Revenue Recognition (Disaggregation of Revenue by Segment) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 1,050	$ 410	$ 2,122	$ 1,002
E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	718	223	1,437	576
Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	332	187	685	426
Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	704	211	1,409	555
Operating Segments | Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	983	389	1,980	937
Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	637	190	1,267	490
Intersegment Revenues | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	(14)	(12)	(28)	(21)
Intersegment Revenues | Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	651	202	1,295	511
Gas sales
Disaggregation of Revenue [Line Items]
Total operating revenues	433	164	897	412
Gas sales | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	421	155	872	394
Gas sales | Operating Segments | Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0	0	0
Gas sales | Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	12	9	25	18
Oil sales
Disaggregation of Revenue [Line Items]
Total operating revenues	106	19	187	71
Oil sales | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	105	16	185	68
Oil sales | Operating Segments | Marketing
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	3	2	3
NGL sales
Disaggregation of Revenue [Line Items]
Total operating revenues	179	40	352	90
NGL sales | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	178	40	351	90
NGL sales | Operating Segments | Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0	0	0
NGL sales | Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	1	0	1	0
Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	332	187	684	426
Marketing | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	0	0	0	0
Marketing | Operating Segments | Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	983	389	1,979	937
Marketing | Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	651	202	1,295	511
Other
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 0	$ 0	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