Dominion Energy Midstream Partners 10-Q 4 May 17 2017 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2017	Apr. 14, 2017
Document and Entity Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q1
Trading Symbol	DM
Entity Registrant Name	Dominion Midstream Partners, LP
Entity Central Index Key	1,603,286
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Units Outstanding
Document and Entity Information [Line Items]
Entity Units Outstanding		67,249,267
Entity Subordinated Units Outstanding
Document and Entity Information [Line Items]
Entity Units Outstanding		31,972,789

Consolidated Statements of Inco

Consolidated Statements of Income (Unaudited) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Operating revenue	[1]	$ 130.2	$ 83
Operating Expenses
Purchased gas	[1]	12.2	0.9
Other operations and maintenance:
Affiliated suppliers		15.6	9.4
Other		15.5	10.6
Depreciation and amortization		24.9	10
Other taxes		9.3	7.3
Total operating expenses		77.5	38.2
Income from operations		52.7	44.8
Earnings from equity method investees		8	6.4
Other income		1.3	0.5
Interest and related charges (benefit)	[1]	7.7	(0.1)
Net income including noncontrolling interest and predecessors		54.3	51.8
Less: Net income attributable to noncontrolling interest		2.1	28.7
Net income attributable to partners		52.2	23.1
Net income attributable to partners' ownership interest
Net income attributable to limited partners		9.5
General partner's interest in net income		2.7	0.4
Convertible Preferred Units
Net income attributable to partners' ownership interest
Net income attributable to limited partners		9.5
Common Units
Net income attributable to partners' ownership interest
Net income attributable to limited partners		$ 27.1	$ 13.4
Net income per limited partner unit (basic)
Net income per limited partner unit (basic) (in dollars per unit)		$ 0.40	$ 0.29
Net income per limited partner unit (diluted)
Net income per limited partner unit (diluted) (in dollars per unit)		$ 0.37	$ 0.29
Subordinated Units
Net income attributable to partners' ownership interest
Net income attributable to limited partners		$ 12.9	$ 9.3
Net income per limited partner unit (basic)
Net income per limited partner unit (basic) (in dollars per unit)		$ 0.40	$ 0.29
Net income per limited partner unit (diluted)
Net income per limited partner unit (diluted) (in dollars per unit)		$ 0.40	$ 0.29
[1]	See Note 15 for amounts attributable to related parties.

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income including noncontrolling interest and predecessors	$ 54.3	$ 51.8
Other comprehensive loss:
Net deferred losses on derivatives-hedging activities	(0.5)	0
Other comprehensive loss	(0.5)	0
Comprehensive income including noncontrolling interest and predecessors	53.8	51.8
Comprehensive income attributable to noncontrolling interests	2.1	28.7
Comprehensive income attributable to partners	$ 51.7	$ 23.1

Consolidated Balance Sheets (Un

Consolidated Balance Sheets (Unaudited) - USD ($) $ in Millions		Mar. 31, 2017	Dec. 31, 2016	[1]
Current Assets
Cash and cash equivalents		$ 91.1	$ 39.6
Restricted cash		25	25
Customer and other receivables		31.7	45.9
Affiliated receivables		12.7	18.3
Inventories		22	20.1
Regulatory assets		6	5.1
Other		9.9	16.9
Total current assets		198.4	170.9
Investment in Equity Method Affiliates		258.8	257.8
Property, Plant and Equipment
Property, plant and equipment		7,259.2	6,911.4
Accumulated depreciation and amortization		(1,052.2)	(1,032)
Total property, plant and equipment, net		6,207	5,879.4
Deferred Charges and Other Assets
Goodwill		819.2	819.2
Regulatory assets		40.6	40.2
Other	[2]	20.3	19.4
Total deferred charges and other assets		880.1	878.8
Total assets		7,544.3	7,186.9
Current Liabilities
Securities due within one year		250	0
Accounts payable		18.9	21.5
Payables to affiliates		8.5	9.9
Regulatory liabilities		8	7.5
Dominion credit facility borrowings		67.9	63.2
Deferred revenue		1.7	4.3
Other		43.3	42.8
Total current liabilities		398.3	149.2
Long-Term Debt		479.8	729.9
Deferred Credits and Other Liabilities
Regulatory liabilities		130.7	129.1
Deferred revenue		13.8	14
Other	[2]	68.8	64.8
Total deferred credits and other liabilities		213.3	207.9
Total liabilities		1,091.4	1,087
Commitments and Contingencies
Equity and Partners' Capital
Accumulated other comprehensive loss		(0.9)	(0.4)
Total Dominion Midstream Partners, LP partners' capital		2,807.4	2,786.2
Noncontrolling interest		3,645.5	3,313.7
Total equity and partners' capital		6,452.9	6,099.9
Total liabilities and equity and partners' capital		7,544.3	7,186.9
Limited Partners
Equity and Partners' Capital
Preferred unitholders		496	492.1
Limited Partners | Common Units
Equity and Partners' Capital
Common unitholders and Subordinated unitholder		1,089	1,082.1
Dominion | Limited Partners
Equity and Partners' Capital
Preferred unitholders		303.6	301.2
Dominion | Limited Partners | Common Units
Equity and Partners' Capital
Common unitholders and Subordinated unitholder		460.1	457.4
Dominion | Limited Partners | Subordinated Units
Equity and Partners' Capital
Common unitholders and Subordinated unitholder		487.6	483
Dominion | General Partner Dominion (non-economic interest)
Equity and Partners' Capital
General Partner interest - Dominion (non-economic interest)		$ (28)	$ (29.2)
[1]	Dominion Midstream's Consolidated Balance Sheet at December 31, 2016 has been derived from the audited Consolidated Balance Sheet at that date.
[2]	See Note 15 for amounts attributable to related parties.

