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	637	190	1,267	490
E&P
Segment Reporting Information [Line Items]
Total operating revenues	718	223	1,437	576
Depreciation, depletion and amortization expense	97	81	191	192
Impairments		655		2,134
Operating income (loss)	286	(748)	581	(2,234)
Interest expense	30	22	61	41
Gain (loss) on derivatives	(872)	(109)	(1,063)	230
Gain on early extinguishment of debt		0		0
Other income (loss), net	(1)	(1)		0
Benefit from income taxes				406
Assets	4,870	4,185	4,870	4,185
Capital investments	259	245	525	482
Restructuring charges	1	2	7	12
Merger-related expenses	3		4
E&P | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	(14)	(12)	(28)	(21)
Marketing
Segment Reporting Information [Line Items]
Total operating revenues	332	187	685	426
Depreciation, depletion and amortization expense	3	3	5	5
Impairments		0		0
Operating income (loss)	7	(8)	13	(12)
Interest expense	0	0	0	0
Gain (loss) on derivatives	0	0	0	0
Gain on early extinguishment of debt		0		0
Other income (loss), net	0	0		0
Benefit from income taxes				0
Assets	408	208	408	208
Capital investments	0	0	0	0
Marketing | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	651	202	1,295	511
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
Operating income (loss)	0	0	0	0
Interest expense	0	0	0	0
Gain (loss) on derivatives	1	0	1	0
Gain on early extinguishment of debt		7		35
Other income (loss), net	0	1		1
Benefit from income taxes				0
Assets	116	162	116	162
Capital investments	0	0	0	0
Other | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	$ 0	$ 0	$ 0	$ 0