Revenue Recognition (Disaggregation of Revenue on Geographic Basis) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 592	$ 990
E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	353	551
Operating Segments | E&P
Disaggregation of Revenue [Line Items]
Total operating revenues	344	542
Operating Segments | E&P | Northeast Appalachia
Disaggregation of Revenue [Line Items]
Total operating revenues	195	348
Operating Segments | E&P | Southwest Appalachia
Disaggregation of Revenue [Line Items]
Total operating revenues	149	193
Operating Segments | E&P | Other
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 0	$ 1