Consolidated Balance Sheets (U5

Consolidated Balance Sheets (Unaudited) (Parenthetical) - shares	Mar. 31, 2017	Dec. 31, 2016
Preferred unitholders- units issued	18,942,714	18,942,714
Preferred unitholders- units outstanding	18,942,714	18,942,714
Dominion
Preferred unitholders- units issued	11,365,628	11,365,628
Preferred unitholders- units outstanding	11,365,628	11,365,628
Common Units
Common unitholders and Subordinated unitholder - units issued	48,744,639	48,734,195
Common unitholders and Subordinated unitholder- units outstanding	48,744,639	48,734,195
Common Units | Dominion
Common unitholders and Subordinated unitholder - units issued	18,504,628	18,504,628
Common unitholders and Subordinated unitholder- units outstanding	18,504,628	18,504,628
Subordinated Units | Dominion
Common unitholders and Subordinated unitholder - units issued	31,972,789	31,972,789
Common unitholders and Subordinated unitholder- units outstanding	31,972,789	31,972,789

Consolidated Statement of Equit

Consolidated Statement of Equity and Partners' Capital (Unaudited) - USD ($) $ in Millions	Total		Total Dominion Midstream Partners, LP Partners' Equity and Capital	Preferred StockPreferred Unitholders PublicLimited Partners	Preferred StockPreferred Unitholder DominionLimited Partners	Common Unitholders and Subordinated UnitholderCommon UnitsLimited Partners	Common Unitholders and Subordinated UnitholderCommon UnitsCommon Unitholder and Subordinated Unitholder- Dominion	Common Unitholders and Subordinated UnitholderSubordinated UnitsCommon Unitholder and Subordinated Unitholder- Dominion	General Partner Dominion (non-economic interest)General Partner Dominion (non-economic interest)	AOCI	Noncontrolling interest
Balance at Dec. 31, 2015	$ 3,641		$ 1,502.6	$ 0	$ 0	$ 600.8	$ 438.8	$ 475.4	$ (12.4)	$ 0	$ 2,138.4
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income including noncontrolling interest and predecessors	51.8		23.1			8.1	5.3	9.3	0.4		28.7
Equity contributions from Dominion	244.9		0								244.9
Purchase of common units by Dominion	0		0			(8.1)	8.1
Distributions	(16.8)		(16.8)			(5.9)	(3.9)	(6.8)	(0.2)
Other comprehensive loss	0
Unit awards (net of unearned compensation)	0.1		0.1			0.1
Other	0.1		0								0.1
Balance at Mar. 31, 2016	3,921.1		1,509	0	0	595	448.3	477.9	(12.2)	0	2,412.1
Balance at Dec. 31, 2016	6,099.9	[1]	2,786.2	492.1	301.2	1,082.1	457.4	483	(29.2)	(0.4)	3,313.7
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income including noncontrolling interest and predecessors	54.3		52.2	5.9	3.6	19.6	7.5	12.9	2.7		2.1
Equity contributions from Dominion	329.4		0.2						0.2		329.2
Distributions	(30.7)		(30.7)	(2)	(1.2)	(12.7)	(4.8)	(8.3)	(1.7)
Other comprehensive loss	(0.5)		(0.5)							(0.5)
Unit awards (net of unearned compensation)	0.1		0.1	0.1
Other	0.4		(0.1)	(0.1)							0.5
Balance at Mar. 31, 2017	$ 6,452.9		$ 2,807.4	$ 496	$ 303.6	$ 1,089	$ 460.1	$ 487.6	$ (28)	$ (0.9)	$ 3,645.5
[1]	Dominion Midstream's Consolidated Balance Sheet at December 31, 2016 has been derived from the audited Consolidated Balance Sheet at that date.

Consolidated Statements of Cash

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017		Mar. 31, 2016
Operating Activities
Net income including noncontrolling interest and predecessors	$ 54.3		$ 51.8
Adjustments to reconcile net income including noncontrolling interest and predecessors to net cash provided by operating activities:
Depreciation and amortization	24.9		10
Other adjustments to income, net	(1.8)		(1.1)
Changes in:
Customer and other receivables	14.2		1.1
Affiliated receivables	5.6		0
Prepayments	1.8		5
Accounts payable	4.6		1.8
Payables to affiliates	(1.4)		3.4
Accrued interest, payroll and taxes	2.1		(3.1)
Other operating assets and liabilities	6		(0.4)
Net cash provided by operating activities	110.3		68.5
Investing Activities
Plant construction and other property additions	(361.1)		(299.7)
Other	(0.7)		(0.1)
Net cash used in investing activities	(361.8)		(299.8)
Financing Activities
Dominion credit facility borrowings, net	4.7		3.6
Contributions from Dominion	329.2		244.9
Other	(0.2)		0
Net cash provided by financing activities	303		231.7
Increase in cash and cash equivalents	51.5		0.4
Cash and cash equivalents at beginning of period	39.6	[1]	35
Cash and cash equivalents at end of period	91.1		35.4
Significant noncash investing and financing activities:
Accrued capital expenditures	16.2		14.9
Equity contributions from Dominion to relieve payables to affiliates
Significant noncash investing and financing activities:
Equity contributions from Dominion to relieve payables to affiliates	0.2		0
Preferred Unitholders
Financing Activities
Distributions to unitholders	(3.2)		0
Limited Partners | Common Units
Financing Activities
Distributions to unitholders	(17.5)		(9.8)
Limited Partners | Subordinated Units
Financing Activities
Distributions to unitholders	(8.3)		(6.8)
General Partner (including IDRs)
Financing Activities
Distributions to unitholders	$ (1.7)		$ (0.2)
[1]	Dominion Midstream's Consolidated Balance Sheet at December 31, 2016 has been derived from the audited Consolidated Balance Sheet at that date.

