EQM Midstream Partners 10-Q 30 Apr 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information	3 Months Ended
	Mar. 31, 2019shares
Entity Information [Line Items]
Entity Registrant Name	EQM Midstream Partners, LP
Entity Central Index Key	0001540947
Document Type	10-Q
Document Period End Date	Mar. 31, 2019
Amendment Flag	false
Current Fiscal Year End	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Small Business Entity	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Common Units
Entity Information [Line Items]
Entity Common Units, Unit Outstanding	200,457,630
Class B Units
Entity Information [Line Items]
Entity Common Units, Unit Outstanding	7,000,000

Statements of Consolidated Oper

Statements of Consolidated Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Operating revenues	[1],[2]	$ 389,782	$ 371,026
Operating expenses:
Operating and maintenance	[1],[3]	27,883	27,172
Selling, general and administrative	[1],[3]	32,920	26,390
Separation and other transaction costs	[1]	3,513	0
Depreciation	[1],[4]	47,065	41,280
Amortization of intangible assets	[1],[4]	10,387	10,386
Total operating expenses	[1]	121,768	105,228
Operating income	[1]	268,014	265,798
Equity income	[1],[4],[5]	31,063	8,811
Other income	[1]	2,210	904
Net interest expense	[1],[6]	49,356	12,670
Net income	[1],[7]	251,931	262,843
Net income attributable to noncontrolling interests	[1]	0	2,493
Net income attributable to EQM	[1]	251,931	260,350
Calculation of limited partner interest in net income:
Net income attributable to EQM	[1]	251,931	260,350
Less pre-acquisition net income allocated to EQT	[1]	0	(83,132)
Less general partner interest in net income – general partner units	[1]	0	(3,117)
Less general partner interest in net income – IDRs	[1]	0	(44,164)
Limited partner interest in net income	[1]	$ 251,931	$ 129,937
Net income per limited partner common unit – basic (in dollars per share)	[1]	$ 1.63	$ 1.61
Net income per limited partner common unit – diluted (in dollars per share)	[1]	$ 1.56	$ 1.61
Weighted average limited partner common units outstanding – basic (in shares)	[1]	154,259	80,607
Weighted average limited partner common units outstanding – diluted (in shares)	[1]	161,259	80,607
Cash distributions declared per unit (in dollars per share)	[1],[8]	$ 1.145	$ 1.065
[1]	As discussed in Notes 1 and 2, the consolidated financial statements of EQM have been retrospectively recast to include the pre-acquisition results of EQM Olympus Midstream LLC (EQM Olympus), Strike Force Midstream Holdings LLC (Strike Force) and EQM West Virginia Midstream LLC (EQM WV), which were acquired by EQM effective on May 1, 2018 (the Drop-Down Transaction), and Rice Midstream Partners LP (RMP), which was acquired by EQM effective on July 23, 2018 (the EQM-RMP Merger), because these transactions were between entities under common control
[2]	Operating revenues included related party revenues from EQT Corporation (NYSE: EQT) (EQT) of $284.5 million and $265.6 million for the three months ended March 31, 2019 and 2018, respectively. See Note 7.
[3]	For the three months ended March 31, 2019, operating and maintenance expense included $11.0 million of charges from Equitrans Midstream Corporation (Equitrans Midstream). For the three months ended March 31, 2018, operating and maintenance expense included charges from EQT of $12.2 million. For the three months ended March 31, 2019, selling, general and administrative expense included charges from Equitrans Midstream of $27.9 million. For the three months ended March 31, 2018, selling, general and administrative expense included charges from EQT of $23.8 million. See Note 7.
[4]	As discussed in Notes 1 and 2, the consolidated financial statements of EQM have been retrospectively recast to include the pre-acquisition results of the Drop-Down Transaction and the EQM-RMP Merger because these transactions were between entities under common control.
[5]	Represents equity income from Mountain Valley Pipeline, LLC (the MVP Joint Venture). See Note 8.
[6]	Net interest expense included interest income on the Preferred Interest in EQT Energy Supply, LLC (EES) of $1.6 million and $1.7 million for the three months ended March 31, 2019 and 2018, respectively.
[7]	As discussed in Notes 1 and 2, the consolidated financial statements of EQM have been retrospectively recast to include the pre-acquisition results of the Drop-Down Transaction and the EQM-RMP Merger because these transactions were between entities under common control.
[8]	Represents the cash distributions declared related to the period presented. See Note 11.

Statements of Consolidated Op_2

Statements of Consolidated Operations (Unaudited) (Parenthetical) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Operating and maintenance	[1],[2]	$ 27,883	$ 27,172
Selling, general and administrative expenses	[1],[2]	32,920	26,390
EQT
Operating revenues		284,500	265,600
Operating and maintenance			12,200
Selling, general and administrative expenses			23,800
EES
Interest income		1,600	$ 1,700
ETRN
Operating and maintenance		11,000
Selling, general and administrative expenses		$ 27,900
[1]	As discussed in Notes 1 and 2, the consolidated financial statements of EQM have been retrospectively recast to include the pre-acquisition results of EQM Olympus Midstream LLC (EQM Olympus), Strike Force Midstream Holdings LLC (Strike Force) and EQM West Virginia Midstream LLC (EQM WV), which were acquired by EQM effective on May 1, 2018 (the Drop-Down Transaction), and Rice Midstream Partners LP (RMP), which was acquired by EQM effective on July 23, 2018 (the EQM-RMP Merger), because these transactions were between entities under common control
[2]	For the three months ended March 31, 2019, operating and maintenance expense included $11.0 million of charges from Equitrans Midstream Corporation (Equitrans Midstream). For the three months ended March 31, 2018, operating and maintenance expense included charges from EQT of $12.2 million. For the three months ended March 31, 2019, selling, general and administrative expense included charges from Equitrans Midstream of $27.9 million. For the three months ended March 31, 2018, selling, general and administrative expense included charges from EQT of $23.8 million. See Note 7.

Statements of Consolidated Cash

Statements of Consolidated Cash Flows (Unaudited) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net income	[1],[2]	$ 251,931	$ 262,843
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	[1],[3]	47,065	41,280
Amortization of intangible assets	[1],[3]	10,387	10,386
Equity income	[1],[3],[4]	(31,063)	(8,811)
AFUDC – equity	[3]	(2,346)	(1,065)
Non-cash long-term compensation expense	[3]	255	499
Changes in other assets and liabilities:
Accounts receivable	[3]	(4,950)	(2,602)
Accounts payable	[3]	(72,188)	(14,145)
Other assets and other liabilities	[3]	(38,118)	(4,427)
Net cash provided by operating activities	[3]	160,973	283,958
Cash flows from investing activities:
Capital expenditures	[3]	(206,735)	(170,589)
Capital contributions to the MVP Joint Venture	[3]	(144,763)	(117,019)
Principal payments received on the Preferred Interest	[3]	1,141	1,079
Net cash used in investing activities	[3]	(350,357)	(286,529)
Cash flows from financing activities:
Proceeds from credit facility borrowings	[3]	602,000	304,000
Payments on credit facility borrowings	[3]	(145,000)	(128,000)
Distributions paid to unitholders	[3]	(211,292)	(158,735)
Distributions paid to noncontrolling interest	[3]	0	(750)
Capital contributions	[3]	0	12,873
Net cash provided by financing activities	[3]	245,708	29,388
Net change in cash, restricted cash and cash equivalents	[3]	56,324	26,817
Cash, restricted cash and cash equivalents at beginning of period	[3]	17,515	54,600
Cash, restricted cash and cash equivalents at end of period (b)	[3],[5]	73,839	81,417
Cash paid during the period for:
Interest, net of amount capitalized	[3]	88,240	13,532
Non-cash activity during the period for:
Decrease in capital contribution receivable from EQT	[3]	$ 0	$ (10,074)
[1]	As discussed in Notes 1 and 2, the consolidated financial statements of EQM have been retrospectively recast to include the pre-acquisition results of EQM Olympus Midstream LLC (EQM Olympus), Strike Force Midstream Holdings LLC (Strike Force) and EQM West Virginia Midstream LLC (EQM WV), which were acquired by EQM effective on May 1, 2018 (the Drop-Down Transaction), and Rice Midstream Partners LP (RMP), which was acquired by EQM effective on July 23, 2018 (the EQM-RMP Merger), because these transactions were between entities under common control
[2]	As discussed in Notes 1 and 2, the consolidated financial statements of EQM have been retrospectively recast to include the pre-acquisition results of the Drop-Down Transaction and the EQM-RMP Merger because these transactions were between entities under common control.
[3]	As discussed in Notes 1 and 2, the consolidated financial statements of EQM have been retrospectively recast to include the pre-acquisition results of the Drop-Down Transaction and the EQM-RMP Merger because these transactions were between entities under common control.
[4]	Represents equity income from Mountain Valley Pipeline, LLC (the MVP Joint Venture). See Note 8.
[5]	Includes $23.8 million of cash and cash equivalents and $50.0 million of cash escrowed as of March 31, 2019 associated with the Bolt-on Acquisition (as defined in Note 2).

Statements of Consolidated Ca_2

Statements of Consolidated Cash Flows (Unaudited) (Parenthetical) $ in Thousands	Mar. 31, 2019USD ($)
Cash and cash equivalents	$ 23,839
Bolt-on Acquisition
Cash and cash equivalents	23,800
Escrow deposit associated with Bolton-Acquisition	$ 50,000

Consolidated Balance Sheets (Un

Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands		Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents		$ 23,839	$ 17,515
Accounts receivable	[1]	259,340	254,390
Other current assets		13,286	14,909
Total current assets		296,465	286,814
Property, plant and equipment		6,639,047	6,367,530
Less: accumulated depreciation		(643,662)	(560,902)
Net property, plant and equipment	[1]	5,995,385	5,806,628
Investment in unconsolidated entity		1,673,325	1,510,289
Goodwill		1,123,813	1,123,813
Net intangible assets		565,726	576,113
Restricted cash	[2]	50,000	0
Other assets		183,871	152,464
Total assets		9,888,585	9,456,121
Current liabilities:
Accounts payable	[3]	143,186	207,877
Due to Equitrans Midstream		65,932	44,509
Capital contribution payable to the MVP Joint Venture		156,412	169,202
Accrued interest		41,302	80,199
Accrued liabilities		20,165	20,672
Total current liabilities		426,997	522,459
Credit facility borrowings		1,082,000	625,000
Senior notes		3,457,981	3,456,639
Regulatory and other long-term liabilities		67,414	38,724
Total liabilities		5,034,392	4,642,822
Equity:
General partner		0	29,626
Total equity	[4]	4,854,193	4,813,299
Total liabilities and equity		9,888,585	9,456,121
Common Units
Equity:
Common and Class B		4,852,205	4,783,673
Class B Units
Equity:
Common and Class B		$ 1,988	$ 0
[1]	Accounts receivable as of March 31, 2019 and December 31, 2018 included approximately $182.2 million and $174.8 million, respectively, of related party accounts receivable from EQT.
[2]	Includes $50.0 million of cash escrowed as of March 31, 2019 associated with the Bolt-on Acquisition (as defined in Note 2).
[3]	Accounts payable as of December 31, 2018 included approximately $34.0 million of related party accounts payable to EQT. There was no related party balance with EQT included in accounts payable as of March 31, 2019.
[4]	As discussed in Notes 1 and 2, the consolidated financial statements of EQM have been retrospectively recast to include the pre-acquisition results of the Drop-Down Transaction and the EQM-RMP Merger because these transactions were between entities under common control.

Consolidated Balance Sheets (_2

Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accounts receivable, for doubtful accounts	$ 792	$ 75
General partner, units issued (in shares)	0	1,443,015
General partner, units outstanding (in shares)	0	1,443,015
Accounts receivable, related parties	$ 182,200	$ 174,800
Accounts payable, related parties	$ 34,000
Common Units
Common units issued (in shares)	200,457,630	120,457,638
Common units outstanding (in shares)	200,457,630	120,457,638
Class B Units
Common units issued (in shares)	7,000,000	0
Common units outstanding (in shares)	7,000,000	0

Statements of Consolidated Equi

Statements of Consolidated Equity (Unaudited) - USD ($) $ in Thousands		Total		General Partner	Predecessor Equity	Noncontrolling Interest	Common UnitsLimited Partners	Class B UnitsLimited Partners
Beginning balance at Dec. 31, 2017	[1]	$ 6,238,864		$ 1,252	$ 3,916,434	$ 173,472	$ 2,147,706	$ 0
Increase (Decrease) in Partners' Capital
Net income	[1]	262,843	[2]	47,281	83,132	2,493	129,937
Capital contributions	[1]	2,799		50			2,749
Equity-based compensation plans	[1]	499			168		331
Distributions paid to unitholders	[1]	(158,735)		(43,294)	(32,845)		(82,596)
Net contributions from EQT	[2]	1,015			1,015
Distributions paid to noncontrolling interests		(750)				(750)
Ending balance at Mar. 31, 2018	[1]	6,346,535		5,289	3,967,904	175,215	2,198,127	0
Beginning balance at Dec. 31, 2018	[1]	4,813,299		29,626	0	0	4,783,673	0
Increase (Decrease) in Partners' Capital
Net income	[1]	251,931	[2]	1,767			246,699	3,465
Equity-based compensation plans	[1]	255					255
Distributions paid to unitholders	[1]	(211,292)		(75,175)			(136,117)
Equity restructuring associated with the EQM IDR Transaction				43,782			(42,305)	(1,477)
Ending balance at Mar. 31, 2019	[1]	$ 4,854,193		$ 0	$ 0	$ 0	$ 4,852,205	$ 1,988
[1]	As discussed in Notes 1 and 2, the consolidated financial statements of EQM have been retrospectively recast to include the pre-acquisition results of the Drop-Down Transaction and the EQM-RMP Merger because these transactions were between entities under common control.
[2]	As discussed in Notes 1 and 2, the consolidated financial statements of EQM have been retrospectively recast to include the pre-acquisition results of EQM Olympus Midstream LLC (EQM Olympus), Strike Force Midstream Holdings LLC (Strike Force) and EQM West Virginia Midstream LLC (EQM WV), which were acquired by EQM effective on May 1, 2018 (the Drop-Down Transaction), and Rice Midstream Partners LP (RMP), which was acquired by EQM effective on July 23, 2018 (the EQM-RMP Merger), because these transactions were between entities under common control

Statements of Consolidated Eq_2

Statements of Consolidated Equity (Unaudited) (Parenthetical) - $ / shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Stockholders' Equity [Abstract]
Distributions paid to unitholders (dollars per common unit)	$ 1.13	$ 1.025

