Investment in Nonconsolidated Entity (Details) $ in Millions		1 Months Ended		3 Months Ended		9 Months Ended
	Nov. 15, 2017 USD ($)	Oct. 31, 2017 USD ($)	Aug. 31, 2017 USD ($)	Sep. 30, 2017 USD ($) mi	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) Bcf / d mi	Sep. 30, 2016 USD ($)
Schedule of Equity Method Investments [Line Items]
Percent interest to require approval						66.67%
Issuance of performance guarantee				$ 91.0		$ 91.0
Mountain Valley Pipeline
Schedule of Equity Method Investments [Line Items]
Natural gas interstate pipeline (in miles) | mi				300		300
MVP Joint Venture
Schedule of Equity Method Investments [Line Items]
Firms capacity commitments per day (in bcf per day) | Bcf / d						2.0
Duration of firm capacity commitments (in years)						20 years
EQM
Schedule of Equity Method Investments [Line Items]
Total investments				$ 6.0	$ 2.7	$ 15.4	$ 6.1
EQT Corporation and Subsidiaries | MVP Joint Venture
Schedule of Equity Method Investments [Line Items]
Firms capacity commitments per day (in bcf per day) | Bcf / d						1.29
MVP Joint Venture
Schedule of Equity Method Investments [Line Items]
Capital call notice			$ 48.0
MVP Joint Venture | Scenario, Forecast
Schedule of Equity Method Investments [Line Items]
Payments to acquire equity method investments	$ 20.8
MVP Joint Venture | Subsequent Event
Schedule of Equity Method Investments [Line Items]
Payments to acquire equity method investments		$ 27.2
Variable Interest Entity, Not Primary Beneficiary | MVP Joint Venture
Schedule of Equity Method Investments [Line Items]
Maximum financial statement exposure				$ 431.0		$ 431.0
Variable Interest Entity, Not Primary Beneficiary | MVP Joint Venture | Mountain Valley Pipeline
Schedule of Equity Method Investments [Line Items]
Percentage of remaining obligations						33.00%
Variable Interest Entity, Not Primary Beneficiary | EQM | MVP Joint Venture
Schedule of Equity Method Investments [Line Items]
Ownership percentage				45.50%		45.50%