Natural Gas and Oil Properties (Narrative) (Details)	3 Months Ended
	Mar. 31, 2021 USD ($) derivative_position $ / MMBTU $ / bbl	Mar. 31, 2020 USD ($) $ / bbl $ / MMBTU
Natural Gas and Oil Properties [Line Items]
Natural gas, oil and NGL reserves discount	10.00%
Period of time needed to calculate ceiling value of reserves	12 months
Number of hedge positions designated for hedge accounting | derivative_position	0
Impairments	$ 0	$ 1,479,000,000
Net book value adjusted for market differentials		$ 1,500,000,000
Montage Resources Corporation
Natural Gas and Oil Properties [Line Items]
Impairments	0
Unamortized cost of properties acquired	1,102,000,000
Montage Resources Corporation | Pro Forma
Natural Gas and Oil Properties [Line Items]
Impairments	$ 0
Natural Gas
Natural Gas and Oil Properties [Line Items]
Full cost ceiling test, price per MMBtu (in dollars per MMBtu) | $ / MMBTU	2.16	2.30
Oil
Natural Gas and Oil Properties [Line Items]
Full cost ceiling test, price per barrel (in dollars per bbl) | $ / bbl	40.01	55.77
NGL
Natural Gas and Oil Properties [Line Items]
Full cost ceiling test, price per barrel (in dollars per bbl) | $ / bbl	13.57	9.96