Financial Statements

Financial Statements	3 Months Ended
	Mar. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Financial Statements	Financial Statements Organization and Basis of Presentation EQM is a growth-oriented Delaware limited partnership formed by EQT in January 2012. Prior to the completion of the EQM IDR Transaction (defined below), EQM Midstream Services, LLC was a direct, wholly-owned subsidiary of EQGP Holdings, LP (EQGP) and was the general partner of EQM (the Former EQM General Partner). Following the consummation of the EQM IDR Transaction, EQGP Services, LLC, a wholly-owned indirect subsidiary of Equitrans Midstream, became the general partner of EQM (the New EQM General Partner). References in these consolidated financial statements to Equitrans Midstream refer collectively to Equitrans Midstream Corporation and its consolidated subsidiaries. On February 21, 2018, EQT announced its plan to separate its midstream business, which was composed of the separately-operated natural gas gathering, transmission and storage and water services operations of EQT (collectively, the Midstream Business), from its upstream business, which was composed of the natural gas, oil and natural gas liquids development, production and sales and commercial operations of EQT (collectively, the Upstream Business) (the Separation). On November 12, 2018, the Separation was effected through a series of transactions that culminated in EQT's contribution of the Midstream Business to Equitrans Midstream. On February 22, 2019, Equitrans Midstream completed its previously announced simplification transaction pursuant to that certain Agreement and Plan of Merger, dated as of February 13, 2019 (the IDR Merger Agreement), by and among Equitrans Midstream, EQM, the Former EQM General Partner, EQGP, the New EQM General Partner, Equitrans Merger Sub, LP, a Delaware limited partnership (Merger Sub), and certain other parties thereto. Pursuant to the IDR Merger Agreement, on February 22, 2019, (i) Merger Sub merged with and into EQGP (the Merger) with EQGP continuing as the surviving limited partnership and a wholly-owned subsidiary of EQM following the Merger, and (ii) each of (a) the incentive distribution rights (IDRs) in EQM, (b) the economic portion of the general partner interest in EQM and (c) the issued and outstanding common units representing limited partner interests in EQGP were canceled, and, as consideration for such cancellation, certain affiliates of Equitrans Midstream received on a pro rata basis 80,000,000 newly-issued EQM common units and 7,000,000 newly-issued Class B units (Class B units), both representing limited partner interests in EQM, and the New EQM General Partner retained the non-economic general partner interest in EQM (the EQM IDR Transaction). Additionally as part of the EQM IDR Transaction, the 21,811,643 EQM common units held by EQGP were canceled and 21,811,643 EQM common units were issued pro rata to certain affiliates of Equitrans Midstream. Following the EQM IDR Transaction, Equitrans Midstream continued to hold investments in the entities conducting the Midstream Business, which, following the EQM IDR Transaction and as of March 31, 2019, represented a 59.9% limited partner interest and the non-economic general partner interest in EQM. See Note 4 for further information. The EQM IDR Transaction constituted an exchange of equity interests between entities under common control and not a transfer of a business. Therefore, the exchange resulted in a reclassification, as of February 22, 2019, of a $43.8 million deficit capital balance from the general partner line item to the common and Class B line items in EQM's consolidated balance sheets based on the respective limited partner ownership interests. The reclassification represented an allocation of the carrying value of the exchanged general partner interest. Prior to the EQM IDR Transaction, when distributions related to the general partner interest and IDRs were made, earnings equal to the amount of distributions were allocated to the general partner before the remaining earnings were allocated to the limited partner unitholders based on their respective ownership percentages. Subsequent to the EQM IDR Transaction, no earnings will be allocated to the general partner. The allocation of net income attributable to EQM for purposes of calculating net income per limited partner unit is described in Note 11 . EQM's consolidated financial statements have been retrospectively recast to include the pre-acquisition results of the Drop-Down Transaction and the EQM-RMP Merger because these transactions represented business combinations between entities under common control. The recast is for the period the acquired businesses were under the common control of EQT, which began on November 13, 2017 as a result of EQT's acquisition of Rice Energy Inc. (Rice) (the Rice Merger). EQM recorded the assets and liabilities acquired in the Drop-Down Transaction and the EQM-RMP Merger at their carrying amounts to EQT on the effective dates of the transactions. The consolidated financial statements are not necessarily indicative of the actual results of operations if EQM and the assets acquired in the Drop-Down Transaction and the EQM-RMP Merger had been operated together during the pre-acquisition periods. The accompanying unaudited consolidated financial statements have been prepared in accordance with GAAP for interim financial information and with the requirements of Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of management, these unaudited consolidated financial statements include all adjustments (consisting of only normal recurring adjustments, unless otherwise disclosed in this Form 10-Q) necessary for a fair presentation of the financial position of EQM as of March 31, 2019 and December 31, 2018 and the results of its operations, cash flows and equity for the three months ended March 31, 2019 and 2018 . The balance sheet at December 31, 2018 has been derived from the audited financial statements at that date but does not include all of the information and footnotes required by GAAP for complete financial statements. Due to the seasonal nature of EQM's utility customer contracts, the interim statements for the three months ended March 31, 2019 are not necessarily indicative of the results that may be expected for the year ending December 31, 2019 . EQM does not have any employees. Operational, management and other services for EQM are provided by the directors and officers of the New EQM General Partner and employees of Equitrans Midstream. For further information, refer to the consolidated financial statements and related footnotes for the year ended December 31, 2018, as well as "Management's Discussion and Analysis of Financial Condition and Results of Operations" contained therein. Recently Issued Accounting Standards In February 2016, the FASB issued ASU 2016-02, Leases . The standard requires entities to record assets and obligations for contracts currently recognized as operating leases. In July 2018, the FASB issued ASU 2018-11, Leases (Topic 842): Targeted Improvements . The update provides an optional transition method of adoption that permits entities to initially apply the standard at the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. Under the optional transition method, comparative financial information and disclosures are not required. The update also provides transition practical expedients. The standard requires disclosures of the nature, maturity and value of an entity's lease liabilities and elections taken by the entity. In March 2019, the FASB issued ASU 2019-01, Leases (Topic 842): Codification Improvements , which, among other things, clarifies interim disclosure requirements in the year of ASU 2016-02 adoption. EQM adopted ASU 2016-02, ASU 2018-11 and ASU 2019-01 on January 1, 2019 using the optional transition method of adoption. EQM uses a lease accounting system to monitor its current population of lease contracts. EQM implemented processes and controls to review new lease contracts for appropriate accounting treatment in the context of the standards and to generate disclosures required under the standards. For the disclosures required by the standards, see Note 3 . In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses: Measurement of Credit Losses on Financial Instruments. The standard amends guidance on reporting credit losses for assets held at amortized cost basis and available for sale debt securities. For assets held at amortized cost basis, this standard eliminates the probable initial recognition threshold in current GAAP, and, in its place, requires an entity to recognize its current estimate of all expected credit losses. The amendments affect loans, debt securities, trade receivables, net investments in leases, off balance sheet credit exposures, reinsurance receivables, and any other financial assets not excluded from the scope of the standard that have the contractual right to receive cash. The standard will be effective for annual reporting periods beginning after December 15, 2019, including interim periods within that reporting period. EQM is currently evaluating the effect this standard will have on its financial statements and related disclosures. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement, Changes to the Disclosure Requirements for Fair Value Measurement , which makes a number of changes to the hierarchy associated with Level 1, 2 and 3 fair value measurements and the related disclosure requirements. This guidance is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted. EQM is currently evaluating the effect this standard will have on its financial statements and related disclosures but does not expect the adoption of this standard to have a material effect on its financial statements and related disclosures. In August 2018, the FASB issued ASU 2018-15, Intangibles—Goodwill and Other: Internal-Use Software , which aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). This guidance is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. EQM early-adopted the standard using the prospective method of adoption on January 1, 2019. Following the adoption of ASU 2018-15, EQM began capitalizing certain implementation costs related to cloud computing arrangements that are service contracts. The capitalized portion of these costs are included in the property, plant and equipment line on the consolidated balance sheets and will be amortized over the term of EQM's hosting arrangement, which has a fixed term of 7 years. For the three months ended March 31, 2019 , EQM did no t recognize any amortization expense related to implementation costs on its cloud computing arrangements as such assets were not in use. The costs will be included in the selling, general and administrative expense line on the accompanying statements of consolidated operations when recognized. In August 2018, the SEC adopted a final rule under SEC Release No. 33-10532, Disclosure Update and Simplification , that amends certain disclosure requirements that were redundant, duplicative, overlapping, outdated or superseded. The amendments also expanded the disclosure requirements on the analysis of stockholders' equity for interim financial statements, in that registrants must now analyze changes in stockholders’ equity, in the form of reconciliation, for the current and comparative year-to-date periods, with subtotals for each interim period. This final rule was effective on November 5, 2018 and EQM assessed the impact on its consolidated financial statements disclosures to be not significant. EQM adopted the final rule and began applying this disclosure change to its statement of consolidated equity in the first quarter of 2019.

Acquisitions and Mergers

Acquisitions and Mergers	3 Months Ended
	Mar. 31, 2019
Business Combinations [Abstract]
Acquisitions and Mergers	Acquisitions and Mergers Bolt-on Acquisition On March 13, 2019, EQM entered into a Purchase and Sale Agreement (the Purchase and Sale Agreement) with North Haven Infrastructure Partners II Buffalo Holdings, LLC (NHIP), an affiliate of Morgan Stanley Infrastructure Partners, pursuant to which EQM acquired from NHIP a 60% Class A interest in Eureka Midstream Holdings, LLC (Eureka Midstream) and a 100% interest in Hornet Midstream Holdings, LLC (Hornet Midstream) (collectively, the Bolt-on Acquisition) for total consideration of approximately $1.03 billion , composed of approximately $860 million in cash and approximately $170 million in assumed pro-rata debt, subject to certain adjustments set forth in the Purchase and Sale Agreement. Eureka Midstream owns a 190 -mile gathering header pipeline system in Ohio and West Virginia that services both dry Utica and wet Marcellus production. Hornet Midstream owns a 15 -mile, high-pressure gathering system in West Virginia that connects to the Eureka Midstream system. In connection with the entry into the Purchase and Sale Agreement, EQM deposited $50.0 million with an escrow agent, which is presented in restricted cash on the consolidated balance sheet as of March 31, 2019 . The deposit was credited towards the purchase price at the close of the acquisition. The Bolt-on Acquisition closed on April 10, 2019 and was funded through the Private Placement (as defined herein) of Series A Perpetual Convertible Preferred Units representing limited partner interests in EQM that closed concurrently with the Bolt-on Acquisition. See Note 4 for further information on the Private Placement. As of the closing of the Bolt-on Acquisition, Eureka Midstream, LLC (Eureka), a wholly owned subsidiary of Eureka Midstream, had a $400 million credit facility, which is available for general business purposes, including financing maintenance and expansion capital expenditures related to the Eureka system and providing working capital for Eureka’s operations. Shared Assets Transaction On March 31, 2019, EQM entered into an Assignment and Bill of Sale (the Assignment and Bill of Sale) with Equitrans Midstream pursuant to which EQM acquired certain assets and assumed certain leases that primarily support EQM’s operations for aggregate cash purchase price of $49.7 million (the initial purchase price), which reflected the net book value of in-service assets and expenditures made for assets not yet in-service and is subject to certain adjustments (collectively, the Shared Assets Transaction). Pursuant to the Assignment and Bill of Sale, EQM may assume an additional facilities lease, and may acquire certain additional assets from Equitrans Midstream for additional cash consideration reflecting the net book value of in-service assets and expenditures made with respect to assets not yet in-service. The initial purchase price was funded utilizing EQM’s $3 billion Facility (defined in Note 9 ). Prior to the Shared Assets Transaction, EQM made quarterly payments to Equitrans Midstream based on fees allocated from Equitrans Midstream for use of in-service assets transferred to EQM in the transaction. In connection with the entry into the Assignment and Bill of Sale, that certain Omnibus Agreement among Equitrans Midstream, EQM and the New EQM General Partner (as successor to the Former EQM General Partner) was amended and restated in order to, among other things, govern Equitrans Midstream’s use of the acquired assets following their conveyance to EQM and provide for reimbursement of EQM by Equitrans Midstream for expenses incurred by EQM in connection with such use. EQM-RMP Merger On April 25, 2018, EQM entered into an Agreement and Plan of Merger (the Merger Agreement) with RMP, Rice Midstream Management LLC, the general partner of RMP (the RMP General Partner), the Former EQM General Partner, EQM Acquisition Sub, LLC, a wholly-owned subsidiary of EQM (Merger Sub), EQM GP Acquisition Sub, LLC, a wholly-owned subsidiary of EQM (GP Merger Sub), and, solely for certain limited purposes set forth therein, EQT. Pursuant to the Merger Agreement, on July 23, 2018, Merger Sub and GP Merger Sub merged with and into RMP and the RMP General Partner, respectively, with RMP and the RMP General Partner surviving as wholly-owned subsidiaries of EQM. Pursuant to the Merger Agreement, each RMP common unit issued and outstanding immediately prior to the effective time of the EQM-RMP Merger was converted into the right to receive 0.3319 EQM common units (the Merger Consideration), the issued and outstanding IDRs of RMP were canceled and each outstanding award of phantom units in respect of RMP common units fully vested and converted into the right to receive the Merger Consideration, less applicable tax withholding, in respect of each RMP common unit subject thereto. The aggregate Merger Consideration consisted of approximately 34 million EQM common units of which 9,544,530 EQM common units were received by an indirect wholly-owned subsidiary of EQT. As a result of the EQM-RMP Merger , RMP's common units are no longer publicly traded. Drop-Down Transaction On April 25, 2018, EQT, Rice Midstream Holdings LLC (Rice Midstream Holdings), a wholly-owned subsidiary of EQT, EQM and EQM Gathering Holdings, LLC (EQM Gathering), a wholly-owned subsidiary of EQM, entered into a Contribution and Sale Agreement pursuant to which EQM Gathering acquired from EQT all of EQT's interests in EQM Olympus, Strike Force and EQM WV in exchange for an aggregate of 5,889,282 EQM common units and aggregate cash consideration of approximately $1.15 billion . EQM Olympus owns a natural gas gathering system that gathers gas from wells located primarily in Belmont County, Ohio. Strike Force owns a 75% limited liability company interest in Strike Force Midstream LLC (Strike Force Midstream). The Drop-Down Transaction closed on May 22, 2018 with an effective date of May 1, 2018 . As a result of the recast associated with the EQM-RMP Merger and the Drop-Down Transaction, EQM recognized approximately $1,384.9 million of goodwill, all of which was allocated to two reporting units within the Gathering segment. The goodwill value was based on a valuation performed by EQT as of November 13, 2017 with regard to the Rice Merger. EQT recorded goodwill as the excess of the estimated enterprise value of RMP, EQM Olympus, Strike Force and EQM WV over the sum of the fair value amounts allocated to the assets and liabilities of RMP, EQM Olympus, Strike Force and EQM WV. Goodwill was attributed to additional growth opportunities, synergies and operating leverage within the Gathering segment. Prior to the recast, EQM had no goodwill. Following EQT's initial valuation, certain estimates used in the purchase price allocation were updated. The net impact of these measurement period adjustments increased goodwill by approximately $0.9 million . The purchase price allocation was finalized and the measurement period adjustments were recorded as current period adjustments. The following table summarizes the allocation of the fair value of the assets and liabilities of RMP, EQM Olympus, Strike Force and EQM WV as of November 13, 2017 through pushdown accounting from EQT, as well as certain measurement period adjustments made subsequent to EQT's initial valuation. Goodwill and Purchase Price Allocation (Thousands) Estimated fair value of RMP, EQM Olympus, Strike Force (a) and EQM WV $ 4,014,984 Estimated Fair Value of Assets Acquired and Liabilities Assumed: Current assets (b) 132,459 Intangible assets (c) 623,200 Property and equipment, net (d) 2,265,900 Other non-current assets 118 Current liabilities (b) (117,124 ) RMP $850 Million Facility (e) (266,000 ) Other non-current liabilities (e) (9,323 ) Total estimated fair value of assets acquired and liabilities assumed 2,629,230 Goodwill as of November 13, 2017 (f) 1,385,754 Impairment of goodwill (g) 261,941 Goodwill as of December 31, 2018 $ 1,123,813 (a) Includes the estimated fair value attributable to noncontrolling interest of $166 million . (b) The fair value of current assets and current liabilities were assumed to approximate their carrying values. (c) The identifiable intangible assets for customer relationships were estimated by applying a discounted cash flow approach which was adjusted for customer attrition assumptions and projected market conditions. (d) The estimated fair value of long-lived property and equipment were determined utilizing estimated replacement cost adjusted for a usage or obsolescence factor. (e) The estimated fair value of long-term liabilities was determined utilizing observable market inputs where available or estimated based on their then current carrying values. (f) Reflected the value of perceived growth opportunities, synergies and operating leverage anticipated through the acquisition and ownership of the acquired gathering assets as of November 13, 2017. (g) During its annual goodwill assessment for the year ended December 31, 2018, EQM determined that carrying value of the RMP PA Gas Gathering reporting unit, which comprises the Pennsylvania gathering assets acquired in the Rice Merger, was greater than its fair value. As a result, EQM recognized an impairment to goodwill of approximately $261.9 million . The Gulfport Transaction On May 1, 2018, pursuant to the Purchase and Sale Agreement dated April 25, 2018, by and among EQM, EQM Gathering, Gulfport Energy Corporation (Gulfport) and an affiliate of Gulfport, EQM Gathering acquired the remaining 25% limited liability company interest in Strike Force Midstream not owned by Strike Force for $175 million (the Gulfport Transaction). As a result, EQM owned 100% of Strike Force Midstream effective as of May 1, 2018. RMP and the entities part of the Drop-Down Transaction were businesses and the related acquisitions were transactions between entities under common control; therefore, EQM recorded the assets and liabilities of these entities at their carrying amounts to EQT on the date of the respective transactions. The difference between EQT's net carrying amount and the total consideration paid to EQT was recorded as a capital transaction with EQT, which resulted in a reduction in equity. This portion of the consideration was recorded in financing activities in the statements of consolidated cash flows. EQM recast its consolidated financial statements to retrospectively reflect the EQM-RMP Merger and the Drop-Down Transaction for the periods the acquired businesses were under the common control of EQT; however, the consolidated financial statements are not necessarily indicative of the results of operations that would have occurred if EQM had owned the acquired businesses during the periods reported.

