Organization and Summary of Significant Accounting Policies (Schedule of Supplemental Disclosures of Cash Flow Information) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Cash paid during the year for interest, net of amounts capitalized	$ 75	$ 58	$ 135
Cash paid (received) during the year for income taxes	(32)	(52)	6
Increase (decrease) in noncash property additions	1,084	$ 41	$ (42)
Montage Resources Corporation
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Increase (decrease) in noncash property additions	$ 1,097