Description of Business and Bas

Description of Business and Basis of Presentation	3 Months Ended
	Mar. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business and Basis of Presentation	Description of Business and Basis of Presentation Description of Business Dominion Midstream is a Delaware limited partnership formed in March 2014 by Dominion MLP Holding Company, LLC and Dominion Midstream GP, LLC, both indirect wholly-owned subsidiaries of Dominion, to grow a portfolio of natural gas terminaling, processing, storage, transportation and related assets. Dominion Midstream holds the Preferred Equity Interest and non-economic general partner interest in Cove Point, the owner and operator of the Cove Point LNG Facility and the Cove Point Pipeline. The Preferred Equity Interest is a perpetual, non-convertible preferred equity interest entitled to Preferred Return Distributions so long as Cove Point has sufficient cash and undistributed Net Operating Income (determined on a cumulative basis from the closing of the Offering) from which to make Preferred Return Distributions. Preferred Return Distributions are made on a quarterly basis and are not cumulative. The Preferred Equity Interest is also entitled to the Additional Return Distributions. In addition, Dominion Midstream owns DCG and a 25.93% noncontrolling partnership interest in Iroquois, both of which are FERC-regulated interstate natural gas pipelines. In December 2016, Dominion Midstream acquired from Dominion all of the issued and outstanding membership interests in Questar Pipeline as described further in Note 2. Questar Pipeline owns and operates nearly 2,200 miles of interstate natural gas pipelines and 18 transmission and storage compressor stations in the western U.S. Basis of Presentation The contribution by Dominion to Dominion Midstream of the general partner interest in Cove Point and a portion of the Preferred Equity Interest is considered to be a reorganization of entities under common control. As a result, Dominion Midstream’s basis is equal to Dominion’s cost basis in the general partner interest in Cove Point and a portion of the Preferred Equity Interest. As discussed in Note 14 to the Consolidated Financial Statements in Dominion Midstream’s Annual Report on Form 10-K for the year ended December 31, 2016, Dominion Midstream is the primary beneficiary of, and therefore consolidates, Cove Point. As such, Dominion Midstream’s investment in the Preferred Equity Interest and Cove Point's preferred equity interest are eliminated in consolidation. Dominion's retained common equity interest in Cove Point is reflected as noncontrolling interest. The Questar Pipeline Acquisition is considered to be a reorganization of entities under common control. As a result, Dominion Midstream’s basis in Questar Pipeline is equal to Dominion’s cost basis in the assets and liabilities of Questar Pipeline. On December 1, 2016, Questar Pipeline became a wholly-owned subsidiary of Dominion Midstream and is therefore consolidated by Dominion Midstream. The accompanying financial statements and related notes include the historical results and financial position of Questar Pipeline beginning September 16, 2016, the inception date of common control. The financial statements for all periods presented include costs for certain general, administrative and corporate expenses assigned by DRS, DCGS or QPC Services Company to Dominion Midstream on the basis of direct and allocated methods in accordance with Dominion Midstream's services agreements with DRS, DCGS and QPC Services Company. Where costs incurred cannot be determined by specific identification, the costs are allocated based on the proportional level of effort devoted by DRS, DCGS or QPC Services Company resources that are attributable to the entities, determined by reference to number of employees, salaries and wages and other similar measures for the relevant DRS, DCGS or QPC Services Company service. Management believes the assumptions and methodologies underlying the allocation of general corporate overhead expenses are reasonable.

Acquisitions

Acquisitions	3 Months Ended
	Mar. 31, 2017
Business Combinations [Abstract]
Acquisitions	Acquisitions Questar Pipeline In October 2016, Dominion Midstream, following approval by the Conflicts Committee of Dominion Midstream GP, LLC, its general partner, entered into the Questar Pipeline Contribution Agreement to acquire Questar Pipeline from Dominion. Upon closing of the agreement on December 1, 2016, Dominion Midstream became the owner of all of the issued and outstanding membership interests of Questar Pipeline in exchange for consideration consisting of: (1) 6,656,839 common units with a value of $167.3 million (the number of Dominion Midstream common units issued to Dominion was determined by the volume-weighted average trading price of Dominion Midstream's common units on the NYSE for the 10 -day trading period immediately preceding closing), (2) 11,365,628 Series A Preferred Units with a value of $300.0 million and (3) a cash payment of $822.7 million , $300.0 million of which is treated as a debt-financed distribution, for total consideration of $1.29 billion . In addition, Questar Pipeline's debt of $435.0 million remains outstanding. As a result of the transaction, Dominion Midstream owns 100% of the membership interests in Questar Pipeline and therefore consolidates Questar Pipeline in its financial statements. Because the contribution of Questar Pipeline by Dominion to Dominion Midstream is considered a reorganization of entities under common control, Questar Pipeline's assets and liabilities are recorded in Dominion Midstream's consolidated financial statements at Dominion’s historical cost of $989.3 million at December 1, 2016. Common control began on September 16, 2016, concurrent with Dominion's acquisition of Dominion Questar, which was accounted for using the acquisition method of accounting. Accordingly, the consolidated financial statements of Dominion Midstream reflect Questar Pipeline's financial results beginning September 16, 2016. The Questar Pipeline Acquisition supports the expansion of Dominion Midstream's portfolio of natural gas terminaling, processing, storage, transportation and related assets. To facilitate the financing of the acquisition of Questar Pipeline, Dominion Midstream completed a public issuance of 15,525,000 common units, which included a 2,025,000 common unit over-allotment option that was exercised in full by the underwriters, resulting in proceeds of $347.6 million , net of offering costs of $12.6 million , in November 2016. In addition, in December 2016, Dominion Midstream completed the private placement of 5,990,634 common units with a value of $137.5 million (determined by the price of the common units in the public offering discussed above, less $0.2475 in accordance with the Private Placement Agreement) and 18,942,714 Series A Preferred Units with a value of $500.0 million . Also in December 2016, Dominion Midstream entered into a $300.0 million three -year term loan agreement, which bears interest at a variable rate. The key terms of the term loan agreement are discussed in Note 15 to the Consolidated Financial Statements in Dominion Midstream's Annual Report on Form 10-K for the year ended December 31, 2016. Offering expenses associated with the private placement of common units ( $3.1 million ), Series A Preferred Units ( $9.9 million ) and the term loan agreement ( $1.5 million ) were funded through a draw on the existing revolving credit facility with Dominion. As a condition to closing under the Questar Pipeline Contribution Agreement, Dominion Midstream repaid the outstanding $300.8 million senior unsecured promissory note payable to Dominion and repurchased 6,656,839 common units from Dominion for $167.3 million (based on the volume-weighted average trading price of Dominion Midstream's common units on the NYSE for the 10 -day trading period immediately preceding closing) in December 2016. In connection with the private placement of common units and Series A Preferred Units, Dominion Midstream entered into a registration rights agreement under which Dominion Midstream is required to register (1) the common units by March 31, 2017, (2) common units issuable upon conversion of the Series A Preferred Units by December 1, 2018, and (3) the Series A Preferred Units no earlier than December 1, 2021 provided that the required amount of units remain outstanding. Dominion Midstream’s registration statement for the applicable common units became effective in February 2017. In connection with the Questar Pipeline Acquisition, transition costs of $0.2 million incurred by our general partner were expensed to operations and maintenance expense in the Consolidated Statements of Income for the three months ended March 31, 2017. These costs were paid by Dominion. Dominion did not seek reimbursement and accordingly, Dominion Midstream recognized an equity contribution from the general partner. Questar Pipeline owns and operates interstate natural gas pipelines and storage facilities in the western U.S. providing natural gas transportation and underground storage services in Utah, Wyoming and Colorado. Questar Pipeline's operations are primarily regulated by FERC. At December 31, 2016, Questar Pipeline owned and operated nearly 2,200 miles of natural gas transportation pipelines across northeastern and central Utah, northwestern Colorado and southwestern Wyoming and nearly 56 billion cubic feet of working gas storage capacity. Questar Pipeline's core transportation system is strategically located near large reserves of natural gas in six major Rocky Mountain producing areas. Questar Pipeline transports natural gas from these producing areas to other major pipeline systems, Questar Gas Company's distribution system and other utility systems. Questar Pipeline operates and owns 50% of White River Hub, an 11 -mile FERC-regulated natural gas transportation pipeline in western Colorado, which is accounted for under the equity method. Questar Pipeline also owns gathering lines and processing facilities in Utah, through which it provides gas-processing services.

