Natural Gas and Oil Properties (Narrative) (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) derivative_position $ / MMBTU $ / bbl	Jun. 30, 2020 USD ($) $ / bbl $ / MMBTU	Mar. 31, 2020 USD ($)
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	$ 655,000,000	$ 0	$ 2,134,000,000
Net book value adjusted for market differentials		$ 650,000,000		$ 650,000,000	$ 1,500,000,000
Montage Resources Corporation
Natural Gas and Oil Properties [Line Items]
Impairments			0
Unamortized cost of properties acquired	1,130,000,000		1,130,000,000
Montage Resources Corporation | Pro Forma
Natural Gas and Oil Properties [Line Items]
Impairments	$ 0		$ 0
Natural Gas
Natural Gas and Oil Properties [Line Items]
Full cost ceiling test, price per MMBtu (in dollars per MMBtu) | $ / MMBTU			2.43	2.07
Oil
Natural Gas and Oil Properties [Line Items]
Full cost ceiling test, price per barrel (in dollars per bbl) | $ / bbl			49.78	47.17
NGL
Natural Gas and Oil Properties [Line Items]
Full cost ceiling test, price per barrel (in dollars per bbl) | $ / bbl			17.06	8.87