Revenue Recognition (Disaggregation of Revenue by Segment) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 667	$ 816	$ 1,657	$ 1,736
E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	380	527	931	1,170
Midstream
Disaggregation of Revenue [Line Items]
Total operating revenues	287	289	726	566
Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	371	520	913	1,157
Operating Segments | Midstream
Disaggregation of Revenue [Line Items]
Total operating revenues	626	797	1,567	1,693
Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	330	501	823	1,114
Intersegment Revenues | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	(9)	(7)	(18)	(13)
Intersegment Revenues | Midstream
Disaggregation of Revenue [Line Items]
Total operating revenues	339	508	841	1,127
Gas sales
Disaggregation of Revenue [Line Items]
Total operating revenues	275	407	705	947
Gas sales | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	267	400	688	935
Gas sales | Operating Segments | Midstream
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0	0	0
Gas sales | Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	(8)	(7)	(17)	(12)
Oil sales
Disaggregation of Revenue [Line Items]
Total operating revenues	47	44	86	79
Oil sales | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	46	44	85	78
Oil sales | Operating Segments | Midstream
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0	0	0
Oil sales | Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	(1)	0	(1)	(1)
NGL sales
Disaggregation of Revenue [Line Items]
Total operating revenues	58	75	139	140
NGL sales | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	58	75	139	140
NGL sales | Operating Segments | Midstream
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0	0	0
NGL sales | Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0	0	0
Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	287	265	725	518
Marketing | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0	0	0
Marketing | Operating Segments | Midstream
Disaggregation of Revenue [Line Items]
Total operating revenues	626	728	1,566	1,557
Marketing | Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	339	463	841	1,039
Marketing | Intersegment Revenues | Midstream
Disaggregation of Revenue [Line Items]
Total operating revenues	339	463	841	1,039
Gas gathering
Disaggregation of Revenue [Line Items]
Total operating revenues	0	24	0	48
Gas gathering | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues		0		0
Gas gathering | Operating Segments | Midstream
Disaggregation of Revenue [Line Items]
Total operating revenues		69		136
Gas gathering | Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		45		88
Other
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 0	1	2	4
Other | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues		1	1	4
Other | Operating Segments | Midstream
Disaggregation of Revenue [Line Items]
Total operating revenues		0	1	0
Other | Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		$ 0	$ 0	$ 0