Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Total operating revenues	$ 410	$ 667	$ 1,002	$ 1,657
Depreciation, depletion and amortization expense	84	115	197	227
Impairments	655	6	2,134	6
Operating income (loss)	(756)	22	(2,246)	235
Interest expense	22	15	41	29
(Loss) gain on derivatives	(109)	152	230	120
Gain on early extinguishment of debt	7	0	35	0
Other income, net	0	(6)	1	(5)
Provision (benefit) from income taxes	0	15	406	(411)
Assets	4,555	6,545	4,555	6,545	$ 6,717
Capital investments	245	368	482	693
Restructuring charges	2	2	12	5
Cash and cash equivalents	10		10		5
Property, plant and equipment	3,426		3,426		5,267
Unamortized debt expense	16		16		19
Right-of-use asset	153		153		$ 159
Change in accrued expenditures		39	8	105
Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	190	330	490	823
E&P
Segment Reporting Information [Line Items]
Total operating revenues	223	380	576	931
Depreciation, depletion and amortization expense	81	112	192	222
Impairments	655	6	2,134	6
Operating income (loss)	(748)	30	(2,234)	240
Interest expense	22	15	41	29
(Loss) gain on derivatives	(109)	152	230	120
Gain on early extinguishment of debt	0		0
Other income, net	(1)	(5)	0	(4)
Provision (benefit) from income taxes	0	15	406	(411)
Assets	4,185	5,945	4,185	5,945
Capital investments	245	367	482	692
Restructuring charges	2	2	12	5
E&P | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	(12)	(9)	(21)	(18)
Marketing
Segment Reporting Information [Line Items]
Total operating revenues	187	287	426	726
Depreciation, depletion and amortization expense	3	3	5	5
Impairments	0	0	0	0
Operating income (loss)	(8)	(8)	(12)	(5)
Interest expense	0	0	0	0
(Loss) gain on derivatives	0	0	0	0
Gain on early extinguishment of debt	0		0
Other income, net	0	0	0	0
Provision (benefit) from income taxes	0	0	0	0
Assets	208	277	208	277
Capital investments	0	0	0	0
Marketing | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	202	339	511	841
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
(Loss) gain on derivatives	0	0	0	0
Gain on early extinguishment of debt	7		35
Other income, net	1	(1)	1	(1)
Provision (benefit) from income taxes	0	0	0	0
Assets	162	323	162	323
Capital investments	0	1	0	1
Cash and cash equivalents	10	155	10	155
Income tax receivable	31	68	31	68
Property, plant and equipment	21	50	21	50
Unamortized debt expense	10	10	10	10
Right-of-use asset	77	29	77	29
Prepayments	7		7
Other assets	1	5	1	5
Other | Non-Qualified Supplemental Employee Retirement Plan
Segment Reporting Information [Line Items]
Non-qualified retirement plan	5	6	5	6
Other | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	$ 0	$ 0	$ 0	$ 0