Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Total operating revenues	$ 636	$ 951	$ 2,293	$ 2,687
Depreciation, depletion and amortization expense	125	151	352	426
Impairments	2	161	8	171
Operating Income (Loss)	(29)	66	206	445
Interest expense	17	29	46	100
Gain (Loss) on Derivatives	100	(65)	220	(108)
Gain (Loss) on early extinguishment of debt	7	0	7	(8)
Other (loss) income, Net	(2)	(1)	(7)	1
Provision (benefit) for income taxes	10	0	(401)	0
Assets	6,598	7,058	6,598	7,058	$ 5,797
Capital investments	240	298	933	1,039
Restructuring charges	4	2	9	20
Cash and cash equivalents	29		29		201
Property, plant and equipment	5,199		5,199		4,656
Unamortized debt expense	20		20		$ 23
Right-of-use asset	164		164
Change in accrued expenditures	(53)	(31)	52	21
Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	304	594	1,127	1,708
E&P
Segment Reporting Information [Line Items]
Total operating revenues	357	639	1,288	1,809
Depreciation, depletion and amortization expense	123	140	345	383
Impairments	0	15	6	15
Operating Income (Loss)	(21)	175	219	510
Interest expense	17	29	46	100
Gain (Loss) on Derivatives	100	(65)	220	(108)
Gain (Loss) on early extinguishment of debt	0		0	0
Other (loss) income, Net	(4)	0	(8)	3
Provision (benefit) for income taxes	10		(401)
Assets	6,099	5,732	6,099	5,732
Capital investments	239	295	931	1,025
Restructuring charges	4	2	9	18
Assets held for sale		106		106
E&P | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	(9)	(6)	(27)	(19)
Midstream
Segment Reporting Information [Line Items]
Total operating revenues	279	312	1,005	878
Depreciation, depletion and amortization expense	2	11	7	43
Impairments	2	145	2	155
Operating Income (Loss)	(8)	(108)	(13)	(64)
Interest expense	0	0	0	0
Gain (Loss) on Derivatives	0	0	0	0
Gain (Loss) on early extinguishment of debt	0		0	0
Other (loss) income, Net	0	(1)	0	(2)
Provision (benefit) for income taxes	0		0
Assets	272	1,115	272	1,115
Capital investments	0	0	0	9
Restructuring charges				2
Assets held for sale		738		738
Midstream | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	313	600	1,154	1,727
Other
Segment Reporting Information [Line Items]
Total operating revenues	0	0	0	0
Depreciation, depletion and amortization expense	0	0	0	0
Impairments	0	1	0	1
Operating Income (Loss)	0	(1)	0	(1)
Interest expense	0	0	0	0
Gain (Loss) on Derivatives	0	0	0	0
Gain (Loss) on early extinguishment of debt	7		7	(8)
Other (loss) income, Net	2	0	1	0
Provision (benefit) for income taxes	0		0
Assets	227	211	227	211
Capital investments	1	3	2	5
Cash and cash equivalents	29	9	29	9
Income tax receivable	61	89	61	89
Property, plant and equipment	31	69	31	69
Unamortized debt expense	12	12	12	12
Prepayments	7	12	7	12
Non-qualified retirement plan	7	8	7	8
Right-of-use asset	84		84
Other | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	0	0	0	0
Marketing
Segment Reporting Information [Line Items]
Total operating revenues	279	287	1,004	805
Marketing | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	313	559	1,154	1,598
Marketing | Midstream | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	$ 313	$ 559	$ 1,154	1,598
Non-Core Gathering Assets | Midstream
Segment Reporting Information [Line Items]
Impairments				$ 10