Revolving Credit Facilities (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Line of Credit Facility
Revolving credit facility outstanding amount at the end of period		$ 0		$ 0	$ 0
Letter of credit outstanding amount at the end of period	0		0		0
Revolving credit facility maximum borrowing capacity	1,500		1,500		1,500
Commitment fee paid to maintain credit facility (as a percent)	0.06%	0.05%	0.18%	0.19%
Maximum amount of outstanding short-term loans at any time during the period	140.5		178.5
Average daily balance of short-term loans outstanding during the period	21.5		16.1
Weighted average interest rates of average daily balance of short-term loans (as a percent)	0.60%		0.70%
EQT Midstream Partners
Line of Credit Facility
Revolving credit facility outstanding amount at the end of period	0		0		0
Letter of credit outstanding amount at the end of period	0		0		0
Revolving credit facility maximum borrowing capacity	350		350		350
Commitment fee paid to maintain credit facility (as a percent)	0.06%	0.06%	0.19%
Maximum amount of outstanding short-term loans at any time during the period	$ 0	$ 0	$ 0	$ 0