Revenue Recognition (Disaggregation of Revenue on Geographic Basis) (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
Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	704	211	1,409	555
Operating Segments | E&P | Northeast Appalachia
Disaggregation of Revenue [Line Items]
Total operating revenues	230	117	493	312
Operating Segments | E&P | Southwest Appalachia
Disaggregation of Revenue [Line Items]
Total operating revenues	474	94	915	243
Operating Segments | E&P | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 0	$ 0	$ 1	$ 0