Significant Accounting Policies

Significant Accounting Policies	3 Months Ended
	Mar. 31, 2017
Accounting Policies [Abstract]
Significant Accounting Policies	Significant Accounting Policies Interim Financial Information and Estimates As permitted by the rules and regulations of the SEC, Dominion Midstream's accompanying unaudited Consolidated Financial Statements exclude certain footnote disclosures normally included in annual audited consolidated financial statements prepared in accordance with GAAP. These unaudited Consolidated Financial Statements should be read in conjunction with the Consolidated Financial Statements and Notes in Dominion Midstream’s Annual Report on Form 10-K for the year ended December 31, 2016. In the opinion of management, the accompanying unaudited Consolidated Financial Statements contain all adjustments necessary to present fairly Dominion Midstream's financial position at March 31, 2017, its results of operations and cash flows for the three months ended March 31, 2017 and 2016, and changes in equity for the three months ended March 31, 2017. Such adjustments are normal and recurring in nature unless otherwise noted. Dominion Midstream makes certain estimates and assumptions in preparing its Consolidated Financial Statements in accordance with GAAP. These estimates and assumptions affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses for the periods presented. Actual results may differ from those estimates. The results of operations for interim periods are not necessarily indicative of the results expected for the full year. Information for quarterly periods is affected by seasonal variations in sales, rate changes, purchased gas expenses and other factors. Certain amounts in Dominion Midstream's 2016 audited Consolidated Financial Statements and Notes have been reclassified to conform to the 2017 presentation for comparative purposes. The reclassifications did not affect Dominion Midstream's net income, total assets, liabilities, equity or cash flows. With the exception of the items described below, there have been no significant changes from Note 3 to the Consolidated Financial Statements in Dominion Midstream's Annual Report on Form 10-K for the year ended December 31, 2016. Derivative Instruments Effective March 2017, Dominion Midstream uses derivative instruments such as swaps to manage interest rate risks of its business operations. All derivatives, except those for which an exception applies, are required to be reported in the Consolidated Balance Sheets at fair value. Derivative contracts representing unrealized gain positions are reported as derivative assets. Derivative contracts representing unrealized losses are reported as derivative liabilities. Dominion Midstream does not offset amounts recognized for the right to reclaim cash collateral or the obligation to return cash collateral against amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement. Dominion Midstream had no margin assets or liabilities associated with cash collateral at March 31, 2017. See Note 8 for further information about derivatives. Derivative Instruments Designated as Hedging Instruments Dominion Midstream has designated all of its derivative instruments as cash flow hedges for accounting purposes. For all derivatives designated as hedges, Dominion Midstream formally documents the relationship between the hedging instrument and the hedged item, as well as the risk management objective and the strategy for using the hedging instrument. Dominion Midstream assesses whether the hedging relationship between the derivative and the hedged item is highly effective at offsetting changes in cash flows both at the inception of the hedging relationship and on an ongoing basis. Any change in the fair value of the derivative that is not effective at offsetting changes in the cash flows of the hedged item is recognized currently in earnings. Hedge accounting is discontinued prospectively for derivatives that cease to be highly effective hedges. The cash flows from the cash flow hedge derivatives and from the related hedged items are classified in operating cash flows. Dominion Midstream uses interest rate swaps to hedge its exposure to the variability of cash flows as a result of the variable interest rates on long-term debt. Changes in the fair value of the derivatives are reported in AOCI, to the extent they are effective at offsetting changes in the hedged item. Any derivative gains or losses reported in AOCI are reclassified to earnings when the forecasted item is included in earnings, or earlier, if it becomes probable that the forecasted transaction will not occur. Hedge accounting is discontinued if the occurrence of the forecasted transaction is no longer probable.

