Investment in Nonconsolidated Entity (Details) $ in Millions	1 Months Ended				6 Months Ended
	Sep. 30, 2018 USD ($)	Jul. 31, 2018 USD ($)	May 31, 2018 USD ($)	Apr. 30, 2018 USD ($)	Jun. 30, 2018 USD ($) mi	Dec. 31, 2020 mi
Schedule of Equity Method Investments [Line Items]
Percent interest to require approval					66.67%
Issuance of performance guarantee					$ 91.0
Variable Interest Entity, Not Primary Beneficiary | MVP Joint Venture
Schedule of Equity Method Investments [Line Items]
Maximum financial statement exposure					$ 1,094.0
MVP Joint Venture
Schedule of Equity Method Investments [Line Items]
Capital call notice			$ 445.9
MVP Joint Venture | Scenario, Forecast
Schedule of Equity Method Investments [Line Items]
Capital call notice paid	$ 252.5
MVP Joint Venture | Subsequent Event
Schedule of Equity Method Investments [Line Items]
Capital call notice paid		$ 193.4
MVP Joint Venture | EQM
Schedule of Equity Method Investments [Line Items]
Ownership percentage					45.50%
Mountain Valley Pipeline
Schedule of Equity Method Investments [Line Items]
Natural gas interstate pipeline (in miles) | mi					300
Mountain Valley Pipeline | Minimum
Schedule of Equity Method Investments [Line Items]
Estimated project cost				$ 3,500.0
Mountain Valley Pipeline | Maximum
Schedule of Equity Method Investments [Line Items]
Estimated project cost				3,700.0
MVP Southgate Project | Minimum
Schedule of Equity Method Investments [Line Items]
Estimated project cost				350.0
MVP Southgate Project | Maximum
Schedule of Equity Method Investments [Line Items]
Estimated project cost				$ 500.0
MVP Southgate Project | Scenario, Forecast
Schedule of Equity Method Investments [Line Items]
Natural gas interstate pipeline (in miles) | mi						70
MVP Southgate Project | MVP Joint Venture | EQM | Scenario, Forecast | Minimum
Schedule of Equity Method Investments [Line Items]
Ownership percentage						33.00%
MVP Southgate Project | MVP Joint Venture | EQM | Scenario, Forecast | Maximum
Schedule of Equity Method Investments [Line Items]
Ownership percentage						48.00%