Equity

Equity	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Equity	Equity The following table summarizes changes in EQM's common units and Class B units, both representing limited partner interests in EQM, and general partner units during the year ended December 31, 2018 and from January 1, 2019 through March 31, 2019 . Limited Partner Interests Common Units Class B Units General Partner Units Total Balance at January 1, 2018 80,581,758 — 1,443,015 82,024,773 Common units issued (1) 10,821 — — 10,821 Drop-Down Transaction consideration 5,889,282 — — 5,889,282 Common units issued in the EQM-RMP Merger 33,975,777 — — 33,975,777 Balance at December 31, 2018 120,457,638 — 1,443,015 121,900,653 Unit cancellation (8 ) — — (8 ) EQM IDR Transaction (2) 80,000,000 7,000,000 (1,443,015 ) 85,556,985 Balance at March 31, 2019 200,457,630 7,000,000 — 207,457,630 (1) Units issued upon the resignation of a member of the Board of Directors of EQM's general partner. (2) In exchange for the cancellation of the EQM IDRs, EQM issued 87,000,000 EQM common units (the Exchange Consideration) to the Former EQM General Partner. At the effective time of the EQM IDR Merger, (i) the Exchange Consideration held by the Former EQM General Partner was canceled, (ii) 80,000,000 EQM common units and 7,000,000 Class B units were issued on a pro rata basis to certain affiliates of Equitrans Midstream, and (iii) 21,811,643 EQM common units held by EQGP were canceled and 21,811,643 EQM common units were issued pro rata to certain affiliates of Equitrans midstream. On February 22, 2019, the EQM IDRs were exchanged and canceled in the EQM IDR Transaction. After giving effect to the EQM IDR Transaction, including the issuance of the Class B units, Equitrans Gathering Holdings, LLC (Equitrans Gathering Holdings), EQM GP Corporation (EQM GP Corp) and Equitrans Midstream Holdings, LLC (EMH), each a wholly-owned subsidiary of Equitrans Midstream, held 89,505,616 , 89,536 and 27,650,303 EQM common units, respectively, representing an aggregate 56.5% limited partner interest in EQM as of March 31, 2019 . Additionally, Equitrans Gathering Holdings, EQM GP Corp and EMH held 6,153,907 , 6,155 and 839,938 EQM Class B units, respectively, representing an aggregate 3.4% limited partner interest in EQM as of March 31, 2019 . Following completion of the EQM IDR Transaction and as of March 31, 2019, Equitrans Midstream owned, directly or indirectly, 117,245,455 EQM common units and 7,000,000 Class B units (collectively representing a 59.9% limited partner interest in EQM) and the entire non-economic general partner interest in EQM, while the public owned a 40.1% limited partner interest in EQM. Following the completion of the Private Placement (defined below), certain investors owned an aggregate of 24.6 million Series A Preferred Units (defined below) and, taking into account such Series A Preferred Units issued in the Private Placement on an as-converted basis, as of March 31, 2019 , Equitrans Midstream would have owned, directly or indirectly, a 53.5% limited partner interest in EQM, as well as the non-economic general partner interest in EQM. Class B Units As discussed above and in Note 1 , in February 2019, EQM issued 7,000,000 Class B units representing a new class of limited partner interests in EQM as partial consideration for the EQM IDR Transaction. The Class B units are substantially similar in all respects to EQM's common units, except that the Class B units are not entitled to receive distributions of available cash until the applicable Class B unit conversion date (or, if earlier, a change of control). The Class B units are divided into three tranches, with the first tranche of 2,500,000 Class B units becoming convertible at the holder’s option into EQM common units on April 1, 2021, the second tranche of 2,500,000 Class B units becoming convertible at the holder’s option into EQM common units on April 1, 2022, and the third tranche of 2,000,000 Class B units becoming convertible at the holder’s option on April 1, 2023 (each, a Class B unit conversion date). Additionally, the Class B units will become convertible at the holder’s option into EQM common units immediately before a change of control of EQM. After the applicable Class B unit conversion date (or, if earlier, a change of control), whether or not such Class B units have been converted into EQM common units, the Class B units will participate pro rata with the EQM common units in distributions of available cash. The holders of Class B units vote together with the holders of EQM common units as a single class, except that Class B units owned by the general partner of EQM and its affiliates are excluded from voting if EQM common units owned by such parties are excluded from voting. Holders of Class B units are entitled to vote as a separate class on any matter that adversely affects the rights or preferences of the Class B units in relation to other classes of EQM partnership interests in any material respect or as required by law. Series A Preferred Units On March 13, 2019, EQM entered into a Convertible Preferred Unit Purchase Agreement (inclusive of certain Joinder Agreements entered into on March 18, 2019, the Preferred Unit Purchase Agreement) with certain investors to issue and sell in a private placement (the Private Placement) an aggregate of 24,605,291 Series A Perpetual Convertible Preferred Units (Series A Preferred Units) representing limited partner interests in EQM for a cash purchase price of $48.77 per Series A Preferred Unit, resulting in total gross proceeds of approximately $1.2 billion . The net proceeds from the Private Placement were used in part to fund the purchase price in the Bolt-on Acquisition and to pay certain fees and expenses related to the Bolt-on Acquisition, and the remainder is expected to be used for general partnership purposes. The Private Placement closed concurrently with the closing of the Bolt-on Acquisition on April 10, 2019 . The Series A Preferred Units rank senior to all common units and Class B units representing limited partner interests in EQM with respect to distribution rights and rights upon liquidation. The Series A Preferred Units will vote on an as-converted basis with the EQM common units and Class B units and will have certain other class voting rights with respect to any amendment to EQM's partnership agreement or its certificate of limited partnership that would be adverse (other than in a de minimis manner) to any of the rights, preferences or privileges of the Series A Preferred Units. The holders of the Series A Preferred Units are entitled to receive cumulative quarterly distributions at a rate of $1.0364 per Series A Preferred Unit for the first twenty distribution periods, and thereafter the quarterly distributions on the Series A Preferred Units will be an amount per Series A Preferred Unit for such quarter equal to (i) the Series A Preferred Unit purchase price of $48.77 per such unit, multiplied by (ii) a percentage equal to the sum of (A) the greater of (x) the 3-month LIBOR as of the second London banking day prior to the beginning of the applicable quarter and (y) 2.59% , and (B) 6.90% , multiplied by (iii) 25% . EQM will not be entitled to pay any distributions on any junior securities, including any EQM common units, prior to paying the quarterly distributions payable to the holders of Series A Preferred Units, including any previously accrued and unpaid distributions. Each holder of the Series A Preferred Units may elect to convert all or any portion of the Series A Preferred Units owned by it into EQM common units initially on a one-for-one basis, subject to customary anti-dilution adjustments and an adjustment for any distributions that have accrued but not been paid when due and partial period distributions, at any time (but not more often than once per fiscal quarter) after April 10, 2021 (or earlier liquidation, dissolution or winding up of EQM), provided that any conversion is for at least $30 million (calculated based on the closing price of the common units on the trading day preceding notice of conversion) or such lesser amount if such conversion relates to all of a holder’s remaining Series A Preferred Units. EQM may elect to convert all or any portion of the Series A Preferred Units into EQM common units at any time (but not more often than once per quarter) after April 10, 2021 if (i) the common units are listed for, or admitted to, trading on a national securities exchange, (ii) the closing price per common unit on the national securities exchange on which the common units are listed for, or admitted to, trading exceeds 140% of the Series A Preferred Unit purchase price of $48.77 per such unit for the 20 consecutive trading days immediately preceding notice of the conversion, (iii) the average daily trading volume of the common units on the national securities exchange on which the common units are listed for, or admitted to, trading exceeds 500,000 common units for the 20 consecutive trading days immediately preceding notice of the conversion, (iv) EQM has an effective registration statement on file with the SEC covering resales of the common units to be received by such holders upon any such conversion and (v) EQM has paid all accrued quarterly distributions in cash to the holders. Net Income per Limited Partner Unit and Cash Distributions Net Income per Limited Partner Unit. Net income per limited partner unit is calculated utilizing the two-class method by dividing the limited partner interest in net income by the weighted average number of limited partner units outstanding during the period. The two-class method uses an earnings allocation method under which earnings per limited partner unit are calculated for each class of common unit and any participating security considering all dividends declared and participation rights in undistributed earnings as if all earnings had been distributed during the period. Diluted net income per limited partner unit reflects the potential dilution that could occur if securities or agreements to issue common units were exercised, settled or converted into EQM common units. EQM uses the treasury stock method to compute potential common units from phantom units granted to independent and non-employee directors and the if-converted method to compute potential common units related to the conversion of Class B units. For diluted earnings per unit, EQM uses the more dilutive of the if-converted method or the two-class method. The phantom units granted to the independent and non-employee directors of EQM's general partner will be paid in common units on a director’s termination of service on the Board of Directors of EQM's general partner. The weighted average phantom unit awards included in the calculation of basic weighted average limited partner units outstanding were 21,908 and 22,748 for the three months ended March 31, 2019 and 2018 , respectively. 7,000,000 Class B units were included in the calculation of diluted weighted average limited partner units outstanding for the three months ended March 31, 2019 based upon the application of the if-converted method. As a result of the EQM IDR Transaction, EQM’s common unitholders are entitled to all distributions until the Class B units are converted to common units (other than distributions in respect of the Series A Preferred Units). Class B unitholders have no rights to distributions until they are converted into common units. Accordingly, for all periods prior to such conversions, the Class B units are not considered participating securities under the two-class method. For the three months ended March 31, 2019, net income attributable to EQM was fully allocated to EQM’s common unitholders. For the three months ended March 31, 2018, EQM's net income was allocated to the general partner and limited partners in accordance with their respective ownership percentages. Any common units issued during the period are included on a monthly weighted-average basis for the periods in which they were outstanding. The following table presents EQM's calculation of net income per limited partner unit for common and Class B limited partner units. Three Months Ended 2019 2018 (1) (Thousands, except per unit data) Net income attributable to EQM $ 251,931 $ 260,350 Less pre-acquisition net income allocated to parent — (83,132 ) Less general partner interest in net income – general partner units — (3,117 ) Less general partner interest in net income – IDRs — (44,164 ) Limited partner interest in net income $ 251,931 $ 129,937 Net income allocable to common units $ 251,931 $ 129,937 Net income allocable to Class B units $ — $ — Weighted average limited partner common units outstanding - basic 154,259 80,607 Weighted average limited partner common units outstanding - diluted (2) 161,259 80,607 Net income per limited partner common unit - basic $ 1.63 $ 1.61 Net income per limited partner common unit - diluted $ 1.56 $ 1.61 (1) Net income attributable to the Drop-Down Transaction and the EQM-RMP Merger for the periods prior to May 1, 2018 and July 23, 2018, respectively, was not allocated to the limited partners for purposes of calculating net income per limited partner unit as these pre-acquisition amounts were not available to the EQM unitholders. (2) Includes 7,000,000 Class B units accounted for under the if-converted method as if the units were outstanding for the entire period. Class B units are not a participating security as they do not participate in distributions. EQM Distributions. On April 23, 2019 , the Board of Directors of EQM's general partner declared a cash distribution to EQM's unitholders for the first quarter of 2019 of $1.145 per common unit. The cash distribution will be paid on May 14, 2019 to unitholders of record at the close of business on May 3, 2019 . Based on the EQM common units outstanding on April 30, 2019 , cash distributions to Equitrans Midstream will be approximately $134.2 million related to its limited partner interest in EQM.

Leases

Leases	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Leases	Leases As discussed in Note 1 , EQM adopted ASU 2016-02, ASU 2018-11 and ASU 2019-01 on January 1, 2019 (the Adoption Date) using the optional transition method of adoption. EQM elected a package of practical expedients that allows an entity to not reassess (i) whether a contract is or contains a lease, (ii) lease classification and (iii) initial direct costs. In addition, EQM elected the following practical expedients: (i) to not reassess certain land easements, (ii) to not apply the recognition requirements under the standard to short-term leases and (iii) to combine and account for lease and nonlease contract components as a lease, which requires the capitalization of fixed nonlease payments on the Adoption Date or lease effective date and the recognition of variable nonlease payments as variable lease expense. Nonlease payments include payments for property taxes and other operating and maintenance expenses incurred by the lessor but payable by EQM in connection with the leasing arrangement. On the Adoption Date, EQM recorded on its consolidated balance sheet an operating lease right-of-use asset and a corresponding operating lease liability of $2.3 million , reflecting the present value of future lease payments on EQM's facility and compressor lease contracts. The discount rate used to determine present value, referred to as the incremental borrowing rate, was based on the rate of interest that EQM estimated it would have to pay to borrow (on a collateralized-basis over a similar term) an amount equal to the lease payments in a similar economic environment as of the Adoption Date. EQM is required to reassess the incremental borrowing rate for any new and modified lease contracts as of the contract effective date. Adoption of the standard did not require an adjustment to the opening balance of retained earnings. As of the Adoption Date and March 31, 2019 , EQM had no lease contracts classified as financing leases and was neither a lessor nor party to a subleasing arrangement. As discussed in Note 2 , on March 31, 2019, Equitrans Midstream assigned to EQM two lease agreements that support EQM operations (the Shared Leases Assignment), one of which provides rights to a facility and the other to a compressor station. As a result of the Shared Leases Assignment, EQM recorded $33.0 million of right-of-use assets and corresponding operating lease liabilities. The following table summarizes operating lease cost for the three months ended March 31, 2019 . Three Months Ended March 31, 2019 (Thousands) Operating lease cost $ 1,297 Short-term lease cost 368 Variable lease cost 8 Total lease cost $ 1,673 Operating lease expense related to EQM's compressor lease contracts and facility lease contracts is reported in operating and maintenance expense and selling, general and administrative expense, respectively, on EQM's statement of consolidated operations. The current and noncurrent portions of the operating lease right-of-use assets are reported in other current assets and other assets, respectively, and the current and noncurrent portions of the operating lease liabilities are reported in accrued liabilities and regulatory and other long-term liabilities, respectively. As of March 31, 2019 , the operating lease right-of-use assets and operating lease liabilities had balances of $34.8 million and $34.9 million , respectively, of which $0.3 million and $2.8 million , respectively, were classified as current. As of March 31, 2019 , the weighted average remaining lease term was 11 years and the weighted average discount rate was 6.0% . Schedule of Operating Lease Liability Maturities. The following table summarizes undiscounted cash flows owed by EQM to lessors pursuant to contractual agreements in effect as of March 31, 2019 and related imputed interest. The majority of EQM's lease agreements have multiple renewal periods at EQM's option; however, because none of the renewal periods are reasonably assured to be exercised, the associated operating lease payments have not been included in the table below. March 31, 2019 (Thousands) 2019 $ 3,702 2020 4,218 2021 4,070 2022 4,117 2023 3,841 2024 3,889 Thereafter 24,729 Total 48,566 Less: imputed interest 13,671 Present value of operating lease liability $ 34,895

Financial Information by Busine

Financial Information by Business Segment	3 Months Ended
	Mar. 31, 2019
Segment Reporting [Abstract]
Financial Information by Business Segment	Financial Information by Business Segment EQM reports its operations in three segments that reflect its three lines of business of Gathering, Transmission and Water. Gathering includes EQM's high-pressure gathering lines and FERC-regulated low-pressure gathering line; Transmission includes EQM's FERC-regulated interstate pipeline and storage system; and Water consists of EQM's water pipelines, impoundment facilities, pumping stations, take point facilities and measurement facilities. Three Months Ended 2019 2018 (Thousands) Revenues from external customers (including related parties): Gathering $ 261,881 $ 237,390 Transmission 109,859 106,934 Water 18,042 26,702 Total operating revenues $ 389,782 $ 371,026 Operating income: Gathering $ 182,078 $ 171,035 Transmission 84,750 79,451 Water 1,186 15,312 Total operating income $ 268,014 $ 265,798 Reconciliation of operating income to net income: Equity income (a) 31,063 8,811 Other income 2,210 904 Net interest expense 49,356 12,670 Net income $ 251,931 $ 262,843 (a) Equity income is included in the Transmission segment. March 31, December 31, (Thousands) Segment assets: Gathering $ 6,234,581 $ 6,011,654 Transmission (a) 3,243,578 3,066,659 Water 242,334 237,602 Total operating segments 9,720,493 9,315,915 Headquarters, including cash 168,092 140,206 Total assets $ 9,888,585 $ 9,456,121 (a) The equity investment in the MVP Joint Venture is included in the Transmission segment. Three Months Ended 2019 2018 (Thousands) Depreciation: Gathering $ 28,116 $ 23,068 Transmission 12,533 12,441 Water 6,416 5,771 Total $ 47,065 $ 41,280 Expenditures for segment assets: Gathering (1) $ 207,717 $ 134,138 Transmission 18,762 18,929 Water 9,175 2,375 Total (2) $ 235,654 $ 155,442 (1) Includes approximately $49.7 million related to non-operating assets acquired from Equitrans Midstream in the Shared Assets Transaction that primarily support EQM's gathering activities. (2) EQM accrues capital expenditures when work has been completed but the associated bills have not yet been paid. These accrued amounts are excluded from capital expenditures in the statements of consolidated cash flows until they are paid. Accrued capital expenditures were approximately $137.8 million and $108.9 million at March 31, 2019 and December 31, 2018 , respectively. Accrued capital expenditures were approximately $75.5 million and $90.7 million at March 31, 2018 and December 31, 2017 , respectively.

