Revenue Recognition (Disaggregation of Revenue on Geographic Basis) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Operating revenues, including intersegment revenue	$ 2,525	$ 2,086	$ 1,413
Northeast Appalachia [Member]
Disaggregation of Revenue [Line Items]
Operating revenues, including intersegment revenue	1,165	837	470
Southwest Appalachia [Member]
Disaggregation of Revenue [Line Items]
Operating revenues, including intersegment revenue	817	498	259
Fayetteville Shale [Member]
Disaggregation of Revenue [Line Items]
Operating revenues, including intersegment revenue	537	743	675
Other Property [Member]
Disaggregation of Revenue [Line Items]
Operating revenues, including intersegment revenue	$ 6	$ 8	$ 9