Revolving Credit Facilities (Details) - Revolving credit facility - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Sep. 30, 2018	Dec. 31, 2017
EQM
Line of Credit Facility
Line of credit facility, maximum borrowing capacity	$ 1,000,000,000		$ 1,000,000,000
Amount of borrowings	0	$ 0	0	$ 0		$ 180,000,000
Letters of credit outstanding under revolving credit facility	0	0	0	0		0
Maximum amount of outstanding short-term loans at any time during the period	338,000,000	0	420,000,000	0
Average daily balance of short-term loans outstanding during the period	$ 122,000,000		$ 211,000,000
Weighted average interest rates of average daily balance of short-term loans	3.40%		3.20%
EQM | Scenario, Forecast
Line of Credit Facility
Line of credit facility, maximum borrowing capacity					$ 2,000,000,000
EQT 2.5 Billion Facility
Line of Credit Facility
Line of credit facility, maximum borrowing capacity	$ 2,500,000,000.0		$ 2,500,000,000.0
Amount of borrowings	200,000,000	0	200,000,000	0		1,300,000,000
Letters of credit outstanding under revolving credit facility	0	0	0	0		159,400,000
Maximum amount of outstanding short-term loans at any time during the period	1,500,000,000	$ 0	1,600,000,000	$ 0
Average daily balance of short-term loans outstanding during the period	$ 900,000,000		$ 1,200,000,000
Weighted average interest rates of average daily balance of short-term loans	3.40%		3.20%
RMP $850 Million Facility
Line of Credit Facility
Amount of borrowings	$ 260,000,000		$ 260,000,000			286,000,000
Letters of credit outstanding under revolving credit facility	1,000,000		1,000,000			$ 1,000,000
Maximum amount of outstanding short-term loans at any time during the period			375,000,000
Average daily balance of short-term loans outstanding during the period	$ 305,000,000		$ 306,000,000
Weighted average interest rates of average daily balance of short-term loans	3.90%		3.80%