Long-Term Debt - Schedule of Long-Term Debt (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Principal Value	$ 2,818,200,000	$ 2,988,900,000
Carrying Value	2,793,343,000	2,959,353,000
Fair Value	2,803,267,000	3,314,202,000
Debt payable within one year, principal value	0	166,011,000
Debt payable within one year, carrying value	0	(165,874,000)
Debt payable within one year, fair value	0	(171,081,000)
Total long-term debt, principal value	2,818,200,000	2,822,889,000
Total long-term debt, carrying value	2,793,343,000	2,793,479,000
Total long-term debt, fair value	2,803,267,000	3,143,121,000
7.76% notes, due 2015 through 2016
Debt Instrument [Line Items]
Principal Value	0	10,700,000
Carrying Value	0	10,700,000
Fair Value	$ 0	10,700,000
Interest rate	7.76%
5.00% notes, due October 1, 2015
Debt Instrument [Line Items]
Principal Value	$ 0	150,000,000
Carrying Value	0	149,865,000
Fair Value	$ 0	154,692,000
Interest rate	5.00%
5.15% notes, due March 1, 2018
Debt Instrument [Line Items]
Principal Value	$ 200,000,000	200,000,000
Carrying Value	199,156,000	198,766,000
Fair Value	$ 203,490,000	214,626,000
Interest rate	5.15%
6.50% notes, due April 1, 2018
Debt Instrument [Line Items]
Principal Value	$ 500,000,000	500,000,000
Carrying Value	498,360,000	497,630,000
Fair Value	$ 520,175,000	559,900,000
Interest rate	6.50%
8.13% notes, due June 1, 2019
Debt Instrument [Line Items]
Principal Value	$ 700,000,000	700,000,000
Carrying Value	697,295,000	696,483,000
Fair Value	$ 760,837,000	843,864,000
Interest rate	8.13%
4.88% notes, due November 15, 2021
Debt Instrument [Line Items]
Principal Value	$ 750,000,000	750,000,000
Carrying Value	742,270,000	740,945,000
Fair Value	$ 728,063,000	812,558,000
Interest rate	4.88%
7.75% debentures, due July 15, 2026
Debt Instrument [Line Items]
Principal Value	$ 115,000,000	115,000,000
Carrying Value	109,738,000	109,240,000
Fair Value	$ 119,372,000	147,036,000
Interest rate	7.75%
Medium-term notes, 7.3% to 7.6% Series B, due 2015 thru 2023
Debt Instrument [Line Items]
Principal Value	$ 10,000,000	20,000,000
Carrying Value	9,991,000	19,985,000
Fair Value	$ 10,241,000	22,279,000
Interest rate, minimum	7.30%
Interest rate, maximum	7.60%
Medium-term notes, 7.6% Series C, due 2018
Debt Instrument [Line Items]
Principal Value	$ 8,000,000	8,000,000
Carrying Value	7,983,000	7,975,000
Fair Value	$ 8,366,000	8,950,000
Interest rate	7.60%
Medium-term notes, 8.7% to 9.0% Series A, due 2020 thru 2021
Debt Instrument [Line Items]
Principal Value	$ 35,200,000	35,200,000
Carrying Value	35,149,000	35,131,000
Fair Value	$ 38,598,000	43,912,000
Interest rate, minimum	8.70%
Interest rate, maximum	9.00%
EQT Midstream | 4.00% EQM notes, due August 1, 2024
Debt Instrument [Line Items]
Principal Value	$ 500,000,000	500,000,000
Carrying Value	493,401,000	492,633,000
Fair Value	$ 414,125,000	$ 495,685,000
Interest rate	4.00%