Revenue Recognition (Disaggregation of Revenue by Segment) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 636	$ 951	$ 2,293	$ 2,687
E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	357	639	1,288	1,809
Midstream
Disaggregation of Revenue [Line Items]
Total operating revenues	279	312	1,005	878
Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	348	633	1,261	1,790
Operating Segments | Midstream
Disaggregation of Revenue [Line Items]
Total operating revenues	592	912	2,159	2,605
Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	304	594	1,127	1,708
Intersegment Revenues | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	(9)	(6)	(27)	(19)
Intersegment Revenues | Midstream
Disaggregation of Revenue [Line Items]
Total operating revenues	313	600	1,154	1,727
Gas sales
Disaggregation of Revenue [Line Items]
Total operating revenues	238	465	943	1,412
Gas sales | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	230	460	918	1,395
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)	(5)	(25)	(17)
Oil sales
Disaggregation of Revenue [Line Items]
Total operating revenues	67	62	153	141
Oil sales | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	66	61	151	139
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)	(1)	(2)	(2)
NGL sales
Disaggregation of Revenue [Line Items]
Total operating revenues	52	112	191	252
NGL sales | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	52	112	191	252
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	279	287	1,004	805
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	592	846	2,158	2,403
Marketing | Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	313	559	1,154	1,598
Marketing | Intersegment Revenues | Midstream
Disaggregation of Revenue [Line Items]
Total operating revenues	313	559	1,154	1,598
Gas gathering
Disaggregation of Revenue [Line Items]
Total operating revenues	0	25	0	73
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		66		202
Gas gathering | Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		41		129
Other
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 0	$ 0	2	4
Other | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues			1	4
Other | Operating Segments | Midstream
Disaggregation of Revenue [Line Items]
Total operating revenues			1	0
Other | Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues			$ 0	$ 0