Revenue Recognition (Disaggregation of Revenue by Segment) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 1,598	$ 527	$ 3,720	$ 1,529
E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	1,179	308	2,616	884
Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	419	219	1,104	645
Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	1,165	298	2,574	853
Operating Segments | Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	1,366	495	3,346	1,432
Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	933	266	2,200	756
Intersegment Revenues | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	(14)	(10)	(42)	(31)
Intersegment Revenues | Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	947	276	2,242	787
Gas sales
Disaggregation of Revenue [Line Items]
Total operating revenues	811	199	1,708	611
Gas sales | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	799	190	1,671	584
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	37	27
Oil sales
Disaggregation of Revenue [Line Items]
Total operating revenues	110	40	297	111
Oil sales | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	108	39	293	107
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	2	1	4	4
NGL sales
Disaggregation of Revenue [Line Items]
Total operating revenues	255	68	607	158
NGL sales | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	255	68	606	158
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	0	0	1	0
Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	418	219	1,102	645
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	1,365	495	3,344	1,432
Marketing | Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	947	276	2,242	787
Other
Disaggregation of Revenue [Line Items]
Total operating revenues	4	1	6	4
Other | Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	3	1	4	4
Other | Operating Segments | Marketing
Disaggregation of Revenue [Line Items]
Total operating revenues	1	0	2	0
Other | Intersegment Revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 0	$ 0	$ 0	$ 0