Revolving Credit Facilities (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
EQM
Line of Credit Facility
Line of credit facility, maximum borrowing capacity	$ 1,000,000,000
Revolving credit facility | EQM
Line of Credit Facility
Amount of borrowings	317,000,000	$ 0	$ 180,000,000
Letters of credit outstanding under revolving credit facility	0	0	0
Maximum amount of outstanding short-term loans at any time during the period	420,000,000	0
Average daily balance of short-term loans outstanding during the period	$ 301,000,000
Weighted average interest rates of average daily balance of short-term loans	3.00%
Revolving credit facility | EQT 2.5 Billion Facility
Line of Credit Facility
Line of credit facility, maximum borrowing capacity	$ 2,500,000,000.0
Amount of borrowings	1,300,000,000	0	1,300,000,000
Letters of credit outstanding under revolving credit facility	0	0	159,400,000
Maximum amount of outstanding short-term loans at any time during the period	1,600,000,000	$ 0
Average daily balance of short-term loans outstanding during the period	$ 1,400,000,000
Weighted average interest rates of average daily balance of short-term loans	3.10%
Revolving credit facility | RMP $850 Million Facility
Line of Credit Facility
Line of credit facility, maximum borrowing capacity	$ 850,000,000
Amount of borrowings	325,000,000		286,000,000
Letters of credit outstanding under revolving credit facility	1,000,000		$ 1,000,000
Maximum amount of outstanding short-term loans at any time during the period	336,000,000
Average daily balance of short-term loans outstanding during the period	$ 308,000,000
Weighted average interest rates of average daily balance of short-term loans	3.60%