Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Total operating revenues	$ 667	$ 816	$ 1,657	$ 1,736
Depreciation, depletion and amortization expense	121	142	233	285
Operating income	22	124	235	379
Interest expense	15	32	29	71
Gain (Loss) on Derivatives	152	(36)	120	(43)
Loss on early extinguishment of debt	0	(8)	0	(8)
Other (loss) income, Net	(6)	3	(5)	2
Provision (benefit) for income taxes	15	0	(411)	0
Assets	6,545	7,042	6,545	7,042	$ 5,797
Capital investments	368	403	693	741
Restructuring charges	2	18	5	18
Cash and cash equivalents	155		155		201
Property, plant and equipment	5,099		5,099		4,656
Unamortized debt expense	22		22		$ 23
Right-of-use asset	103		103
Change in accrued expenditures	39	19	105	52
Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	330	501	823	1,114
E&P
Segment Reporting Information [Line Items]
Total operating revenues	380	527	931	1,170
Depreciation, depletion and amortization expense	118	126	228	243
Operating income	30	97	240	335
Interest expense	15	32	29	71
Gain (Loss) on Derivatives	152	(36)	120	(43)
Loss on early extinguishment of debt		0		0
Other (loss) income, Net	(5)	3	(4)	3
Provision (benefit) for income taxes	15		(411)
Assets	5,945	5,583	5,945	5,583
Capital investments	367	396	692	730
Restructuring charges	2	16	5	16
E&P | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	(9)	(7)	(18)	(13)
Midstream
Segment Reporting Information [Line Items]
Total operating revenues	287	289	726	566
Depreciation, depletion and amortization expense	3	16	5	42
Operating income	(8)	27	(5)	44
Interest expense	0	0	0	0
Gain (Loss) on Derivatives	0	0	0	0
Loss on early extinguishment of debt		0		0
Other (loss) income, Net	0	0	0	(1)
Provision (benefit) for income taxes	0		0
Assets	277	1,228	277	1,228
Capital investments	0	5	0	9
Restructuring charges		2		2
Midstream | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	339	508	841	1,127
Other
Segment Reporting Information [Line Items]
Total operating revenues	0	0	0	0
Depreciation, depletion and amortization expense	0	0	0	0
Operating income	0	0	0	0
Interest expense	0	0	0	0
Gain (Loss) on Derivatives	0	0	0	0
Loss on early extinguishment of debt		(8)		(8)
Other (loss) income, Net	(1)	0	(1)	0
Provision (benefit) for income taxes	0		0
Assets	323	231	323	231
Capital investments	1	2	1	2
Cash and cash equivalents	155	37	155	37
Income tax receivable	68	89	68	89
Property, plant and equipment	50	83	50	83
Unamortized debt expense	10	12	10	12
Non-qualified retirement plan	6	8	6	8
Other assets	3	3	3	3
Right-of-use asset	29		29
Other | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	0	0	0	0
Marketing
Segment Reporting Information [Line Items]
Total operating revenues	287	265	725	518
Marketing | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	339	463	841	1,039
Marketing | Midstream | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	$ 339	$ 463	$ 841	1,039
Non-Core Gathering Assets | Midstream
Segment Reporting Information [Line Items]
Impairments				$ 10