Net Income Per Limited Partner

Net Income Per Limited Partner Unit	3 Months Ended
	Mar. 31, 2017
Earnings Per Share [Abstract]
Net Income Per Limited Partner Unit	Net Income Per Limited Partner Unit Basic net income per limited partner unit applicable to common and subordinated units is computed by dividing the respective limited partners’ interest in net income attributable to Dominion Midstream, after deducting any net income attributable to Series A Preferred Units and incentive distributions, by the weighted average number of common units and subordinated units outstanding. Because Dominion Midstream has more than one class of participating securities, the two-class method is used when calculating the net income per unit applicable to limited partners. The classes of participating securities include common units, subordinated units, Series A Preferred Units and IDRs. See Note 2 to the Consolidated Financial Statements in Dominion Midstream's Annual Report on Form 10-K for the year ended December 31, 2016 for further information about the Series A Preferred Units. Dominion Midstream’s net income is allocated to the limited partners in accordance with their respective partnership interests, after giving effect to priority income allocations to the holders of the Series A Preferred Units and incentive distributions, if any, to Dominion, the holder of the IDRs, pursuant to the partnership agreement. The distributions are declared and paid following the close of each quarter. Earnings in excess of distributions are allocated to the common and subordinated unitholders based on their respective ownership interests. Payments made to Dominion Midstream's unitholders are determined in relation to actual distributions declared and are not based on the net income allocations used in the calculation of earnings per limited partner unit. Diluted net income per limited partner unit reflects the potential dilution that could occur if securities or agreements to issue common units, such as the Series A Preferred Units, were converted into common units. When it is determined that potential common units resulting from the Series A Preferred Unit conversion should be included in the diluted net income per limited partner unit calculation, the impact is calculated using the two class method. There were no potentially dilutive common units outstanding at March 31, 2016. Basic and diluted earnings per unit applicable to subordinated limited partnerships are the same because there are no potentially dilutive subordinated units outstanding. The calculation of net income per limited partner unit is as follows: Three Months Ended March 31, 2017 2016 (millions) Net income attributable to partners $ 52.2 $ 23.1 Less: General partner allocation (1) (0.2 ) — Less: Preferred unitholder allocation 9.5 — Distributions declared on: IDRs (2) 2.9 0.4 Common unitholders 18.4 10.3 Subordinated unitholder 8.8 7.1 Total distributions declared 30.1 17.8 Undistributed earnings $ 12.8 $ 5.3 (1) See Note 2 for further information. (2) Dominion is a non-economic general partner that holds all of the IDRs. Distributions are declared and paid subsequent to quarter end. The table below summarizes the quarterly distributions on common and subordinated units related to the first quarter of 2017 and 2016. Quarterly Period Ended Total Quarterly Distribution (per unit) Total Cash Distribution (in millions) Date of Declaration Date of Record Date of Distribution December 31, 2015 $ 0.2135 $ 16.8 January 21, 2016 February 5, 2016 February 15, 2016 March 31, 2016 0.2245 17.8 April 19, 2016 May 3, 2016 May 13, 2016 December 31, 2016 0.2605 27.5 January 25, 2017 February 6, 2017 February 15, 2017 March 31, 2017 0.2740 30.1 April 21, 2017 May 5, 2017 May 15, 2017 Record holders of the Series A Preferred Units are entitled to receive cumulative quarterly distributions, payable in cash, payable in kind or a combination thereof at the option of our general partner, equal to $0.3134 in respect of each quarter ending before December 1, 2018. The table below summarizes the quarterly distributions on the Series A Preferred Units related to the first quarter of 2017. Quarterly Period Ended Total Distribution (in millions) Amount Payable in Cash (in millions) Amount Payable in Kind (in millions) December 31, 2016 $ 3.2 (1) $ 3.2 $ — March 31, 2017 9.5 9.5 — (1) For the period subsequent to the issuance of the Series A Preferred Units through December 31, 2016, the initial quarterly cash distribution was calculated as the minimum quarterly distribution of $0.3134 per unit prorated for the portion of the quarter subsequent to the issuance of the Series A Preferred Units. Basic and diluted net income per limited partner unit for the three months ended March 31, 2017 are as follows: Common Units Subordinated Units Series A Preferred Units General Partner (including IDRs) Total (millions, except for weighted average units and per unit data) Three Months Ended March 31, 2017 General partner allocation $ — $ — $ — $ (0.2 ) $ (0.2 ) Preferred unitholder allocation — — 9.5 — 9.5 Distributions declared 18.4 8.8 — 2.9 30.1 Undistributed earnings 8.7 4.1 — — 12.8 Net income attributable to partners (basic) $ 27.1 $ 12.9 $ 9.5 $ 2.7 $ 52.2 Dilutive effect of Series A Preferred Units (1) 9.5 — Net income attributable to partners (diluted) 36.6 12.9 Weighted average units outstanding (basic) 67,239,779 31,972,789 Dilutive effect of Series A Preferred Units (1) 30,308,342 — Weighted average units outstanding (diluted) 97,548,121 31,972,789 Net income per limited partner unit (basic) $ 0.40 $ 0.40 Net income per limited partner unit (diluted) $ 0.37 $ 0.40 (1) The dilutive effect of the Series A Preferred Units represents the reallocation of net income to limited partners including a reallocation of IDRs pursuant to the partnership agreement assuming conversion of the Series A Preferred Units into common units at the beginning of the period. Basic and diluted net income per limited partner unit for the three months ended March 31, 2016 are as follows: Common Units Subordinated Units General Partner (including IDRs) Total (millions, except for weighted average units and per unit data) Three Months Ended March 31, 2016 Distributions declared $ 10.3 $ 7.1 $ 0.4 $ 17.8 Undistributed earnings 3.1 2.2 — 5.3 Net income attributable to partners (basic and diluted) $ 13.4 $ 9.3 $ 0.4 $ 23.1 Weighted average units outstanding 45,722,112 31,972,789 Net income per limited partner unit (basic and diluted) $ 0.29 $ 0.29

Unit Activity

Unit Activity	3 Months Ended
	Mar. 31, 2017
Equity [Abstract]
Unit Activity	Unit Activity Activity in number of units was as follows: Convertible Preferred Common Public Dominion Public Dominion Subordinated General Partner Total (non-economic interest) Balance at December 31, 2015 — — 27,867,938 17,846,672 31,972,789 — 77,687,399 Unit-based compensation — — 7,761 — — — 7,761 Dominion purchase of common units (1) — — (377,311 ) 377,311 — — — Balance at March 31, 2016 — — 27,498,388 18,223,983 31,972,789 — 77,695,160 Balance at December 31, 2016 18,942,714 11,365,628 48,734,195 18,504,628 31,972,789 — 129,519,954 Unit-based compensation — — 10,444 — — — 10,444 Balance at March 31, 2017 18,942,714 11,365,628 48,744,639 18,504,628 31,972,789 — 129,530,398 (1) These units were purchased by Dominion as part of Dominion's program initiated in September 2015, which expired in September 2016, to purchase from the market up to $50.0 million of common units representing limited partner interests in Dominion Midstream at the discretion of Dominion's management.

