Acquisition - (Schedule of Pro Forma) (Details) - Montage Resources Corporation and Indigo Natural Resources, LLC - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Business Acquisition [Line Items]
Revenues	$ 1,864	$ 844	$ 4,531	$ 2,388
Loss from continuing operations	$ (1,588)	$ (871)	$ (2,371)	$ (3,337)