Share-Based Compensation Plans - Summary of Restricted Stock Activity (Details) - Restricted Stock - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Non- Vested Shares
Non-vested shares, outstanding, beginning balance (in shares)	310,997
Non-vested shares, granted (in shares)	1,767,960
Non-vested shares, vested (in shares)	(130,487)
Non-vested shares, forfeited (in shares)	(80,070)
Non-vested shares, outstanding, ending balance (in shares)	1,868,400	310,997
Weighted Average Fair Value
Weighted average fair value, outstanding, beginning balance (in dollars per share)	$ 25.47
Weighted average fair value, granted (in dollars per share)	10.02
Weighted average fair value, vested (in dollars per share)	24.26
Weighted average fair value, forfeited (in dollars per share)	10.90
Weighted average fair value, outstanding, ending balance (in dollars per share)	$ 11.56	$ 25.47
Aggregate Fair Value
Aggregate fair value, outstanding, beginning balance	$ 7,921,313
Aggregate fair value, granted	17,711,033
Aggregate fair value, vested	(3,165,269)	$ (11,900,000)	$ (39,800,000)
Aggregate fair value, forfeited	(872,763)
Aggregate fair value, outstanding, ending balance	$ 21,594,314	$ 7,921,313
Equitrans Midstream Employees
Non- Vested Shares
Non-vested shares, outstanding, ending balance (in shares)	59,340