Revenue from Contracts with Cus

Revenue from Contracts with Customers	3 Months Ended
	Mar. 31, 2019
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Customers	Revenue from Contracts with Customers For the three months ended March 31, 2019 and 2018 , all revenues recognized on EQM's statements of consolidated operations are from contracts with customers. As of March 31, 2019 and December 31, 2018 , all receivables recorded on EQM's consolidated balance sheets represent performance obligations that have been satisfied and for which an unconditional right to consideration exists. Summary of disaggregated revenues . The tables below provide disaggregated revenue information by business segment. Three Months Ended March 31, 2019 Gathering Transmission Water Total (Thousands) Firm reservation fee revenues $ 128,959 $ 99,224 $ — $ 228,183 Volumetric-based fee revenues 132,922 10,635 — 143,557 Water services revenues — — 18,042 18,042 Total operating revenues $ 261,881 $ 109,859 $ 18,042 $ 389,782 Three Months Ended March 31, 2018 Gathering Transmission Water Total (Thousands) Firm reservation fee revenues $ 109,933 $ 97,775 $ — $ 207,708 Volumetric-based fee revenues 127,457 9,159 — 136,616 Water services revenues — — 26,702 26,702 Total operating revenues $ 237,390 $ 106,934 $ 26,702 $ 371,026 Summary of Remaining Performance Obligations. The following table summarizes the transaction price allocated to EQM's remaining performance obligations under all contracts with firm reservation fees and MVCs as of March 31, 2019 . 2019 (a) 2020 2021 2022 2023 Thereafter Total (Thousands) Gathering firm reservation fees $ 353,984 $ 563,215 $ 573,214 $ 573,214 $ 573,214 $ 2,312,931 $ 4,949,772 Gathering revenues supported by MVCs 55,503 74,617 74,413 74,413 74,413 68,689 422,048 Transmission firm reservation fees 283,230 345,456 340,937 335,850 295,947 2,178,142 3,779,562 Total $ 692,717 $ 983,288 $ 988,564 $ 983,477 $ 943,574 $ 4,559,762 $ 9,151,382 (a) April 1, 2019 through December 31, 2019 Based on total projected contractual revenues, including projected contractual revenues from future capacity expected from expansion projects that are not yet fully constructed for which EQM has executed firm contracts, EQM's firm gathering contracts and firm transmission and storage contracts had weighted average remaining terms of approximately 11 years and 15 years, respectively, as of March 31, 2019 .

Related Party Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2019
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions Pursuant to an omnibus agreement (the ETRN Omnibus Agreement), Equitrans Midstream performs centralized corporate, general and administrative services for EQM. In exchange, EQM reimburses Equitrans Midstream for the expenses incurred by Equitrans Midstream in providing these services. In connection with the entry into the Assignment and Bill of Sale, the ETRN Omnibus Agreement was amended and restated, to, among other things, govern Equitrans Midstream's use, and payment for such use, of the acquired assets following their conveyance to EQM. Pursuant to a secondment agreement, employees of Equitrans Midstream and its affiliates may be seconded to EQM to provide operating and other services with respect to EQM's business under the direction, supervision and control of EQM. EQM reimburses Equitrans Midstream and its affiliates for the services provided by the seconded employees. The expenses for which EQM reimburses Equitrans Midstream and its affiliates may not necessarily reflect the actual expenses that EQM would incur on a stand-alone basis. EQM is unable to estimate what those expenses would be on a stand-alone basis. In connection with the Separation, Equitrans Midstream assumed certain obligations from EQT to indemnify and reimburse EQM. As of March 31, 2019 , EQT remained a related party following the Separation due to its 19.9% ownership interest in Equitrans Midstream. In the ordinary course of business, EQM engaged, and continues to engage, in transactions with EQT and its affiliates, including, but not limited to and as applicable, gathering agreements, transportation service and precedent agreements, storage agreements and water service agreements.

Investment in Unconsolidated En

Investment in Unconsolidated Entity	3 Months Ended
	Mar. 31, 2019
Equity Method Investments and Joint Ventures [Abstract]
Investment in Unconsolidated Entity	Investment in Unconsolidated Entity The MVP Joint Venture is constructing the Mountain Valley Pipeline (MVP), an estimated 300 -mile natural gas interstate pipeline that will span from northern West Virginia to southern Virginia. EQM is the operator of the MVP and owned a 45.5% interest in the MVP project as of March 31, 2019 . The MVP Joint Venture is a variable interest entity because it has insufficient equity to finance its activities during the construction stage of the project. EQM is not the primary beneficiary of the MVP Joint Venture because it does not have the power to direct the activities that most significantly affect the MVP Joint Venture's economic performance. Certain business decisions, such as decisions to make distributions of cash, require a greater than 66 2/3% ownership interest approval, and no one member owns more than a 66 2/3% interest. In April 2018, the MVP Joint Venture announced the MVP Southgate project, a proposed 70 -mile interstate pipeline that will extend from the MVP at Pittsylvania County, Virginia to new delivery points in Rockingham and Alamance Counties, North Carolina. As of March 31, 2019 , EQM had a 47.2% ownership interest in the MVP Southgate project and will operate the pipeline. Subject to approval by the FERC, the MVP Southgate project has a targeted in-service date of the fourth quarter of 2020. In March 2019 , the MVP Joint Venture issued a capital call notice for the funding of the MVP project to MVP Holdco, LLC (MVP Holdco), a direct, wholly-owned subsidiary of EQM, for $149.8 million , of which $25.5 million and $124.3 million is expected to be paid in May 2019 and June 2019 , respectively. In addition, in March 2019, the MVP Joint Venture issued a capital call notice for the funding of the MVP Southgate project to MVP Holdco for $6.6 million , of which $0.8 million was paid in April 2019, and $1.2 million and $4.6 million is expected to be paid in May 2019 and June 2019, respectively. The capital contribution payable and the corresponding increase to the investment balance are reflected on the consolidated balance sheet as of March 31, 2019 . The interests in MVP and MVP Southgate are equity method investments for accounting purposes because EQM has the ability to exercise significant influence over the MVP Joint Venture's operating and financial policies. Accordingly, EQM records adjustments to the investment balance for contributions to or distributions from the MVP Joint Venture and for EQM's pro-rata share of MVP Joint Venture earnings. Equity income, which is primarily related to EQM's pro-rata share of the MVP Joint Venture's AFUDC on the construction of the MVP, is reported in equity income in EQM's statements of consolidated operations. Pursuant to the MVP Joint Venture's limited liability company agreement, EQM is obligated to issue a performance guarantee in favor of the MVP Joint Venture to provide performance assurances of MVP Holdco's obligations to fund its proportionate share of the construction budget for the MVP project. In January 2019, EQM issued a performance guarantee in an amount equal to 33% of EQM's proportionate share of the construction budget for the MVP project, which was $261 million at the time of issuance. The amount of the performance guarantee will decrease based on the capital contributions made by MVP Holdco to the MVP Joint Venture. As of March 31, 2019 , the performance guarantee remained at $261 million . In addition, in February 2019, EQM issued a performance guarantee of $14 million in favor of the MVP Joint Venture for the MVP Southgate project. Upon the FERC's initial release to begin construction of the MVP Southgate project, EQM's current MVP Southgate performance guarantee will be terminated, and EQM will be obligated to issue a new guarantee in an amount equal to 33% of EQM's proportionate share of the remaining capital obligations for the MVP Southgate project. As of March 31, 2019 , EQM's maximum financial statement exposure related to the MVP Joint Venture was approximately $1,792 million , which consists of the investment in unconsolidated entity balance on the consolidated balance sheet as of March 31, 2019 and amounts that could have become due under EQM's performance guarantees as of that date. The following tables summarize the unaudited condensed financial statements of the MVP Joint Venture. Condensed Consolidated Balance Sheets March 31, December 31, (Thousands) Current assets $ 696,893 $ 687,657 Non-current assets 3,526,691 3,223,220 Total assets $ 4,223,584 $ 3,910,877 Current liabilities $ 571,907 $ 617,355 Non-current liabilities 2,192 — Equity 3,649,485 3,293,522 Total liabilities and equity $ 4,223,584 $ 3,910,877 Condensed Statements of Consolidated Operations Three Months Ended 2019 2018 (Thousands) Environmental remediation reserve $ (2,192 ) $ — Other income 2,913 534 Net interest income 20,235 5,649 AFUDC - equity 47,216 13,182 Net income $ 68,172 $ 19,365

Debt

Debt	3 Months Ended
	Mar. 31, 2019
Long-term Debt, Current and Noncurrent [Abstract]
Debt	Debt $3 Billion Facility. On October 31, 2018, EQM amended and restated its credit facility to increase the borrowing capacity from $1 billion to $3 billion and extend the term to October 2023 (the $3 Billion Facility). The $3 Billion Facility is available for general partnership purposes, including to purchase assets, and to fund working capital requirements and capital expenditures, pay distributions and repurchase units. Subject to satisfaction of certain conditions, the $3 Billion Facility has an accordion feature that allows EQM to increase the available borrowings under the facility by up to an additional $750 million . The $3 Billion Facility has a sublimit of up to $250 million for same-day swing line advances and a sublimit of up to $400 million for letters of credit. In addition, EQM has the ability to request that one or more lenders make available term loans under the $3 Billion Facility, subject to the satisfaction of certain conditions. Such term loans would be secured by cash and qualifying investment grade securities. EQM's obligations under the revolving portion of the $3 Billion Facility are unsecured. EQM's $3 Billion Facility contains negative covenants that, among other things, limit restricted payments, the incurrence of debt, dispositions, mergers and fundamental changes, and transactions with affiliates. In addition, the $3 billion Facility contains events of default such as insolvency, nonpayment of scheduled principal or interest obligations, change of control and cross-default related to the acceleration or default of certain other financial obligations. Under the $3 Billion Facility, EQM is required to maintain a consolidated leverage ratio of not more than 5.00 to 1.00 (or not more than 5.50 to 1.00 for certain measurement periods following the consummation of certain acquisitions). As of March 31, 2019 , EQM had approximately $1.1 billion of borrowings outstanding and $1 million of letters of credit outstanding under the $3 Billion Facility. As of December 31, 2018 , EQM had approximately $625 million of borrowings outstanding and $1 million of letters of credit outstanding under the $3 Billion Facility. During the three months ended March 31, 2019 and 2018, the maximum amount of EQM's outstanding borrowings under the $3 Billion Facility at any time was $1.1 billion and $420 million , respectively, and the average daily balance was approximately $942 million and $301 million , respectively. EQM incurred interest at weighted average annual interest rates of approximately 3.9% and 3.0% for the three months ended March 31, 2019 and 2018, respectively. EQM Term Loan Facility . On April 25, 2018, EQM entered into a $2.5 billion unsecured multi-draw 364 -day term loan facility with a syndicate of lenders (the EQM Term Loan Facility). The EQM Term Loan Facility was used to fund the cash consideration for the Drop-Down Transaction , to repay borrowings under EQM's then-existing revolving credit facility and for other general partnership purposes. In connection with EQM's issuance of the 2018 Senior Notes (defined below), on June 25, 2018, the balance outstanding under the EQM Term Loan Facility was repaid and the EQM Term Loan Facility was terminated. As a result of the termination, EQM expensed $3 million of deferred issuance costs. From April 25, 2018 through June 25, 2018, the maximum amount of EQM's outstanding borrowings under the EQM Term Loan Facility at any time was $1,825 million and the average daily balance was approximately $1,231 million . EQM incurred interest at a weighted average annual interest rate of approximately 3.3% for the period from April 25, 2018 through June 25, 2018. RMP $850 Million Facility. RM Operating LLC (formerly Rice Midstream OpCo LLC), a wholly-owned subsidiary of RMP, had an $850 million credit facility (the RMP $850 million Facility). In connection with the completion of the EQM-RMP Merger, on July 23, 2018, EQM repaid the approximately $260 million of borrowings outstanding under the RMP $850 Million Facility and the RMP $850 Million Facility was terminated. The RMP $850 Million Facility was available for general partnership purposes, including to purchase assets, and to fund working capital requirements and capital expenditures, pay distributions and repurchase units. The RMP $850 Million Facility was secured by mortgages and other security interests on substantially all of RMP's properties and was guaranteed by RMP and its restricted subsidiaries. During the three months ended March 31, 2018, the maximum outstanding borrowings were $336 million , the average daily balance was approximately $308 million and the weighted average annual interest rate for the period was approximately 3.6% . EQM 4.125% and 4.00% Senior Notes. In the fourth quarter of 2016, EQM issued $500 million aggregate principal amount of 4.125% senior notes due December 2026 (the 4.125% Senior Notes). EQM used the net proceeds from the offering to repay the then outstanding borrowings under a predecessor to the $3 billion Facility and for general partnership purposes. In the third quarter of 2014, EQM issued $500 million aggregate principal amount of 4.00% senior notes due August 2024 (the 4.00% Senior Notes). EQM used the net proceeds from the offering to repay the outstanding borrowings under a predecessor to the $3 billion Facility and for general partnership purposes. Both the 4.125% Senior Notes and the 4.00% Senior Notes contain covenants that limit EQM's ability to, among other things, incur certain liens securing indebtedness, engage in certain sale and leaseback transactions and enter into certain consolidations, mergers, conveyances, transfers or leases of all or substantially all of EQM's assets. 2018 Senior Notes. During the second quarter of 2018, EQM issued 4.75% senior notes due July 2023 in the aggregate principal amount of $1.1 billion , 5.50% senior notes due July 2028 in the aggregate principal amount of $850 million and 6.50% senior notes due July 2048 in the aggregate principal amount of $550 million (collectively, the 2018 Senior Notes). EQM received net proceeds from the offering of approximately $2,465.8 million , inclusive of a discount of $11.8 million and estimated debt issuance costs of $22.4 million . The net proceeds were used to repay the balances outstanding under the EQM Term Loan Facility and the RMP $850 Million Facility, and the remainder was used for general partnership purposes. The 2018 Senior Notes were issued pursuant to new supplemental indentures to EQM's existing indenture dated August 1, 2014. The 2018 Senior Notes contain covenants that limit EQM's ability to, among other things, incur certain liens securing indebtedness, engage in certain sale and leaseback transactions, and enter into certain consolidations, mergers, conveyances, transfers or leases of all or substantially all of EQM's assets. As of March 31, 2019 , EQM was in compliance with all debt provisions and covenants.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The carrying values of cash and cash equivalents, accounts receivable, amounts due to/from related parties and accounts payable approximate fair value due to the short maturity of the instruments; as such, their fair values are Level 1 fair value measurements. The carrying value of the credit facility borrowings approximates fair value as the interest rates are based on prevailing market rates; this is considered a Level 1 fair value measurement. As EQM's senior notes are not actively traded, their fair values are estimated using an income approach model that applies a discount rate based on prevailing market rates for debt with similar remaining time-to-maturity and credit risk; as such, their fair values are Level 2 fair value measurements. As of March 31, 2019 and December 31, 2018 , the estimated fair value of EQM's senior notes was approximately $3,504 million and $3,425 million , respectively, and the carrying value of EQM's senior notes was approximately $3,458 million and $3,457 million , respectively. The fair value of the Preferred Interest is a Level 3 fair value measurement and is estimated using an income approach model that applies a market-based discount rate. As of March 31, 2019 and December 31, 2018 , the estimated fair value of the Preferred Interest was approximately $124 million and $122 million , respectively, and the carrying value of the Preferred Interest was approximately $114 million and $115 million , respectively.