Operating Revenue

Operating Revenue	3 Months Ended
	Mar. 31, 2017
Revenue Recognition [Abstract]
Operating Revenue	Operating Revenue Dominion Midstream's operating revenue consists of the following: Three Months Ended March 31, 2017 2016 (millions) Gas transportation and storage $ 124.6 $ 79.1 Regulated gas sales 0.3 — Other 5.3 3.9 Total operating revenue $ 130.2 $ 83.0

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (exit price) in an orderly transaction between market participants at the measurement date. However, the use of a mid-market pricing convention (the mid-point between bid and ask prices) is permitted. Fair values are based on assumptions that market participants would use when pricing an asset or liability, including assumptions about risk and the risks inherent in valuation techniques and the inputs to valuations. This includes not only the credit standing of counterparties involved and the impact of credit enhancements but also the impact of Dominion Midstream's own nonperformance risk on its liabilities. Fair value measurements assume that the transaction occurs in the principal market for the asset or liability (the market with the most volume and activity for the asset or liability from the perspective of the reporting entity), or in the absence of a principal market, the most advantageous market for the asset or liability (the market in which the reporting entity would be able to maximize the amount received or minimize the amount paid). Dominion Midstream applies fair value measurements to assets and liabilities associated with interest rate derivative instruments in accordance with the requirements discussed above. Credit adjustments are not considered material to the interest rate derivative fair values. Inputs and Assumptions Dominion Midstream maximizes the use of observable inputs and minimizes the use of unobservable inputs when measuring fair value. Fair value is based on actively-quoted market prices, if available. In the absence of actively-quoted market prices, price information is sought from external sources, including broker quotes and industry publications. When evaluating pricing information provided by brokers and other pricing services, Dominion Midstream considers whether the broker is willing and able to trade at the quoted price, if the broker quotes are based on an active market or an inactive market and the extent to which brokers are utilizing a particular model if pricing is not readily available. If pricing information from external sources is not available, or if Dominion Midstream believes that observable pricing is not indicative of fair value, judgment is required to develop the estimates of fair value. In those cases, Dominion Midstream must estimate prices based on available historical and near-term future price information that reflect its market assumptions. The inputs and assumptions used in measuring fair value for interest rate derivative contracts include the following: • Interest rate curves • Credit quality of counterparties and Dominion Midstream • Notional value • Credit enhancements • Time value Levels Dominion Midstream also utilizes the following fair value hierarchy, which prioritizes the inputs to valuation techniques used to measure fair value into three broad levels: • Level 1-Quoted prices (unadjusted) in active markets for identical assets and liabilities that it has the ability to access at the measurement date. • Level 2-Inputs other than quoted prices included within Level 1 that are either directly or indirectly observable for the asset or liability, including quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in inactive markets, inputs other than quoted prices that are observable for the asset or liability, and inputs that are derived from observable market data by correlation or other means. Instruments categorized in Level 2 include interest rate swaps. • Level 3-Unobservable inputs for the asset or liability, including situations where there is little, if any, market activity for the asset or liability. The fair value hierarchy gives the highest priority to quoted prices in active markets (Level 1) and the lowest priority to unobservable data (Level 3). In some cases, the inputs used to measure fair value might fall in different levels of the fair value hierarchy. In these cases, the lowest level input that is significant to a fair value measurement in its entirety determines the applicable level in the fair value hierarchy. Assessing the significance of a particular input to the fair value measurement in its entirety requires judgment, considering factors specific to the asset or liability. For derivative contracts, Dominion Midstream recognizes transfers among Level 1, Level 2 and Level 3 based on fair values as of the first day of the month in which the transfer occurs. Transfers out of Level 3 represent assets and liabilities that were previously classified as Level 3 for which the inputs became observable for classification in either Level 1 or Level 2. Dominion Midstream did not have any Level 3 derivative contracts as of March 31, 2017. Recurring Fair Value Measurements Fair value measurements are separately disclosed by level within the fair value hierarchy. The following table presents Dominion Midstream's assets and liabilities that are measured at fair value on a recurring basis for each hierarchy level, including both current and noncurrent portions. There were no assets or liabilities measured at fair value at December 31, 2016. Level 1 Level 2 Level 3 Total (millions) At March 31, 2017 Assets Interest rate derivative $ — $ 0.7 $ — $ 0.7 Total assets $ — $ 0.7 $ — $ 0.7 Liabilities Interest rate derivative $ — $ 1.2 $ — $ 1.2 Total liabilities $ — $ 1.2 $ — $ 1.2 Fair Value of Financial Instruments Substantially all of Dominion Midstream's financial instruments are recorded at fair value, with the exception of the instruments described below, which are reported at historical cost. Estimated fair values have been determined using available market information and valuation methodologies considered appropriate by management. The carrying amount of cash and cash equivalents, restricted cash, customer and other receivables, affiliated receivables, Dominion credit facility borrowings, payables to affiliates and accounts payable are representative of fair value because of the short-term nature of these instruments. For Dominion Midstream's financial instruments that are not recorded at fair value, the carrying amounts and estimated fair values are as follows: March 31, 2017 December 31, 2016 Carrying Estimated Fair (1) Carrying Estimated Fair (1) (millions) Long-term debt, including securities due within one year (2) $ 729.8 $ 749.8 $ 729.9 $ 744.8 (1) Fair value is estimated using market prices, where available, and interest rates currently available for issuance of debt with similar terms and remaining maturities. All fair value measurements are classified as Level 2. The carrying amount of debt issues with short-term maturities and variable rates refinanced at current market rates is a reasonable estimate of their fair value. (2) Carrying amount includes amounts which represent the unamortized debt issuance costs, discount or premium.

