Earnings Per Share (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended
	Aug. 31, 2020	Mar. 31, 2019
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Treasury stock acquired (in shares)		5,260,687
Treasury stock acquired		$ 21
Treasury stock acquired, average cost per share (in dollars per share)		$ 3.84
Montage Resources Corporation
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Offering price (in dollars per share)	$ 2.50
Montage Resources Corporation | Public Stock Offering
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Underwritten public offering of common stock (in shares)	63,250,000
Net proceeds from public offering	$ 152