Net Income per Limited Partner

Net Income per Limited Partner Unit and Cash Distributions	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Net Income per Limited Partner Unit and Cash Distributions	Equity The following table summarizes changes in EQM's common units and Class B units, both representing limited partner interests in EQM, and general partner units during the year ended December 31, 2018 and from January 1, 2019 through March 31, 2019 . Limited Partner Interests Common Units Class B Units General Partner Units Total Balance at January 1, 2018 80,581,758 — 1,443,015 82,024,773 Common units issued (1) 10,821 — — 10,821 Drop-Down Transaction consideration 5,889,282 — — 5,889,282 Common units issued in the EQM-RMP Merger 33,975,777 — — 33,975,777 Balance at December 31, 2018 120,457,638 — 1,443,015 121,900,653 Unit cancellation (8 ) — — (8 ) EQM IDR Transaction (2) 80,000,000 7,000,000 (1,443,015 ) 85,556,985 Balance at March 31, 2019 200,457,630 7,000,000 — 207,457,630 (1) Units issued upon the resignation of a member of the Board of Directors of EQM's general partner. (2) In exchange for the cancellation of the EQM IDRs, EQM issued 87,000,000 EQM common units (the Exchange Consideration) to the Former EQM General Partner. At the effective time of the EQM IDR Merger, (i) the Exchange Consideration held by the Former EQM General Partner was canceled, (ii) 80,000,000 EQM common units and 7,000,000 Class B units were issued on a pro rata basis to certain affiliates of Equitrans Midstream, and (iii) 21,811,643 EQM common units held by EQGP were canceled and 21,811,643 EQM common units were issued pro rata to certain affiliates of Equitrans midstream. On February 22, 2019, the EQM IDRs were exchanged and canceled in the EQM IDR Transaction. After giving effect to the EQM IDR Transaction, including the issuance of the Class B units, Equitrans Gathering Holdings, LLC (Equitrans Gathering Holdings), EQM GP Corporation (EQM GP Corp) and Equitrans Midstream Holdings, LLC (EMH), each a wholly-owned subsidiary of Equitrans Midstream, held 89,505,616 , 89,536 and 27,650,303 EQM common units, respectively, representing an aggregate 56.5% limited partner interest in EQM as of March 31, 2019 . Additionally, Equitrans Gathering Holdings, EQM GP Corp and EMH held 6,153,907 , 6,155 and 839,938 EQM Class B units, respectively, representing an aggregate 3.4% limited partner interest in EQM as of March 31, 2019 . Following completion of the EQM IDR Transaction and as of March 31, 2019, Equitrans Midstream owned, directly or indirectly, 117,245,455 EQM common units and 7,000,000 Class B units (collectively representing a 59.9% limited partner interest in EQM) and the entire non-economic general partner interest in EQM, while the public owned a 40.1% limited partner interest in EQM. Following the completion of the Private Placement (defined below), certain investors owned an aggregate of 24.6 million Series A Preferred Units (defined below) and, taking into account such Series A Preferred Units issued in the Private Placement on an as-converted basis, as of March 31, 2019 , Equitrans Midstream would have owned, directly or indirectly, a 53.5% limited partner interest in EQM, as well as the non-economic general partner interest in EQM. Class B Units As discussed above and in Note 1 , in February 2019, EQM issued 7,000,000 Class B units representing a new class of limited partner interests in EQM as partial consideration for the EQM IDR Transaction. The Class B units are substantially similar in all respects to EQM's common units, except that the Class B units are not entitled to receive distributions of available cash until the applicable Class B unit conversion date (or, if earlier, a change of control). The Class B units are divided into three tranches, with the first tranche of 2,500,000 Class B units becoming convertible at the holder’s option into EQM common units on April 1, 2021, the second tranche of 2,500,000 Class B units becoming convertible at the holder’s option into EQM common units on April 1, 2022, and the third tranche of 2,000,000 Class B units becoming convertible at the holder’s option on April 1, 2023 (each, a Class B unit conversion date). Additionally, the Class B units will become convertible at the holder’s option into EQM common units immediately before a change of control of EQM. After the applicable Class B unit conversion date (or, if earlier, a change of control), whether or not such Class B units have been converted into EQM common units, the Class B units will participate pro rata with the EQM common units in distributions of available cash. The holders of Class B units vote together with the holders of EQM common units as a single class, except that Class B units owned by the general partner of EQM and its affiliates are excluded from voting if EQM common units owned by such parties are excluded from voting. Holders of Class B units are entitled to vote as a separate class on any matter that adversely affects the rights or preferences of the Class B units in relation to other classes of EQM partnership interests in any material respect or as required by law. Series A Preferred Units On March 13, 2019, EQM entered into a Convertible Preferred Unit Purchase Agreement (inclusive of certain Joinder Agreements entered into on March 18, 2019, the Preferred Unit Purchase Agreement) with certain investors to issue and sell in a private placement (the Private Placement) an aggregate of 24,605,291 Series A Perpetual Convertible Preferred Units (Series A Preferred Units) representing limited partner interests in EQM for a cash purchase price of $48.77 per Series A Preferred Unit, resulting in total gross proceeds of approximately $1.2 billion . The net proceeds from the Private Placement were used in part to fund the purchase price in the Bolt-on Acquisition and to pay certain fees and expenses related to the Bolt-on Acquisition, and the remainder is expected to be used for general partnership purposes. The Private Placement closed concurrently with the closing of the Bolt-on Acquisition on April 10, 2019 . The Series A Preferred Units rank senior to all common units and Class B units representing limited partner interests in EQM with respect to distribution rights and rights upon liquidation. The Series A Preferred Units will vote on an as-converted basis with the EQM common units and Class B units and will have certain other class voting rights with respect to any amendment to EQM's partnership agreement or its certificate of limited partnership that would be adverse (other than in a de minimis manner) to any of the rights, preferences or privileges of the Series A Preferred Units. The holders of the Series A Preferred Units are entitled to receive cumulative quarterly distributions at a rate of $1.0364 per Series A Preferred Unit for the first twenty distribution periods, and thereafter the quarterly distributions on the Series A Preferred Units will be an amount per Series A Preferred Unit for such quarter equal to (i) the Series A Preferred Unit purchase price of $48.77 per such unit, multiplied by (ii) a percentage equal to the sum of (A) the greater of (x) the 3-month LIBOR as of the second London banking day prior to the beginning of the applicable quarter and (y) 2.59% , and (B) 6.90% , multiplied by (iii) 25% . EQM will not be entitled to pay any distributions on any junior securities, including any EQM common units, prior to paying the quarterly distributions payable to the holders of Series A Preferred Units, including any previously accrued and unpaid distributions. Each holder of the Series A Preferred Units may elect to convert all or any portion of the Series A Preferred Units owned by it into EQM common units initially on a one-for-one basis, subject to customary anti-dilution adjustments and an adjustment for any distributions that have accrued but not been paid when due and partial period distributions, at any time (but not more often than once per fiscal quarter) after April 10, 2021 (or earlier liquidation, dissolution or winding up of EQM), provided that any conversion is for at least $30 million (calculated based on the closing price of the common units on the trading day preceding notice of conversion) or such lesser amount if such conversion relates to all of a holder’s remaining Series A Preferred Units. EQM may elect to convert all or any portion of the Series A Preferred Units into EQM common units at any time (but not more often than once per quarter) after April 10, 2021 if (i) the common units are listed for, or admitted to, trading on a national securities exchange, (ii) the closing price per common unit on the national securities exchange on which the common units are listed for, or admitted to, trading exceeds 140% of the Series A Preferred Unit purchase price of $48.77 per such unit for the 20 consecutive trading days immediately preceding notice of the conversion, (iii) the average daily trading volume of the common units on the national securities exchange on which the common units are listed for, or admitted to, trading exceeds 500,000 common units for the 20 consecutive trading days immediately preceding notice of the conversion, (iv) EQM has an effective registration statement on file with the SEC covering resales of the common units to be received by such holders upon any such conversion and (v) EQM has paid all accrued quarterly distributions in cash to the holders. Net Income per Limited Partner Unit and Cash Distributions Net Income per Limited Partner Unit. Net income per limited partner unit is calculated utilizing the two-class method by dividing the limited partner interest in net income by the weighted average number of limited partner units outstanding during the period. The two-class method uses an earnings allocation method under which earnings per limited partner unit are calculated for each class of common unit and any participating security considering all dividends declared and participation rights in undistributed earnings as if all earnings had been distributed during the period. Diluted net income per limited partner unit reflects the potential dilution that could occur if securities or agreements to issue common units were exercised, settled or converted into EQM common units. EQM uses the treasury stock method to compute potential common units from phantom units granted to independent and non-employee directors and the if-converted method to compute potential common units related to the conversion of Class B units. For diluted earnings per unit, EQM uses the more dilutive of the if-converted method or the two-class method. The phantom units granted to the independent and non-employee directors of EQM's general partner will be paid in common units on a director’s termination of service on the Board of Directors of EQM's general partner. The weighted average phantom unit awards included in the calculation of basic weighted average limited partner units outstanding were 21,908 and 22,748 for the three months ended March 31, 2019 and 2018 , respectively. 7,000,000 Class B units were included in the calculation of diluted weighted average limited partner units outstanding for the three months ended March 31, 2019 based upon the application of the if-converted method. As a result of the EQM IDR Transaction, EQM’s common unitholders are entitled to all distributions until the Class B units are converted to common units (other than distributions in respect of the Series A Preferred Units). Class B unitholders have no rights to distributions until they are converted into common units. Accordingly, for all periods prior to such conversions, the Class B units are not considered participating securities under the two-class method. For the three months ended March 31, 2019, net income attributable to EQM was fully allocated to EQM’s common unitholders. For the three months ended March 31, 2018, EQM's net income was allocated to the general partner and limited partners in accordance with their respective ownership percentages. Any common units issued during the period are included on a monthly weighted-average basis for the periods in which they were outstanding. The following table presents EQM's calculation of net income per limited partner unit for common and Class B limited partner units. Three Months Ended 2019 2018 (1) (Thousands, except per unit data) Net income attributable to EQM $ 251,931 $ 260,350 Less pre-acquisition net income allocated to parent — (83,132 ) Less general partner interest in net income – general partner units — (3,117 ) Less general partner interest in net income – IDRs — (44,164 ) Limited partner interest in net income $ 251,931 $ 129,937 Net income allocable to common units $ 251,931 $ 129,937 Net income allocable to Class B units $ — $ — Weighted average limited partner common units outstanding - basic 154,259 80,607 Weighted average limited partner common units outstanding - diluted (2) 161,259 80,607 Net income per limited partner common unit - basic $ 1.63 $ 1.61 Net income per limited partner common unit - diluted $ 1.56 $ 1.61 (1) Net income attributable to the Drop-Down Transaction and the EQM-RMP Merger for the periods prior to May 1, 2018 and July 23, 2018, respectively, was not allocated to the limited partners for purposes of calculating net income per limited partner unit as these pre-acquisition amounts were not available to the EQM unitholders. (2) Includes 7,000,000 Class B units accounted for under the if-converted method as if the units were outstanding for the entire period. Class B units are not a participating security as they do not participate in distributions. EQM Distributions. On April 23, 2019 , the Board of Directors of EQM's general partner declared a cash distribution to EQM's unitholders for the first quarter of 2019 of $1.145 per common unit. The cash distribution will be paid on May 14, 2019 to unitholders of record at the close of business on May 3, 2019 . Based on the EQM common units outstanding on April 30, 2019 , cash distributions to Equitrans Midstream will be approximately $134.2 million related to its limited partner interest in EQM.

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2019
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events See Notes 2 and 4 for a discussion of the Bolt-on Acquisition and the Private Placement, respectively, both of which closed on April 10, 2019.

Financial Statements (Policies)

Financial Statements (Policies)	3 Months Ended
	Mar. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Basis of Presentation	Organization and Basis of Presentation EQM is a growth-oriented Delaware limited partnership formed by EQT in January 2012. Prior to the completion of the EQM IDR Transaction (defined below), EQM Midstream Services, LLC was a direct, wholly-owned subsidiary of EQGP Holdings, LP (EQGP) and was the general partner of EQM (the Former EQM General Partner). Following the consummation of the EQM IDR Transaction, EQGP Services, LLC, a wholly-owned indirect subsidiary of Equitrans Midstream, became the general partner of EQM (the New EQM General Partner). References in these consolidated financial statements to Equitrans Midstream refer collectively to Equitrans Midstream Corporation and its consolidated subsidiaries. On February 21, 2018, EQT announced its plan to separate its midstream business, which was composed of the separately-operated natural gas gathering, transmission and storage and water services operations of EQT (collectively, the Midstream Business), from its upstream business, which was composed of the natural gas, oil and natural gas liquids development, production and sales and commercial operations of EQT (collectively, the Upstream Business) (the Separation). On November 12, 2018, the Separation was effected through a series of transactions that culminated in EQT's contribution of the Midstream Business to Equitrans Midstream. On February 22, 2019, Equitrans Midstream completed its previously announced simplification transaction pursuant to that certain Agreement and Plan of Merger, dated as of February 13, 2019 (the IDR Merger Agreement), by and among Equitrans Midstream, EQM, the Former EQM General Partner, EQGP, the New EQM General Partner, Equitrans Merger Sub, LP, a Delaware limited partnership (Merger Sub), and certain other parties thereto. Pursuant to the IDR Merger Agreement, on February 22, 2019, (i) Merger Sub merged with and into EQGP (the Merger) with EQGP continuing as the surviving limited partnership and a wholly-owned subsidiary of EQM following the Merger, and (ii) each of (a) the incentive distribution rights (IDRs) in EQM, (b) the economic portion of the general partner interest in EQM and (c) the issued and outstanding common units representing limited partner interests in EQGP were canceled, and, as consideration for such cancellation, certain affiliates of Equitrans Midstream received on a pro rata basis 80,000,000 newly-issued EQM common units and 7,000,000 newly-issued Class B units (Class B units), both representing limited partner interests in EQM, and the New EQM General Partner retained the non-economic general partner interest in EQM (the EQM IDR Transaction). Additionally as part of the EQM IDR Transaction, the 21,811,643 EQM common units held by EQGP were canceled and 21,811,643 EQM common units were issued pro rata to certain affiliates of Equitrans Midstream. Following the EQM IDR Transaction, Equitrans Midstream continued to hold investments in the entities conducting the Midstream Business, which, following the EQM IDR Transaction and as of March 31, 2019, represented a 59.9% limited partner interest and the non-economic general partner interest in EQM. See Note 4 for further information. The EQM IDR Transaction constituted an exchange of equity interests between entities under common control and not a transfer of a business. Therefore, the exchange resulted in a reclassification, as of February 22, 2019, of a $43.8 million deficit capital balance from the general partner line item to the common and Class B line items in EQM's consolidated balance sheets based on the respective limited partner ownership interests. The reclassification represented an allocation of the carrying value of the exchanged general partner interest. Prior to the EQM IDR Transaction, when distributions related to the general partner interest and IDRs were made, earnings equal to the amount of distributions were allocated to the general partner before the remaining earnings were allocated to the limited partner unitholders based on their respective ownership percentages. Subsequent to the EQM IDR Transaction, no earnings will be allocated to the general partner. The allocation of net income attributable to EQM for purposes of calculating net income per limited partner unit is described in Note 11 . EQM's consolidated financial statements have been retrospectively recast to include the pre-acquisition results of the Drop-Down Transaction and the EQM-RMP Merger because these transactions represented business combinations between entities under common control. The recast is for the period the acquired businesses were under the common control of EQT, which began on November 13, 2017 as a result of EQT's acquisition of Rice Energy Inc. (Rice) (the Rice Merger). EQM recorded the assets and liabilities acquired in the Drop-Down Transaction and the EQM-RMP Merger at their carrying amounts to EQT on the effective dates of the transactions. The consolidated financial statements are not necessarily indicative of the actual results of operations if EQM and the assets acquired in the Drop-Down Transaction and the EQM-RMP Merger had been operated together during the pre-acquisition periods. The accompanying unaudited consolidated financial statements have been prepared in accordance with GAAP for interim financial information and with the requirements of Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of management, these unaudited consolidated financial statements include all adjustments (consisting of only normal recurring adjustments, unless otherwise disclosed in this Form 10-Q) necessary for a fair presentation of the financial position of EQM as of March 31, 2019 and December 31, 2018 and the results of its operations, cash flows and equity for the three months ended March 31, 2019 and 2018 . The balance sheet at December 31, 2018 has been derived from the audited financial statements at that date but does not include all of the information and footnotes required by GAAP for complete financial statements. Due to the seasonal nature of EQM's utility customer contracts, the interim statements for the three months ended March 31, 2019 are not necessarily indicative of the results that may be expected for the year ending December 31, 2019 . EQM does not have any employees. Operational, management and other services for EQM are provided by the directors and officers of the New EQM General Partner and employees of Equitrans Midstream. For further information, refer to the consolidated financial statements and related footnotes for the year ended December 31, 2018, as well as "Management's Discussion and Analysis of Financial Condition and Results of Operations" contained therein.
Recently Issued Accounting Standards	Recently Issued Accounting Standards In February 2016, the FASB issued ASU 2016-02, Leases . The standard requires entities to record assets and obligations for contracts currently recognized as operating leases. In July 2018, the FASB issued ASU 2018-11, Leases (Topic 842): Targeted Improvements . The update provides an optional transition method of adoption that permits entities to initially apply the standard at the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. Under the optional transition method, comparative financial information and disclosures are not required. The update also provides transition practical expedients. The standard requires disclosures of the nature, maturity and value of an entity's lease liabilities and elections taken by the entity. In March 2019, the FASB issued ASU 2019-01, Leases (Topic 842): Codification Improvements , which, among other things, clarifies interim disclosure requirements in the year of ASU 2016-02 adoption. EQM adopted ASU 2016-02, ASU 2018-11 and ASU 2019-01 on January 1, 2019 using the optional transition method of adoption. EQM uses a lease accounting system to monitor its current population of lease contracts. EQM implemented processes and controls to review new lease contracts for appropriate accounting treatment in the context of the standards and to generate disclosures required under the standards. For the disclosures required by the standards, see Note 3 . In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses: Measurement of Credit Losses on Financial Instruments. The standard amends guidance on reporting credit losses for assets held at amortized cost basis and available for sale debt securities. For assets held at amortized cost basis, this standard eliminates the probable initial recognition threshold in current GAAP, and, in its place, requires an entity to recognize its current estimate of all expected credit losses. The amendments affect loans, debt securities, trade receivables, net investments in leases, off balance sheet credit exposures, reinsurance receivables, and any other financial assets not excluded from the scope of the standard that have the contractual right to receive cash. The standard will be effective for annual reporting periods beginning after December 15, 2019, including interim periods within that reporting period. EQM is currently evaluating the effect this standard will have on its financial statements and related disclosures. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement, Changes to the Disclosure Requirements for Fair Value Measurement , which makes a number of changes to the hierarchy associated with Level 1, 2 and 3 fair value measurements and the related disclosure requirements. This guidance is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted. EQM is currently evaluating the effect this standard will have on its financial statements and related disclosures but does not expect the adoption of this standard to have a material effect on its financial statements and related disclosures. In August 2018, the FASB issued ASU 2018-15, Intangibles—Goodwill and Other: Internal-Use Software , which aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). This guidance is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. EQM early-adopted the standard using the prospective method of adoption on January 1, 2019. Following the adoption of ASU 2018-15, EQM began capitalizing certain implementation costs related to cloud computing arrangements that are service contracts. The capitalized portion of these costs are included in the property, plant and equipment line on the consolidated balance sheets and will be amortized over the term of EQM's hosting arrangement, which has a fixed term of 7 years. For the three months ended March 31, 2019 , EQM did no t recognize any amortization expense related to implementation costs on its cloud computing arrangements as such assets were not in use. The costs will be included in the selling, general and administrative expense line on the accompanying statements of consolidated operations when recognized. In August 2018, the SEC adopted a final rule under SEC Release No. 33-10532, Disclosure Update and Simplification , that amends certain disclosure requirements that were redundant, duplicative, overlapping, outdated or superseded. The amendments also expanded the disclosure requirements on the analysis of stockholders' equity for interim financial statements, in that registrants must now analyze changes in stockholders’ equity, in the form of reconciliation, for the current and comparative year-to-date periods, with subtotals for each interim period. This final rule was effective on November 5, 2018 and EQM assessed the impact on its consolidated financial statements disclosures to be not significant. EQM adopted the final rule and began applying this disclosure change to its statement of consolidated equity in the first quarter of 2019.

