Debt - Schedule of Long-Term Debt (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Oct. 31, 2017
Debt Instrument [Line Items]
Principal Value	$ 4,724,920,000	$ 4,737,327,000
Carrying Value	4,697,381,000	4,702,329,000
Fair Value	4,553,427,000	4,872,831,000
Debt payable within one year, principal value	704,661,000	12,407,000
Debt payable within one year, carrying value	704,390,000	12,406,000
Debt payable within one year, fair value	717,609,000	12,932,000
Total long-term debt, principal value	4,020,259,000	4,724,920,000
Total long-term debt, carrying value	3,992,991,000	4,689,923,000
Total long-term debt, fair value	3,835,818,000	4,859,899,000
8.13% Notes, due June 1, 2019
Debt Instrument [Line Items]
Principal Value	700,000,000	700,000,000
Carrying Value	699,729,000	698,918,000
Fair Value	$ 712,663,000	755,153,000
Interest rate	8.13%
Floating Rate Notes due October 1, 2020
Debt Instrument [Line Items]
Principal Value	$ 500,000,000	500,000,000	$ 500,000,000
Carrying Value	498,222,000	497,206,000
Fair Value	490,730,000	501,325,000
2.50% Notes due October 1, 2020
Debt Instrument [Line Items]
Principal Value	500,000,000	500,000,000	500,000,000
Carrying Value	498,198,000	497,169,000
Fair Value	$ 489,690,000	497,670,000
Interest rate	2.50%
4.88% Notes, due November 15, 2021
Debt Instrument [Line Items]
Principal Value	$ 750,000,000	750,000,000
Carrying Value	746,245,000	744,920,000
Fair Value	$ 762,555,000	801,953,000
Interest rate	4.88%
3.00% Notes due October 1, 2022
Debt Instrument [Line Items]
Principal Value	$ 750,000,000	750,000,000	750,000,000
Carrying Value	743,972,000	742,364,000
Fair Value	$ 712,980,000	743,550,000
Interest rate	3.00%
7.75% debentures, due July 15, 2026
Debt Instrument [Line Items]
Principal Value	$ 115,000,000	115,000,000
Carrying Value	111,229,000	110,732,000
Fair Value	$ 128,808,000	135,024,000
Interest rate	7.75%
3.90% Notes due October 1, 2027
Debt Instrument [Line Items]
Principal Value	$ 1,250,000,000	1,250,000,000	$ 1,250,000,000
Carrying Value	1,239,866,000	1,238,707,000
Fair Value	$ 1,085,663,000	1,245,200,000
Interest rate	3.90%
7.42% Series B, due 2023
Debt Instrument [Line Items]
Principal Value	$ 10,000,000	10,000,000
Carrying Value	10,000,000	10,000,000
Fair Value	$ 10,666,000	11,433,000
Interest rate	7.42%
7.6% Series C, due 2018
Debt Instrument [Line Items]
Principal Value	$ 0	8,000,000
Carrying Value	0	7,999,000
Fair Value	$ 0	8,012,000
Interest rate	7.60%
8.8% to 9.0% Series A, due 2020 through 2021
Debt Instrument [Line Items]
Principal Value	$ 35,200,000	35,200,000
Carrying Value	35,200,000	35,187,000
Fair Value	$ 37,920,000	40,510,000
8.8% to 9.0% Series A, due 2020 through 2021 \| Minimum
Debt Instrument [Line Items]
Interest rate	8.80%
8.8% to 9.0% Series A, due 2020 through 2021 \| Maximum
Debt Instrument [Line Items]
Interest rate	9.00%
EQT Midstream Notes
Debt Instrument [Line Items]
Principal Value	$ 114,720,000	119,127,000
Carrying Value	114,720,000	119,127,000
Fair Value	$ 121,752,000	$ 133,001,000

Debt Instrument, Face Amount, Current

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Long-term Debt, Fair Value, Current

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Face (par) amount of debt instrument at time of issuance.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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