Derivatives and Hedge Accountin

Derivatives and Hedge Accounting Activities	3 Months Ended
	Mar. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives and Hedge Accounting Activities	Derivatives and Hedge Accounting Activities Dominion Midstream is exposed to the impact of market fluctuations in interest rate risks of its business operations. Dominion Midstream uses derivative instruments to manage exposure to this risk, and has designated all of its derivative instruments as cash flow hedges for accounting purposes. See Note 7 for further information about fair value measurements and associated valuation methods for derivatives. Derivative assets and liabilities are presented gross on Dominion Midstream's Consolidated Balance Sheets. Dominion Midstream's derivative contracts include over-the-counter transactions. Over-the-counter contracts are bilateral contracts that are transacted directly with a third party. Certain over-the-counter contracts contain contractual rights of setoff through master netting arrangements, derivative clearing agreements, and contract default provisions. In addition, the contracts are subject to conditional rights of setoff through counterparty nonperformance, insolvency, or other conditions. Balance Sheet Presentation The tables below present Dominion Midstream's derivative asset and liability balances by type of financial instrument, before and after the effects of offsetting. There were no derivative asset or liability balances at December 31, 2016. March 31, 2017 Gross Amounts of Recognized Assets Gross Amounts Offset in the Consolidated Balance Sheet Net Amounts of Assets Presented in the Consolidated Balance Sheet (millions) Interest rate contracts: Over-the-counter $ 0.7 $ — $ 0.7 Total derivatives, subject to a master netting or similar arrangement 0.7 — 0.7 Total derivatives, not subject to a master netting or similar arrangement — — — Total $ 0.7 $ — $ 0.7 March 31, 2017 Gross Amounts Not Offset in the Consolidated Balance Sheet Net Amounts of Assets Presented in the Consolidated Balance Sheet Financial Instruments Cash Collateral Received Net Amounts (millions) Interest rate contracts: Over-the-counter $ 0.7 $ 0.7 $ — $ — Total $ 0.7 $ 0.7 $ — $ — March 31, 2017 Gross Amounts of Recognized Liabilities Gross Amounts Offset in the Consolidated Balance Sheet Net Amounts of Liabilities Presented in the Consolidated Balance Sheet (millions) Interest rate contracts: Over-the-counter $ 1.2 $ — $ 1.2 Total derivatives, subject to a master netting or similar arrangement 1.2 — 1.2 Total derivatives, not subject to a master netting or similar arrangement — — — Total $ 1.2 $ — $ 1.2 March 31, 2017 Gross Amounts Not Offset in the Consolidated Balance Sheet Net Amounts of Liabilities Presented in the Consolidated Balance Sheet Financial Instruments Cash Collateral Paid Net Amounts (millions) Interest rate contracts: Over-the-counter $ 1.2 $ 0.7 $ — $ 0.5 Total $ 1.2 $ 0.7 $ — $ 0.5 Volumes The following table presents the volume of Dominion Midstream’s derivative activity at March 31, 2017. These volumes are based on open derivative positions and represent the combined absolute value of their long and short positions, except in the case of offsetting transactions, for which they represent the absolute value of the net volume of their long and short positions. Current Noncurrent Interest rate (1) $ — $ 300,000,000 (1) Maturity is determined based on final settlement period. Ineffectiveness and AOCI For the three months ended March 31, 2017, there were no gains or losses on hedging instruments determined to be ineffective and amounts excluded from the assessment of effectiveness. The following table presents selected information related to gains (losses) on cash flow hedges included in AOCI in Dominion Midstream's Consolidated Balance Sheet at March 31, 2017: AOCI Amounts Expected to be Reclassified to Earnings During the Next 12 Months Maximum Term (millions) Interest rate $ (0.5 ) $ (1.2 ) 32 months Total $ (0.5 ) $ (1.2 ) The amounts that will be reclassified from AOCI to earnings will generally be offset by the recognition of the hedged transactions (e.g., interest payments) in earnings, thereby achieving the realization of prices contemplated by the underlying risk management strategies and will vary from the expected amounts presented above as a result of changes in interest rates. Fair Value and Gains and Losses on Derivative Instruments The following tables present the fair values of Dominion Midstream's derivatives and where they are presented in its Consolidated Balance Sheets. Dominion Midstream did not have any derivatives at December 31, 2016. Fair Value – Total Fair Value (millions) At March 31, 2017 ASSETS Noncurrent Assets Interest rate $ 0.7 $ 0.7 Total noncurrent derivative assets (1) 0.7 0.7 Total derivative assets $ 0.7 $ 0.7 LIABILITIES Current Liabilities Interest rate $ 1.2 $ 1.2 Total current derivative liabilities (2) 1.2 1.2 Total derivative liabilities $ 1.2 $ 1.2 (1) Noncurrent derivative assets are presented in other deferred charges and other assets in Dominion Midstream's Consolidated Balance Sheets. (2) Current derivative liabilities are presented in other current liabilities in Dominion Midstream's Consolidated Balance Sheets. The following tables present the gains and losses on Dominion Midstream's derivatives, as well as where the associated activity is presented in its Consolidated Balance Sheets and Statements of Income. Dominion Midstream did not have any derivatives during the three months ended March 31, 2016. Derivatives in Cash Flow Hedging Relationships Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective (1) Amount of Gain (millions) Three Months Ended March 31, 2017 Derivative type and location of gains (losses): Interest rate (2) $ (0.5 ) $ — Total $ (0.5 ) $ — (1) Amounts deferred into AOCI have no associated effect in Dominion Midstream's Consolidated Statements of Income. (2) Amounts recorded in Dominion Midstream's Consolidated Statements of Income are classified in interest and related charges.

Equity Method Investments

Equity Method Investments	3 Months Ended
	Mar. 31, 2017
Equity Method Investments and Joint Ventures [Abstract]
Equity Method Investments	Equity Method Investments At March 31, 2017, Dominion Midstream used the equity method to account for its 25.93% noncontrolling partnership interest in Iroquois and its 50% noncontrolling partnership interest in White River Hub. See further discussion of Iroquois and White River Hub in Note 8 to the Consolidated Financial Statements in Dominion Midstream’s Annual Report on Form 10-K for the year ended December 31, 2016. The table below summarizes distributions received and income earned from Dominion Midstream's equity method investees for the three months ended March 31, 2017 and 2016. (in millions) Iroquois White River Hub Three Months Ended March 31, 2017 Distributions received $ 5.8 $ 1.2 Income from equity method investees 7.1 0.9 Three Months Ended March 31, 2016 Distributions received $ 5.8 Income from equity method investees 6.4 The table below summarizes the carrying amount of the investments and excess of investment over Dominion Midstream's share of underlying equity in net assets at March 31, 2017 and December 31, 2016. (in millions) Iroquois White River Hub March 31, 2017 December 31, 2016 March 31, 2017 December 31, 2016 Carrying amount of investment $ 219.9 $ 218.7 $ 38.9 $ 39.1 Excess of investment over Dominion Midstream's share of underlying equity in net assets (1) 122.9 122.9 16.1 16.1 (1) The difference between the carrying value of Dominion Midstream's equity method investments and its share in the underlying equity in net assets reflects equity method goodwill and is not being amortized. Summarized financial information provided to us by Iroquois for 100% of Iroquois for the three months ended March 31, 2017 and 2016 is presented below. Three Months Ended March 31, (in millions) 2017 2016 Revenues $ 53.3 $ 53.0 Operating income 31.9 28.8 Net income 26.5 24.6 Summarized financial information provided to us by White River Hub for 100% of White River Hub for the three months ended March 31, 2017 is presented below. Three Months Ended (in millions) March 31, 2017 Revenues $ 2.6 Operating income 1.8 Net income 1.8