Acquisitions and Mergers (Table

Acquisitions and Mergers (Tables)	3 Months Ended
	Mar. 31, 2019
Business Combinations [Abstract]
Schedule Fair Value of Assets Acquired and Liabilities Assumed	The following table summarizes the allocation of the fair value of the assets and liabilities of RMP, EQM Olympus, Strike Force and EQM WV as of November 13, 2017 through pushdown accounting from EQT, as well as certain measurement period adjustments made subsequent to EQT's initial valuation. Goodwill and Purchase Price Allocation (Thousands) Estimated fair value of RMP, EQM Olympus, Strike Force (a) and EQM WV $ 4,014,984 Estimated Fair Value of Assets Acquired and Liabilities Assumed: Current assets (b) 132,459 Intangible assets (c) 623,200 Property and equipment, net (d) 2,265,900 Other non-current assets 118 Current liabilities (b) (117,124 ) RMP $850 Million Facility (e) (266,000 ) Other non-current liabilities (e) (9,323 ) Total estimated fair value of assets acquired and liabilities assumed 2,629,230 Goodwill as of November 13, 2017 (f) 1,385,754 Impairment of goodwill (g) 261,941 Goodwill as of December 31, 2018 $ 1,123,813 (a) Includes the estimated fair value attributable to noncontrolling interest of $166 million . (b) The fair value of current assets and current liabilities were assumed to approximate their carrying values. (c) The identifiable intangible assets for customer relationships were estimated by applying a discounted cash flow approach which was adjusted for customer attrition assumptions and projected market conditions. (d) The estimated fair value of long-lived property and equipment were determined utilizing estimated replacement cost adjusted for a usage or obsolescence factor. (e) The estimated fair value of long-term liabilities was determined utilizing observable market inputs where available or estimated based on their then current carrying values. (f) Reflected the value of perceived growth opportunities, synergies and operating leverage anticipated through the acquisition and ownership of the acquired gathering assets as of November 13, 2017. (g) During its annual goodwill assessment for the year ended December 31, 2018, EQM determined that carrying value of the RMP PA Gas Gathering reporting unit, which comprises the Pennsylvania gathering assets acquired in the Rice Merger, was greater than its fair value. As a result, EQM recognized an impairment to goodwill of approximately $261.9 million .

Equity (Tables)

Equity (Tables)	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Summary of Units Issued	The following table summarizes changes in EQM's common units and Class B units, both representing limited partner interests in EQM, and general partner units during the year ended December 31, 2018 and from January 1, 2019 through March 31, 2019 . Limited Partner Interests Common Units Class B Units General Partner Units Total Balance at January 1, 2018 80,581,758 — 1,443,015 82,024,773 Common units issued (1) 10,821 — — 10,821 Drop-Down Transaction consideration 5,889,282 — — 5,889,282 Common units issued in the EQM-RMP Merger 33,975,777 — — 33,975,777 Balance at December 31, 2018 120,457,638 — 1,443,015 121,900,653 Unit cancellation (8 ) — — (8 ) EQM IDR Transaction (2) 80,000,000 7,000,000 (1,443,015 ) 85,556,985 Balance at March 31, 2019 200,457,630 7,000,000 — 207,457,630 (1) Units issued upon the resignation of a member of the Board of Directors of EQM's general partner. (2) In exchange for the cancellation of the EQM IDRs, EQM issued 87,000,000 EQM common units (the Exchange Consideration) to the Former EQM General Partner. At the effective time of the EQM IDR Merger, (i) the Exchange Consideration held by the Former EQM General Partner was canceled, (ii) 80,000,000 EQM common units and 7,000,000 Class B units were issued on a pro rata basis to certain affiliates of Equitrans Midstream, and (iii) 21,811,643 EQM common units held by EQGP were canceled and 21,811,643 EQM common units were issued pro rata to certain affiliates of Equitrans midstream.

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Schedule of Operating Lease Cost	The following table summarizes operating lease cost for the three months ended March 31, 2019 . Three Months Ended March 31, 2019 (Thousands) Operating lease cost $ 1,297 Short-term lease cost 368 Variable lease cost 8 Total lease cost $ 1,673
Schedule of Operating Lease Liability Maturities	The following table summarizes undiscounted cash flows owed by EQM to lessors pursuant to contractual agreements in effect as of March 31, 2019 and related imputed interest. The majority of EQM's lease agreements have multiple renewal periods at EQM's option; however, because none of the renewal periods are reasonably assured to be exercised, the associated operating lease payments have not been included in the table below. March 31, 2019 (Thousands) 2019 $ 3,702 2020 4,218 2021 4,070 2022 4,117 2023 3,841 2024 3,889 Thereafter 24,729 Total 48,566 Less: imputed interest 13,671 Present value of operating lease liability $ 34,895

Financial Information by Busi_2

Financial Information by Business Segment (Tables)	3 Months Ended
	Mar. 31, 2019
Segment Reporting [Abstract]
Schedule of Revenue from External Customers and Operating Income and Reconciliation to Net Income	Three Months Ended 2019 2018 (Thousands) Revenues from external customers (including related parties): Gathering $ 261,881 $ 237,390 Transmission 109,859 106,934 Water 18,042 26,702 Total operating revenues $ 389,782 $ 371,026 Operating income: Gathering $ 182,078 $ 171,035 Transmission 84,750 79,451 Water 1,186 15,312 Total operating income $ 268,014 $ 265,798 Reconciliation of operating income to net income: Equity income (a) 31,063 8,811 Other income 2,210 904 Net interest expense 49,356 12,670 Net income $ 251,931 $ 262,843 (a) Equity income is included in the Transmission segment.
Schedule of Segment Assets	March 31, December 31, (Thousands) Segment assets: Gathering $ 6,234,581 $ 6,011,654 Transmission (a) 3,243,578 3,066,659 Water 242,334 237,602 Total operating segments 9,720,493 9,315,915 Headquarters, including cash 168,092 140,206 Total assets $ 9,888,585 $ 9,456,121 (a) The equity investment in the MVP Joint Venture is included in the Transmission segment.
Schedule of Depreciation, Amortization, and Expenditures for Segment Assets	Three Months Ended 2019 2018 (Thousands) Depreciation: Gathering $ 28,116 $ 23,068 Transmission 12,533 12,441 Water 6,416 5,771 Total $ 47,065 $ 41,280 Expenditures for segment assets: Gathering (1) $ 207,717 $ 134,138 Transmission 18,762 18,929 Water 9,175 2,375 Total (2) $ 235,654 $ 155,442 (1) Includes approximately $49.7 million related to non-operating assets acquired from Equitrans Midstream in the Shared Assets Transaction that primarily support EQM's gathering activities. (2) EQM accrues capital expenditures when work has been completed but the associated bills have not yet been paid. These accrued amounts are excluded from capital expenditures in the statements of consolidated cash flows until they are paid. Accrued capital expenditures were approximately $137.8 million and $108.9 million at March 31, 2019 and December 31, 2018 , respectively. Accrued capital expenditures were approximately $75.5 million and $90.7 million at March 31, 2018 and December 31, 2017 , respectively.

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	3 Months Ended
	Mar. 31, 2019
Revenue from Contract with Customer [Abstract]
Schedule of Disaggregated Revenue Information, by Business Segment	The tables below provide disaggregated revenue information by business segment. Three Months Ended March 31, 2019 Gathering Transmission Water Total (Thousands) Firm reservation fee revenues $ 128,959 $ 99,224 $ — $ 228,183 Volumetric-based fee revenues 132,922 10,635 — 143,557 Water services revenues — — 18,042 18,042 Total operating revenues $ 261,881 $ 109,859 $ 18,042 $ 389,782 Three Months Ended March 31, 2018 Gathering Transmission Water Total (Thousands) Firm reservation fee revenues $ 109,933 $ 97,775 $ — $ 207,708 Volumetric-based fee revenues 127,457 9,159 — 136,616 Water services revenues — — 26,702 26,702 Total operating revenues $ 237,390 $ 106,934 $ 26,702 $ 371,026
Summary of Remaining Performance Obligations	The following table summarizes the transaction price allocated to EQM's remaining performance obligations under all contracts with firm reservation fees and MVCs as of March 31, 2019 . 2019 (a) 2020 2021 2022 2023 Thereafter Total (Thousands) Gathering firm reservation fees $ 353,984 $ 563,215 $ 573,214 $ 573,214 $ 573,214 $ 2,312,931 $ 4,949,772 Gathering revenues supported by MVCs 55,503 74,617 74,413 74,413 74,413 68,689 422,048 Transmission firm reservation fees 283,230 345,456 340,937 335,850 295,947 2,178,142 3,779,562 Total $ 692,717 $ 983,288 $ 988,564 $ 983,477 $ 943,574 $ 4,559,762 $ 9,151,382 (a) April 1, 2019 through December 31, 2019

Investment in Unconsolidated _2

Investment in Unconsolidated Entity (Tables)	3 Months Ended
	Mar. 31, 2019
Equity Method Investments and Joint Ventures [Abstract]
Schedule of Unaudited Condensed Financial Statements for the Investment in Unconsolidated Equity	The following tables summarize the unaudited condensed financial statements of the MVP Joint Venture. Condensed Consolidated Balance Sheets March 31, December 31, (Thousands) Current assets $ 696,893 $ 687,657 Non-current assets 3,526,691 3,223,220 Total assets $ 4,223,584 $ 3,910,877 Current liabilities $ 571,907 $ 617,355 Non-current liabilities 2,192 — Equity 3,649,485 3,293,522 Total liabilities and equity $ 4,223,584 $ 3,910,877 Condensed Statements of Consolidated Operations Three Months Ended 2019 2018 (Thousands) Environmental remediation reserve $ (2,192 ) $ — Other income 2,913 534 Net interest income 20,235 5,649 AFUDC - equity 47,216 13,182 Net income $ 68,172 $ 19,365

Net Income per Limited Partne_2

Net Income per Limited Partner Unit and Cash Distributions (Tables)	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Diluted	The following table presents EQM's calculation of net income per limited partner unit for common and Class B limited partner units. Three Months Ended 2019 2018 (1) (Thousands, except per unit data) Net income attributable to EQM $ 251,931 $ 260,350 Less pre-acquisition net income allocated to parent — (83,132 ) Less general partner interest in net income – general partner units — (3,117 ) Less general partner interest in net income – IDRs — (44,164 ) Limited partner interest in net income $ 251,931 $ 129,937 Net income allocable to common units $ 251,931 $ 129,937 Net income allocable to Class B units $ — $ — Weighted average limited partner common units outstanding - basic 154,259 80,607 Weighted average limited partner common units outstanding - diluted (2) 161,259 80,607 Net income per limited partner common unit - basic $ 1.63 $ 1.61 Net income per limited partner common unit - diluted $ 1.56 $ 1.61 (1) Net income attributable to the Drop-Down Transaction and the EQM-RMP Merger for the periods prior to May 1, 2018 and July 23, 2018, respectively, was not allocated to the limited partners for purposes of calculating net income per limited partner unit as these pre-acquisition amounts were not available to the EQM unitholders. (2) Includes 7,000,000 Class B units accounted for under the if-converted method as if the units were outstanding for the entire period. Class B units are not a participating security as they do not participate in distributions.
Schedule of Earnings Per Share, Basic	The following table presents EQM's calculation of net income per limited partner unit for common and Class B limited partner units. Three Months Ended 2019 2018 (1) (Thousands, except per unit data) Net income attributable to EQM $ 251,931 $ 260,350 Less pre-acquisition net income allocated to parent — (83,132 ) Less general partner interest in net income – general partner units — (3,117 ) Less general partner interest in net income – IDRs — (44,164 ) Limited partner interest in net income $ 251,931 $ 129,937 Net income allocable to common units $ 251,931 $ 129,937 Net income allocable to Class B units $ — $ — Weighted average limited partner common units outstanding - basic 154,259 80,607 Weighted average limited partner common units outstanding - diluted (2) 161,259 80,607 Net income per limited partner common unit - basic $ 1.63 $ 1.61 Net income per limited partner common unit - diluted $ 1.56 $ 1.61 (1) Net income attributable to the Drop-Down Transaction and the EQM-RMP Merger for the periods prior to May 1, 2018 and July 23, 2018, respectively, was not allocated to the limited partners for purposes of calculating net income per limited partner unit as these pre-acquisition amounts were not available to the EQM unitholders. (2) Includes 7,000,000 Class B units accounted for under the if-converted method as if the units were outstanding for the entire period. Class B units are not a participating security as they do not participate in distributions.

