Segment Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Total operating revenues	$ 990	$ 920
Depreciation, depletion and amortization expense	112	143
Operating income	213	255
Interest expense	14	39
Loss on Derivatives	(32)	(7)
Other Income (Loss), Net	1	(1)
Benefit for income taxes	(426)	0
Assets	6,446	7,713	$ 5,797
Capital investments	325	338
Restructuring charges	3	0
Cash and cash equivalents	366		$ 201
Change in accrued expenditures	66	33
Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	493	613
E&P
Segment Reporting Information [Line Items]
Total operating revenues	551	643
Depreciation, depletion and amortization expense	110	117
Operating income	210	238
Interest expense	14	39
Loss on Derivatives	(32)	(7)
Other Income (Loss), Net	1	0
Benefit for income taxes	(426)
Assets	5,562	5,346
Capital investments	325	334
Restructuring charges	3
E&P | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	(9)	(6)
Midstream
Segment Reporting Information [Line Items]
Total operating revenues	439	277
Depreciation, depletion and amortization expense	2	26
Operating income	3	17
Interest expense	0	0
Loss on Derivatives	0	0
Other Income (Loss), Net	0	(1)
Benefit for income taxes	0
Assets	342	1,217
Capital investments	0	4
Midstream | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	502	619
Other
Segment Reporting Information [Line Items]
Total operating revenues	0	0
Depreciation, depletion and amortization expense	0	0
Operating income	0	0
Interest expense	0	0
Loss on Derivatives	0	0
Other Income (Loss), Net	0	0
Benefit for income taxes	0
Assets	542	1,150
Capital investments	0	0
Cash and cash equivalents	366	958
Other | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	0	0
Marketing
Segment Reporting Information [Line Items]
Total operating revenues	438	253
Marketing | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	502	576
Marketing | Midstream | Intersegment Revenues
Segment Reporting Information [Line Items]
Total operating revenues	$ 502	576
Non-Core Gathering Assets | Midstream
Segment Reporting Information [Line Items]
Impairments		$ 10