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Subsequent Event (Details) - Scenario, Forecast
shares in Millions
Nov. 12, 2018
shares
Equitrans Midstream  
Subsequent Event [Line Items]  
Percentage of ownership transferred 80.10%
Stock dividend, conversion ratio 0.80
Percentage of ownership after transaction 19.90%
Equitrans Midstream  
Subsequent Event [Line Items]  
Investment owned (in shares) 255