Financial Statements (Details)

Financial Statements (Details) - USD ($)	Feb. 13, 2019	Feb. 28, 2019	Mar. 31, 2019	Dec. 31, 2018
Cloud Computing Arrangements
Class of Stock [Line Items]
Useful life			7 years
Amortization expense related to implementation costs			$ 0
Common Units
Class of Stock [Line Items]
Canceled common units (in shares)	21,811,643
General Partner
Class of Stock [Line Items]
Exchange of equity interests			$ (43,782,000)
EQM | Common Units | EQGP
Class of Stock [Line Items]
Partners' capital common units outstanding (in shares)	21,811,643		21,811,643
EQM | Common Units | Equitrans Midstream Holdings, LLC
Class of Stock [Line Items]
Limited partner ownership interest (as a percent)			59.90%
Class B Units
Class of Stock [Line Items]
Canceled common units (in shares)			7,000,000	0
Class B Units | Common Units
Class of Stock [Line Items]
Exchange of equity interests			$ 1,477,000
IDR Merger Agreement
Class of Stock [Line Items]
Newly-issued common units (in shares)	80,000,000		80,000,000
IDR Merger Agreement | Class B Units
Class of Stock [Line Items]
Newly-issued common units (in shares)	7,000,000	7,000,000	7,000,000

Acquisitions and Mergers - Narr

Acquisitions and Mergers - Narrative (Details)		Mar. 31, 2019USD ($)	Mar. 13, 2019USD ($)mi	May 01, 2018USD ($)shares	Apr. 25, 2018USD ($)reporting_unitshares	Nov. 13, 2017USD ($)	Dec. 31, 2018USD ($)	Nov. 01, 2018USD ($)
Business Acquisition [Line Items]
Restricted cash	[1]	$ 50,000,000					$ 0
Initial purchase price		49,700,000
Goodwill		$ 1,123,813,000					1,123,813,000
Number of reporting units | reporting_unit					2
EQM $3 Billion Credit Facility | Line of credit
Business Acquisition [Line Items]
Credit facility								$ 3,000,000,000
Eureka Midstream Holdings, LLC
Business Acquisition [Line Items]
Length of gathering lines (in miles) | mi			190
Hornet Midstream Holdings, LLC
Business Acquisition [Line Items]
Length of gathering lines (in miles) | mi			15
Eureka Midstream, LLC | Line of credit
Business Acquisition [Line Items]
Credit facility			$ 400,000,000
Strike Force Midstream
Business Acquisition [Line Items]
Ownership interest (as a percent)				100.00%
Bolt-on Acquisition
Business Acquisition [Line Items]
Total consideration			1,030,000,000
Cash consideration			860,000,000
Pro-rata debt assumed			170,000,000
Restricted cash			$ 50,000,000
Bolt-on Acquisition | Eureka Midstream Holdings, LLC
Business Acquisition [Line Items]
Limited partner ownership interest (as a percent)			60.00%
Bolt-on Acquisition | Hornet Midstream Holdings, LLC
Business Acquisition [Line Items]
Limited partner ownership interest (as a percent)			100.00%
EQM-RMP Merger
Business Acquisition [Line Items]
Total consideration						$ 4,014,984,000
Goodwill						1,385,754,000	$ 1,123,813,000
EQM-RMP Merger | Rice Midstream Partners, LP
Business Acquisition [Line Items]
Common share conversation ratio					0.3319
Equity interest issued or issuable (in shares) | shares					34,000,000
EQM-RMP Merger | EQT
Business Acquisition [Line Items]
Measurement period adjustments increasing goodwill						$ 900,000
EQM-RMP Merger | EQM | EQT
Business Acquisition [Line Items]
Equity interest issued or issuable (in shares) | shares					9,544,530
May 2018 Acquisition
Business Acquisition [Line Items]
Cash consideration				$ 1,150,000,000
Equity interest issued or issuable (in shares) | shares				5,889,282
May 2018 Acquisition | Strike Force Midstream | Strike Force Midstream Holdings LLC
Business Acquisition [Line Items]
Ownership interest (as a percent)				75.00%
EQM-RMP Merger and Drop-Down Transaction
Business Acquisition [Line Items]
Goodwill					$ 1,384,900,000
Strike Force Midstream
Business Acquisition [Line Items]
Limited partner ownership interest (as a percent)				25.00%
Total consideration				$ 175,000,000
[1]	Includes $50.0 million of cash escrowed as of March 31, 2019 associated with the Bolt-on Acquisition (as defined in Note 2).

Acquisitions and Mergers - Sche

Acquisitions and Mergers - Schedule Fair Value of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Nov. 13, 2017	Dec. 31, 2018	Dec. 31, 2018	Mar. 31, 2019
Estimated Fair Value of Assets Acquired and Liabilities Assumed:
Goodwill		$ 1,123,813	$ 1,123,813	$ 1,123,813
EQM-RMP Merger
Business Acquisition [Line Items]
Estimated fair value of RMP, EQM Olympus, Strike Force and EQM WV	$ 4,014,984
Estimated Fair Value of Assets Acquired and Liabilities Assumed:
Current assets	132,459
Intangible assets	623,200
Property and equipment, net	2,265,900
Other non-current assets	118
Current liabilities	(117,124)
RMP $850 Million Facility	(266,000)
Other non-current liabilities	(9,323)
Total estimated fair value of assets acquired and liabilities assumed	2,629,230
Goodwill	1,385,754	1,123,813	1,123,813
Impairment of goodwill		$ 261,900	$ 261,941
Estimated fair value of noncontrolling interest	$ 166,000

Equity - Summary of Units Issue

Equity - Summary of Units Issued (Details) - shares	Feb. 13, 2019	Feb. 28, 2019	Mar. 31, 2019	Dec. 31, 2018
Increase (Decrease) in Partners' Capital
Balance at beginning (in shares)			121,900,653	82,024,773
Common units issued (in shares)				10,821
Drop-Down Transaction consideration (in shares)				5,889,282
Unit cancellation (in shares)			(8)
EQM IDR Transaction (in shares)			85,556,985
Balance at end (in shares)			207,457,630	121,900,653
IDR Merger Agreement
Increase (Decrease) in Partners' Capital
Newly-issued common units (in shares)	80,000,000		80,000,000
Class B Units | IDR Merger Agreement
Increase (Decrease) in Partners' Capital
Newly-issued common units (in shares)	7,000,000	7,000,000	7,000,000
EQM-RMP Merger
Increase (Decrease) in Partners' Capital
Common units issued (in shares)				33,975,777
Common Units
Increase (Decrease) in Partners' Capital
Common units issued (in shares)				10,821
Drop-Down Transaction consideration (in shares)				5,889,282
EQM IDR Transaction (in shares)			21,811,643
Common Units | EQM | EQGP
Increase (Decrease) in Partners' Capital
Partners' capital common units outstanding (in shares)	21,811,643		21,811,643
Common Units | Common Units
Increase (Decrease) in Partners' Capital
Balance at beginning (in shares)			120,457,638	80,581,758
Unit cancellation (in shares)			(8)
EQM IDR Transaction (in shares)			80,000,000
Balance at end (in shares)			200,457,630	120,457,638
Common Units | Class B Units
Increase (Decrease) in Partners' Capital
EQM IDR Transaction (in shares)			7,000,000
Balance at end (in shares)			7,000,000
Common Units | EQM-RMP Merger
Increase (Decrease) in Partners' Capital
Common units issued (in shares)				33,975,777
General Partner Units
Increase (Decrease) in Partners' Capital
Balance at beginning (in shares)			1,443,015	1,443,015
Common units issued (in shares)				0
Drop-Down Transaction consideration (in shares)				0
Unit cancellation (in shares)			0
EQM IDR Transaction (in shares)			(1,443,015)
Balance at end (in shares)			0	1,443,015
General Partner Units | Common Units
Increase (Decrease) in Partners' Capital
EQM IDR Transaction (in shares)			87,000,000
General Partner Units | EQM-RMP Merger
Increase (Decrease) in Partners' Capital
Common units issued (in shares)				0

Leases - Narrative (Details)

Leases - Narrative (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)lease_agreement	Jan. 01, 2019USD ($)
Lessee, Lease, Description [Line Items]
Operating lease, right-of-use asset	$ 34,800
Operating lease, liability	$ 34,895
Number of shared lease agreements | lease_agreement	2
Operating lease, right-of-use asset, current	$ 300
Operating lease, liability, current	$ 2,800
Weighted average remaining lease term	11 years
Weighted average discount rate (percentage)	6.00%
Accounting Standards Update 2016-02
Lessee, Lease, Description [Line Items]
Operating lease, right-of-use asset		$ 2,300
Operating lease, liability		$ 2,300
Shared Leases Assignment
Lessee, Lease, Description [Line Items]
Operating lease, right-of-use asset	$ 33,000

Equity - Narrative (Details)

Equity - Narrative (Details)	Mar. 13, 2019USD ($)day$ / sharesshares	Feb. 13, 2019shares	Feb. 28, 2019USD ($)shares	Mar. 31, 2019$ / sharesshares	Mar. 31, 2018$ / shares	Dec. 31, 2018shares
Class of Stock [Line Items]
Distributions paid to unitholders (dollars per common unit) | $ / shares				$ 1.13	$ 1.025
Convertible basis (percentage)	100.00%
Convertible units | $	$ 30,000,000
Threshold percentage of stock price trigger	140.00%
Threshold trading days | day	20
Threshold amount of stock price trigger (in shares)	500,000
Threshold consecutive trading days | day	20
Private Placement
Class of Stock [Line Items]
Aggregate number of units owned (in shares)	24,605,291
Cash purchase price for Series A Preferred Units (in dollars per share) | $ / shares	$ 48.77
Total gross proceeds for Series A Preferred Units | $	$ 1,200,000,000
Distributions paid to unitholders (dollars per common unit) | $ / shares	$ 1.0364
Cumulative quarterly distribution increasing percentage (B)	1.725%
IDR Merger Agreement
Class of Stock [Line Items]
Common units received (in shares)		80,000,000		80,000,000
Units convertible as of April 1, 2021 | $			$ 2,500,000
Units convertible as of April 1, 2022 | $			2,500,000
Units convertible as of April 1, 2023 | $			$ 2,000,000
Class B Units
Class of Stock [Line Items]
Common units outstanding (in shares)				7,000,000		0
Class B Units | IDR Merger Agreement
Class of Stock [Line Items]
Common units received (in shares)		7,000,000	7,000,000	7,000,000
ETRN | Class B Units
Class of Stock [Line Items]
Common units outstanding (in shares)				7,000,000
EQM | Private Placement
Class of Stock [Line Items]
Cash purchase price for Series A Preferred Units (in dollars per share) | $ / shares	$ 48.77
Cumulative quarterly distribution increasing percentage (A)	2.59%
EQM | Public Ownership Interest
Class of Stock [Line Items]
Limited partner ownership interest (as a percent)				40.10%
EQM | Common Units | Limited Partner Interest if Series A Preferred Units Were Converted
Class of Stock [Line Items]
Limited partner ownership interest (as a percent)				53.50%
EQM | Common Units | Equitrans Gathering Holdings, LLC
Class of Stock [Line Items]
Common units outstanding (in shares)				89,505,616
EQM | Common Units | Equitrans Gathering Holdings, LLC | Class B Units
Class of Stock [Line Items]
Common units outstanding (in shares)				6,153,907
EQM | Common Units | EQM GP Corporation
Class of Stock [Line Items]
Common units outstanding (in shares)				89,536
EQM | Common Units | EQM GP Corporation | Class B Units
Class of Stock [Line Items]
Common units outstanding (in shares)				6,155
EQM | Common Units | Equitrans Midstream Holdings, LLC
Class of Stock [Line Items]
Common units outstanding (in shares)				27,650,303
Limited partner ownership interest (as a percent)				59.90%
EQM | Common Units | Equitrans Midstream Holdings, LLC | Class B Units
Class of Stock [Line Items]
Common units outstanding (in shares)				839,938
EQM | Common Units | Equitrans Gathering Holdings, EQM GP Corporation, and Equitrans Midstream Holdings, LLC
Class of Stock [Line Items]
Limited partner ownership interest (as a percent)				56.50%
EQM | Common Units | Equitrans Gathering Holdings, EQM GP Corporation, and Equitrans Midstream Holdings, LLC | Class B Units
Class of Stock [Line Items]
Limited partner ownership interest (as a percent)				3.40%
EQM | Common Units | ETRN
Class of Stock [Line Items]
Common units outstanding (in shares)				117,245,455
Limited partner ownership interest (as a percent)				59.90%

Leases - Schedule of Operating

Leases - Schedule of Operating Lease Cost (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Leases [Abstract]
Operating lease cost	$ 1,297
Short-term lease cost	368
Variable lease cost	8
Total lease cost	$ 1,673

Leases - Schedule of Operatin_2

Leases - Schedule of Operating Lease Liability Maturities (Details) $ in Thousands	Mar. 31, 2019USD ($)
Leases [Abstract]
2019	$ 3,702
2020	4,218
2021	4,070
2022	4,117
2023	3,841
2024	3,889
Thereafter	24,729
Total	48,566
Less: imputed interest	13,671
Present value of operating lease liability	$ 34,895

Financial Information by Busi_3

Financial Information by Business Segment - Narrative (Details)	3 Months Ended
	Mar. 31, 2019business_linesegment
Segment Reporting [Abstract]
Number of business segments | segment	3
Number of lines of business | business_line	3

Financial Information by Busi_4

Financial Information by Business Segment - Schedule of Segment Information (Details) - USD ($) $ in Thousands		Mar. 31, 2019	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Revenues from external customers (including related parties):
Total operating revenues	[1],[2]		$ 389,782	$ 371,026
Operating income:
Total operating income	[1]		268,014	265,798
Reconciliation of operating income to net income:
Equity income	[1],[3],[4]		31,063	8,811
Other income	[1]		2,210	904
Net interest expense	[1],[5]		49,356	12,670
Net income	[1],[6]		251,931	262,843
Segment assets:
Total assets		$ 9,888,585	9,888,585		$ 9,456,121
Depreciation:
Depreciation	[1],[3]		47,065	41,280
Expenditures for segment assets:
Accrued capital expenditures		137,800	137,800	75,500	108,900	$ 90,700
Operating Segments
Segment assets:
Total assets		9,720,493	9,720,493		9,315,915
Depreciation:
Depreciation			47,065	41,280
Expenditures for segment assets:
Expenditures for segment assets			235,654	155,442
Headquarters, including cash
Segment assets:
Total assets		168,092	168,092		140,206
Gathering
Revenues from external customers (including related parties):
Total operating revenues			261,881	237,390
Gathering | Operating Segments
Revenues from external customers (including related parties):
Total operating revenues			261,881	237,390
Operating income:
Total operating income			182,078	171,035
Segment assets:
Total assets		6,234,581	6,234,581		6,011,654
Depreciation:
Depreciation			28,116	23,068
Expenditures for segment assets:
Expenditures for segment assets			207,717	134,138
Transmission
Revenues from external customers (including related parties):
Total operating revenues			109,859	106,934
Transmission | Operating Segments
Revenues from external customers (including related parties):
Total operating revenues			109,859	106,934
Operating income:
Total operating income			84,750	79,451
Segment assets:
Total assets		3,243,578	3,243,578		3,066,659
Depreciation:
Depreciation			12,533	12,441
Expenditures for segment assets:
Expenditures for segment assets			18,762	18,929
Water
Revenues from external customers (including related parties):
Total operating revenues			18,042	26,702
Water | Operating Segments
Revenues from external customers (including related parties):
Total operating revenues			18,042	26,702
Operating income:
Total operating income			1,186	15,312
Segment assets:
Total assets		242,334	242,334		$ 237,602
Depreciation:
Depreciation			6,416	5,771
Expenditures for segment assets:
Expenditures for segment assets			$ 9,175	$ 2,375
ETRN
Expenditures for segment assets:
Expenditures for segment assets		$ 49,700
[1]	As discussed in Notes 1 and 2, the consolidated financial statements of EQM have been retrospectively recast to include the pre-acquisition results of EQM Olympus Midstream LLC (EQM Olympus), Strike Force Midstream Holdings LLC (Strike Force) and EQM West Virginia Midstream LLC (EQM WV), which were acquired by EQM effective on May 1, 2018 (the Drop-Down Transaction), and Rice Midstream Partners LP (RMP), which was acquired by EQM effective on July 23, 2018 (the EQM-RMP Merger), because these transactions were between entities under common control
[2]	Operating revenues included related party revenues from EQT Corporation (NYSE: EQT) (EQT) of $284.5 million and $265.6 million for the three months ended March 31, 2019 and 2018, respectively. See Note 7.
[3]	As discussed in Notes 1 and 2, the consolidated financial statements of EQM have been retrospectively recast to include the pre-acquisition results of the Drop-Down Transaction and the EQM-RMP Merger because these transactions were between entities under common control.
[4]	Represents equity income from Mountain Valley Pipeline, LLC (the MVP Joint Venture). See Note 8.
[5]	Net interest expense included interest income on the Preferred Interest in EQT Energy Supply, LLC (EES) of $1.6 million and $1.7 million for the three months ended March 31, 2019 and 2018, respectively.
[6]	As discussed in Notes 1 and 2, the consolidated financial statements of EQM have been retrospectively recast to include the pre-acquisition results of the Drop-Down Transaction and the EQM-RMP Merger because these transactions were between entities under common control.

