Revenue Recognition (Disaggregation of Revenue by Segment) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 1,072	$ 592
E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	719	353
Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	353	239
Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	705	344
Operating Segments | Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	997	548
Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	630	300
Intersegment Revenues | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	(14)	(9)
Intersegment Revenues | Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	644	309
Gas sales
Disaggregation of Revenue [Line Items]
Total operating revenues	464	248
Gas sales | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	451	239
Gas sales | Operating Segments | Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Gas sales | Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	(13)	(9)
Oil sales
Disaggregation of Revenue [Line Items]
Total operating revenues	81	52
Oil sales | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	80	52
Oil sales | Operating Segments | Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Oil sales | Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	(1)	0
NGL sales
Disaggregation of Revenue [Line Items]
Total operating revenues	173	50
NGL sales | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	173	50
NGL sales | Operating Segments | Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
NGL sales | Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	352	239
Marketing | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0
Marketing | Operating Segments | Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	996	548
Marketing | Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	644	309
Other
Disaggregation of Revenue [Line Items]
Total operating revenues	2	3
Other | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	1	3
Other | Operating Segments | Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	1	0
Other | Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 0	$ 0