Income Taxes - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Tax Credit Carryforward [Line Items]
Income tax benefit resulting from refund		$ 120,000	$ 141,000	$ 65,000
Current state expense			16,000
Amount offset by current expense			435,000	29,000
Federal tax reform benefit		0	(5,288)	$ 1,205,140
Tax credit carryforward, valuation allowance, Reversal	$ 13,000
Income taxes receivable, current		298,854	131,573
Expected refund for alternative minimum tax credits		95,000	$ 190,000
Expected refund for net operating loss carryback claims		14,000
Tax credit carryforward, amount		$ 95,000
Statutory income tax rate		21.00%	21.00%	35.00%
Income tax expense from government regulated asset				$ 10,500
Effective tax rate, amount		$ 150,900	$ 124,600	120,500
Release due to settlement		84,000
DTA, decrease resulting from uncertain tax positions				300
Tax positions for which the ultimate deductibility is highly certain		700	700	4,700
Interest expense		3,300	3,400	3,200
Interests and penalties		15,200	11,900	8,400
Decrease in unrecognized tax benefits is reasonably possible		80,200	33,300	42,500
Deferred tax liability, disposition of business		337,600
Operating loss carryforward, valuation allowances				217,000
Deferred tax asset, valuation allowances		423,444	351,408
Interest disallowance limitation, valuation Allowance			21,700
Valuation allowance			13,300
Net operating loss carryforwards				130,000
Decrease from deconsolidation		(90,889)	4,388,341
Equitrans Midstream
Tax Credit Carryforward [Line Items]
Operating loss carryforward, valuation allowances			14,000
Domestic Tax Authority
Tax Credit Carryforward [Line Items]
Operating loss carryforwards		218,800	32,900
Operating loss carryforward, valuation allowances		22,800	22,800
Domestic Tax Authority | Equity Securities, FN-NI, Valuation Allowance
Tax Credit Carryforward [Line Items]
Deferred tax asset, valuation allowances		8,300
State and Local Jurisdiction
Tax Credit Carryforward [Line Items]
Operating loss carryforward, valuation allowances		324,100	279,500
Deferred tax asset, NOL, state and local		416,700	94,700
State and Local Jurisdiction | Property, Plant and Equipment
Tax Credit Carryforward [Line Items]
Deferred tax asset, valuation allowances		4,500
State and Local Jurisdiction | Tax Cuts and Jobs Act Interest Deduction
Tax Credit Carryforward [Line Items]
Deferred tax asset, valuation allowances		21,300
State and Local Jurisdiction | Equity Securities, FN-NI, Valuation Allowance
Tax Credit Carryforward [Line Items]
Deferred tax asset, valuation allowances		42,400
Deferred Tax Assets
Tax Credit Carryforward [Line Items]
Uncertain tax positions		$ 113,700	$ 88,200	84,100
Federal Marginal Well Tax Credit
Tax Credit Carryforward [Line Items]
Tax credit carryforward, amount				30,200
Federal Marginal Well Tax Credit | Tax Year 2016
Tax Credit Carryforward [Line Items]
Tax credit carryforward, amount				$ 6,100