Revenue from Contracts with C_3

Revenue from Contracts with Customers - Narrative (Details)	3 Months Ended
	Mar. 31, 2019
Gathering
Disaggregation of Revenue [Line Items]
Weighted average remaining term	11 years
Transmission
Disaggregation of Revenue [Line Items]
Weighted average remaining term	15 years

Revenue from Contracts with C_4

Revenue from Contracts with Customers - Schedule of Disaggregated Revenue Information, by Business Segment (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Total operating revenues	[1],[2]	$ 389,782	$ 371,026
Firm reservation fee revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		228,183	207,708
Volumetric-based fee revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		143,557	136,616
Gathering
Disaggregation of Revenue [Line Items]
Total operating revenues		261,881	237,390
Gathering | Firm reservation fee revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		128,959	109,933
Gathering | Volumetric-based fee revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		132,922	127,457
Transmission
Disaggregation of Revenue [Line Items]
Total operating revenues		109,859	106,934
Transmission | Firm reservation fee revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		99,224	97,775
Transmission | Volumetric-based fee revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		10,635	9,159
Water
Disaggregation of Revenue [Line Items]
Total operating revenues		18,042	26,702
Water | Firm reservation fee revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		0	0
Water | Volumetric-based fee revenues
Disaggregation of Revenue [Line Items]
Total operating revenues		$ 0	$ 0
[1]	As discussed in Notes 1 and 2, the consolidated financial statements of EQM have been retrospectively recast to include the pre-acquisition results of EQM Olympus Midstream LLC (EQM Olympus), Strike Force Midstream Holdings LLC (Strike Force) and EQM West Virginia Midstream LLC (EQM WV), which were acquired by EQM effective on May 1, 2018 (the Drop-Down Transaction), and Rice Midstream Partners LP (RMP), which was acquired by EQM effective on July 23, 2018 (the EQM-RMP Merger), because these transactions were between entities under common control
[2]	Operating revenues included related party revenues from EQT Corporation (NYSE: EQT) (EQT) of $284.5 million and $265.6 million for the three months ended March 31, 2019 and 2018, respectively. See Note 7.

Revenue from Contracts with C_5

Revenue from Contracts with Customers - Summary of Remaining Performance Obligations (Details) $ in Thousands	Mar. 31, 2019USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	$ 692,717
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	983,288
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	988,564
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	983,477
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	943,574
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	4,559,762
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	9,151,382
Transmission | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	$ 283,230
Remaining performance obligations, expected timing	9 months
Transmission | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	$ 345,456
Remaining performance obligations, expected timing	1 year
Transmission | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	$ 340,937
Remaining performance obligations, expected timing	1 year
Transmission | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	$ 335,850
Remaining performance obligations, expected timing	1 year
Transmission | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	$ 295,947
Remaining performance obligations, expected timing	1 year
Transmission | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	$ 2,178,142
Remaining performance obligations, expected timing
Transmission | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	$ 3,779,562
Gathering firm reservation fees | Gathering | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	$ 353,984
Remaining performance obligations, expected timing	9 months
Gathering firm reservation fees | Gathering | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	$ 563,215
Remaining performance obligations, expected timing	1 year
Gathering firm reservation fees | Gathering | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	$ 573,214
Remaining performance obligations, expected timing	1 year
Gathering firm reservation fees | Gathering | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	$ 573,214
Remaining performance obligations, expected timing	1 year
Gathering firm reservation fees | Gathering | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	$ 573,214
Remaining performance obligations, expected timing	1 year
Gathering firm reservation fees | Gathering | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	$ 2,312,931
Remaining performance obligations, expected timing
Gathering firm reservation fees | Gathering | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	$ 4,949,772
Minimum volume commitment contract | Gathering | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	$ 55,503
Remaining performance obligations, expected timing	9 months
Minimum volume commitment contract | Gathering | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	$ 74,617
Remaining performance obligations, expected timing	1 year
Minimum volume commitment contract | Gathering | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	$ 74,413
Remaining performance obligations, expected timing	1 year
Minimum volume commitment contract | Gathering | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	$ 74,413
Remaining performance obligations, expected timing	1 year
Minimum volume commitment contract | Gathering | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	$ 74,413
Remaining performance obligations, expected timing	1 year
Minimum volume commitment contract | Gathering | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	$ 68,689
Minimum volume commitment contract | Gathering | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total	$ 422,048

Related Party Transactions (Det

Related Party Transactions (Details)	Mar. 31, 2019
EQT | Equitrans Midstream Holdings, LLC
Related Party Transaction [Line Items]
Ownership interest	19.90%

Investment in Unconsolidated _3

Investment in Unconsolidated Entity - Narrative (Details) $ in Thousands		1 Months Ended		3 Months Ended
		Apr. 30, 2019USD ($)	Mar. 31, 2019USD ($)mi	Mar. 31, 2019USD ($)mi	Mar. 31, 2018USD ($)	Jun. 30, 2019USD ($)	May 31, 2019USD ($)	Feb. 28, 2019USD ($)	Jan. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Apr. 30, 2018mi
Schedule of Equity Method Investments [Line Items]
Expected capital call notice to be paid			$ 156,412	$ 156,412						$ 169,202
Capital call notice expected to be paid	[1]			$ 144,763	$ 117,019
MVP Joint Venture | Variable Interest Entity, Not Primary Beneficiary
Schedule of Equity Method Investments [Line Items]
Ownership interest			45.50%	45.50%
Maximum financial statement exposure			$ 1,792,000	$ 1,792,000
MVP Southgate Project | Variable Interest Entity, Not Primary Beneficiary
Schedule of Equity Method Investments [Line Items]
Ownership interest			47.20%	47.20%
Capital contribution payable to MVP Joint Venture				$ 6,600
MVP Southgate Project | Variable Interest Entity, Not Primary Beneficiary | Subsequent Event
Schedule of Equity Method Investments [Line Items]
Capital call notice expected to be paid		$ 800
MVP Southgate Project | Variable Interest Entity, Not Primary Beneficiary | Scenario, Forecast
Schedule of Equity Method Investments [Line Items]
Expected capital call notice to be paid						$ 4,600	$ 1,200
MVP Project | Variable Interest Entity, Not Primary Beneficiary
Schedule of Equity Method Investments [Line Items]
Capital contribution payable to MVP Joint Venture			$ 149,800
MVP Project | Variable Interest Entity, Not Primary Beneficiary | Scenario, Forecast
Schedule of Equity Method Investments [Line Items]
Expected capital call notice to be paid						$ 124,300	$ 25,500
MVP
Schedule of Equity Method Investments [Line Items]
Length of pipeline (in miles) | mi			300	300
MVP | Variable Interest Entity, Not Primary Beneficiary
Schedule of Equity Method Investments [Line Items]
Issuance of performance guarantee, remaining capital obligation, percentage								33.00%	33.00%
Issuance of performance guarantee			$ 261,000	$ 261,000					$ 261,000
MVP Southgate Project | EQM
Schedule of Equity Method Investments [Line Items]
Length of pipeline (in miles) | mi											70
MVP Southgate Project | Variable Interest Entity, Not Primary Beneficiary
Schedule of Equity Method Investments [Line Items]
Issuance of performance guarantee								$ 14,000
Beneficial Owner | MVP Joint Venture
Schedule of Equity Method Investments [Line Items]
Percentage of ownership interest				66.67%
[1]	As discussed in Notes 1 and 2, the consolidated financial statements of EQM have been retrospectively recast to include the pre-acquisition results of the Drop-Down Transaction and the EQM-RMP Merger because these transactions were between entities under common control.

Investment in Unconsolidated _4

Investment in Unconsolidated Entity - Schedule of Unaudited Condensed Financial Statements for the Investment in Unconsolidated Equity (Details) - MVP Joint Venture - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Condensed Consolidated Balance Sheets
Current assets	$ 696,893		$ 687,657
Non-current assets	3,526,691		3,223,220
Total assets	4,223,584		3,910,877
Current liabilities	571,907		617,355
Non-current liabilities	2,192		0
Equity	3,649,485		3,293,522
Total liabilities and equity	4,223,584		$ 3,910,877
Condensed Statements of Consolidated Operations
Environmental remediation reserve	(2,192)	$ 0
Other income	2,913	534
Net interest income	20,235	5,649
AFUDC - equity	47,216	13,182
Net income	$ 68,172	$ 19,365

Debt - $3 Billion Facility (Det

Debt - $3 Billion Facility (Details)	3 Months Ended
	Mar. 31, 2019USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2018USD ($)	Oct. 31, 2018USD ($)
Debt Instrument [Line Items]
Letters of credit outstanding	$ 1,082,000,000		$ 625,000,000
$3 Billion Credit Facility | Revolving Credit Facility
Debt Instrument [Line Items]
Letters of credit outstanding	1,000,000		1,000,000
Borrowings outstanding	1,100,000,000		$ 625,000,000
$3 Billion Credit Facility | Line of credit
Debt Instrument [Line Items]
Maximum borrowing capacity	3,000,000,000
Additional borrowing capacity	$ 750,000,000
Consolidated leverage ratio for certain measurement periods (not more than)	5
Consolidated leverage ratio (not more than)	5.50
Maximum amount of outstanding short-term loans at any time during the period	$ 1,100,000,000	$ 420,000,000
Average daily balance of short-term loans outstanding	$ 942,000,000	$ 301,000,000
Weighted average annual interest rate	3.90%	3.00%
$3 Billion Credit Facility | Same-day swing line advances
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 250,000,000
$3 Billion Credit Facility | Letter of credit
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 400,000,000
$1 Billion Credit Facility | Line of credit
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 1,000,000,000

Debt - EQM Term Loan Facility (

Debt - EQM Term Loan Facility (Details) - Line of credit - $2.5 Billion EQM Term Loan Facility - USD ($)	Apr. 25, 2018	Jun. 25, 2018	Jun. 25, 2018
Short-term Debt [Line Items]
Maximum borrowing capacity	$ 2,500,000,000
Line of credit expiration period	364 days
Write off of deferred issuance costs			$ 3,000,000
Maximum amount of outstanding short-term loans at any time during the period		$ 1,825,000,000
Average daily balance of short-term loans outstanding		$ 1,231,000,000
Weighted average annual interest rate		3.30%

Debt - RMP $850 Million Facilit

Debt - RMP $850 Million Facility (Details) - USD ($)		Jul. 23, 2018	Mar. 31, 2019	Mar. 31, 2018
Debt Instrument [Line Items]
Document Period End Date			Mar. 31, 2019
Repayment of borrowings outstanding	[1]		$ 145,000,000	$ 128,000,000
RMP $850 Million Facility | Line of credit
Debt Instrument [Line Items]
Maximum borrowing capacity			850,000,000
Repayment of borrowings outstanding		$ 260,000,000
Maximum amount of outstanding short-term loans at any time during the period			336,000,000
Average daily balance of short-term loans outstanding			$ 308,000,000
Weighted average annual interest rate			3.60%
[1]	As discussed in Notes 1 and 2, the consolidated financial statements of EQM have been retrospectively recast to include the pre-acquisition results of the Drop-Down Transaction and the EQM-RMP Merger because these transactions were between entities under common control.

Debt - EQM 4.125% and 4.00% Sen

Debt - EQM 4.125% and 4.00% Senior Notes (Details) - USD ($)	Mar. 31, 2019	Dec. 31, 2016	Sep. 30, 2014
Senior Notes | EQM 4.125% Senior Notes due 2026
Debt Instrument [Line Items]
Interest rate (as a percent)	4.125%	4.125%
Aggregate principal amount		$ 500,000,000
Senior Notes | EQM 4.00 Senior Notes Due 2024
Debt Instrument [Line Items]
Interest rate (as a percent)	4.00%		4.00%
Aggregate principal amount			$ 500,000,000
Line of credit | $3 Billion Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 3,000,000,000

Debt - 2018 Senior Notes (Detai

Debt - 2018 Senior Notes (Details) - USD ($)	3 Months Ended
	Jun. 30, 2018	Mar. 31, 2019
Senior Notes
Debt Instrument [Line Items]
Net proceeds from offering	$ 2,465,800,000
Discount	11,800,000
Debt issuance costs	$ 22,400,000
Senior Notes | EQM 4.75% Senior Notes Due 2023
Debt Instrument [Line Items]
Interest rate (as a percent)	4.75%
Aggregate principal amount	$ 1,100,000,000
Senior Notes | EQM 5.50% Senior Notes Due 2028
Debt Instrument [Line Items]
Interest rate (as a percent)	5.50%
Aggregate principal amount	$ 850,000,000
Senior Notes | EQM 6.50% Senior Notes Due 2048
Debt Instrument [Line Items]
Interest rate (as a percent)	6.50%
Aggregate principal amount	$ 550,000,000
Line of credit | RMP $850 Million Facility
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 850,000,000

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
EES | Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Value of preferred interest	$ 114	$ 115
Level 3 | EES | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Value of preferred interest	124	122
Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of long-term debt	3,458	3,457
Fair Value, Measurements, Recurring | Level 2 | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of long-term debt	$ 3,504	$ 3,425

Net Income per Limited Partne_3

Net Income per Limited Partner Unit and Cash Distributions - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions		Apr. 23, 2019	Apr. 30, 2019	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Distribution Made to Limited Partner [Line Items]
Cash distribution to the company's common and subordinated unitholders declared (in dollars per share)	[1],[2]			$ 1.145	$ 1.065
Class B Units
Distribution Made to Limited Partner [Line Items]
Common units outstanding (in shares)				7,000,000		0
Subsequent Event
Distribution Made to Limited Partner [Line Items]
Cash distribution to the company's common and subordinated unitholders declared (in dollars per share)		$ 1.145
Limited Partner | Subsequent Event
Distribution Made to Limited Partner [Line Items]
Cash distribution declared to the limited partner			$ 134.2
Phantom Share Units (PSUs)
Distribution Made to Limited Partner [Line Items]
Weighted average phantom unit awards included in the calculation of basic weighted average limited partner units outstanding (in shares)				21,908	22,748
[1]	As discussed in Notes 1 and 2, the consolidated financial statements of EQM have been retrospectively recast to include the pre-acquisition results of EQM Olympus Midstream LLC (EQM Olympus), Strike Force Midstream Holdings LLC (Strike Force) and EQM West Virginia Midstream LLC (EQM WV), which were acquired by EQM effective on May 1, 2018 (the Drop-Down Transaction), and Rice Midstream Partners LP (RMP), which was acquired by EQM effective on July 23, 2018 (the EQM-RMP Merger), because these transactions were between entities under common control
[2]	Represents the cash distributions declared related to the period presented. See Note 11.

Net Income per Limited Partne_4

Net Income per Limited Partner Unit and Cash Distributions - Schedule of Net Income Per Limited Partner Unit (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to EQM	[1]	$ 251,931	$ 260,350
Less pre-acquisition net income allocated to EQT	[1]	0	(83,132)
Less general partner interest in net income – general partner units	[1]	0	(3,117)
Less general partner interest in net income – IDRs	[1]	0	(44,164)
Limited partner interest in net income	[1]	251,931	129,937
Net income allocable to units	[1]	$ 251,931	$ 129,937
Weighted average limited partner common units outstanding – basic (in shares)	[1]	154,259,000	80,607,000
Weighted average limited partner common units outstanding – diluted (in shares)	[1]	161,259,000	80,607,000
Net income per limited partner common unit – basic (in dollars per share)	[1]	$ 1.63	$ 1.61
Net income per limited partner common unit – diluted (in dollars per share)	[1]	$ 1.56	$ 1.61
Common Units
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Limited partner interest in net income	[1]	$ 251,931	$ 129,937
Net income allocable to units	[1]	$ 251,931	129,937
Common units outstanding (in shares)		200,457,630		120,457,638
Class B Units
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Limited partner interest in net income	[1]	$ 0	0
Net income allocable to units	[1]	$ 0	$ 0
Common units outstanding (in shares)		7,000,000		0
[1]	As discussed in Notes 1 and 2, the consolidated financial statements of EQM have been retrospectively recast to include the pre-acquisition results of EQM Olympus Midstream LLC (EQM Olympus), Strike Force Midstream Holdings LLC (Strike Force) and EQM West Virginia Midstream LLC (EQM WV), which were acquired by EQM effective on May 1, 2018 (the Drop-Down Transaction), and Rice Midstream Partners LP (RMP), which was acquired by EQM effective on July 23, 2018 (the EQM-RMP Merger), because these transactions were between entities under common control