Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Total operating revenues	$ 1,598	$ 527	$ 3,720	$ 1,529
Depreciation, depletion and amortization expense	138	70	334	267
Impairments	6	361	6	2,495
Operating income (loss)	636	(381)	1,230	(2,627)
Interest expense	34	22	95	63
Total gain (loss) on derivatives	(2,399)	(192)	(3,461)	38
Gain (loss) on extinguishment of debt	(59)	0	(59)	35
Other income (loss), net	(1)	2	(1)	3
Benefit from income taxes	0	0	0	406
Assets	9,241	4,157	9,241	4,157	$ 5,160
Capital investments	291	223	816	705
Restructuring charges	0	0	7	12
Merger-related expenses	35	3	39	3
Increase (decrease) in accrued expenditures	34	(7)	63	1
Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	933	266	2,200	756
E&P
Segment Reporting Information [Line Items]
Total operating revenues	1,179	308	2,616	884
Depreciation, depletion and amortization expense	136	68	327	260
Impairments	6	361	6	2,495
Operating income (loss)	628	(379)	1,209	(2,613)
Interest expense	34	22	95	63
Total gain (loss) on derivatives	(2,398)	(192)	(3,461)	38
Gain (loss) on extinguishment of debt	0		0	0
Other income (loss), net	(1)	2	(1)	2
Benefit from income taxes				406
Assets	8,572	3,705	8,572	3,705
Capital investments	291	223	816	705
Restructuring charges			7	12
Merger-related expenses	35	3	39	3
E&P | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	(14)	(10)	(42)	(31)
Marketing
Segment Reporting Information [Line Items]
Total operating revenues	419	219	1,104	645
Depreciation, depletion and amortization expense	2	2	7	7
Impairments	0	0	0	0
Operating income (loss)	8	(2)	21	(14)
Interest expense	0	0	0	0
Total gain (loss) on derivatives	0	0	0	0
Gain (loss) on extinguishment of debt	0		0	0
Other income (loss), net	0	0	0	0
Benefit from income taxes				0
Assets	546	240	546	240
Capital investments	0	0	0	0
Marketing | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	947	276	2,242	787
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 income (loss)	0	0	0	0
Interest expense	0	0	0	0
Total gain (loss) on derivatives	(1)	0	0	0
Gain (loss) on extinguishment of debt	(59)		(59)	35
Other income (loss), net	0	0	0	1
Benefit from income taxes				0
Assets	123	212	123	212
Capital investments	0	0	0	0
Other | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	$ 0	$ 0	$ 0	$ 0