Regulatory Assets and Liabiliti

Regulatory Assets and Liabilities	3 Months Ended
	Mar. 31, 2017
Regulated Operations [Abstract]
Regulatory Assets and Liabilities	Regulatory Assets and Liabilities Regulatory assets and liabilities include the following: March 31, 2017 December 31, 2016 (millions) Regulatory assets: Unrecovered gas costs (1) $ 4.5 $ 3.3 Interest rate hedges (2) 0.6 0.6 Other 0.9 1.2 Regulatory assets-current 6.0 5.1 Income taxes recoverable through future rates (3) 4.1 3.6 Interest rate hedges (2) 33.8 34.0 Cost of reacquired debt (4) 1.4 1.5 Other 1.3 1.1 Regulatory assets-noncurrent 40.6 40.2 Total regulatory assets $ 46.6 $ 45.3 Regulatory liabilities: Overrecovered gas costs (1) $ 0.7 $ 0.4 LNG cargo obligations (5) 2.6 3.2 Customer bankruptcy settlement (6) 2.8 2.8 Other 1.9 1.1 Regulatory liabilities-current 8.0 7.5 Provision for future cost of removal and AROs (7) 101.5 100.0 Unrecognized other postretirement benefit costs (8) 12.0 11.1 Customer bankruptcy settlement (6) 16.9 17.6 Other 0.3 0.4 Regulatory liabilities-noncurrent 130.7 129.1 Total regulatory liabilities $ 138.7 $ 136.6 (1) Reflects unrecovered/overrecovered gas costs, which are subject to annual filings with FERC. (2) Reflects interest rate cash flow hedges recoverable from customers. Questar Pipeline entered into forward starting swaps totaling $150.0 million in the second and third quarters of 2011 in anticipation of issuing $180.0 million of notes in December 2011. Settlement of these swaps required payments of $37.3 million in the fourth quarter of 2011 because of declines in interest rates. These swaps qualified as cash flow hedges and the settlement payments are being amortized to interest expense over the 30 -year life of the debt. (3) Amounts to be recovered through future rates to pay income taxes that become payable by unitholders when rate revenue is provided to recover AFUDC equity when such amounts are recovered through book depreciation. (4) Represents charges incurred on the reacquisition of debt by Questar Pipeline that are deferred and amortized as interest expense over the would-be remaining life of the reacquired debt. The reacquired debt costs had a weighted-average life of approximately 3.7 years at March 31, 2017. (5) Reflects obligations to the Import Shippers for LNG cargo received. See Note 12 to the Consolidated Financial Statements in Dominion Midstream's Annual Report on Form 10-K for the year ended December 31, 2016 for further information. (6) Represents the balance of proceeds from the monetization of a bankruptcy claim acquired as part of the DCG Acquisition, which is being amortized into operating revenue through February 2024. (7) Rates charged to customers include a provision for the cost of future activities to remove assets that are expected to be incurred at the time of retirement. (8) Reflects a regulatory liability for the collection of postretirement medical costs allowed in rates in excess of expenses incurred at Questar Pipeline. At March 31, 2017, approximately $40.7 million of regulatory assets represented past expenditures on which Dominion Midstream does not currently earn a return. With the exception of regulatory assets related to interest rate hedges, these expenditures are expected to be recovered within two years.

Regulatory Matters

Regulatory Matters	3 Months Ended
	Mar. 31, 2017
Regulated Operations [Abstract]
Regulatory Matters	Regulatory Matters FERC regulates the transportation and sale for resale of natural gas in interstate commerce under the NGA and the Natural Gas Policy Act of 1978, as amended. Under the NGA, FERC has authority over rates, terms and conditions of services performed by Cove Point, DCG and Questar Pipeline. FERC also has jurisdiction over siting, construction and operation of natural gas import and export facilities and interstate natural gas pipeline facilities. There have been no significant developments regarding the pending regulatory matters disclosed in Note 12 to the Consolidated Financial Statements in Dominion Midstream’s Annual Report on Form 10-K for the year ended December 31, 2016.

Variable Interest Entities

Variable Interest Entities	3 Months Ended
	Mar. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Variable Interest Entities	Variable Interest Entities There have been no significant changes regarding the entities Dominion Midstream considers VIEs as described in Note 14 to the Consolidated Financial Statements in Dominion Midstream's Annual Report on Form 10-K for the year ended December 31, 2016. Dominion Midstream reimburses its general partner and affiliates for the costs of providing administrative, management and other services necessary for its operations. For the three months ended March 31, 2017 and 2016, these costs were $0.4 million and $0.3 million , respectively. In addition to the services purchased by our general partner, Dominion Midstream purchased shared services from DRS, DCGS and QPC Services Company of approximately $6.9 million , $3.2 million and $6.9 million , respectively, for the three months ended March 31, 2017. Dominion Midstream purchased shared services from DRS and DCGS of approximately $6.7 million and $5.0 million for the three months ended March 31, 2016, respectively. The Consolidated Balance Sheets at March 31, 2017 and December 31, 2016 include amounts due from Dominion Midstream to DRS, DCGS and QPC Services Company of approximately $4.4 million and $6.3 million , respectively. The Consolidated Balance Sheet at March 31, 2017 includes amounts due to Dominion Midstream from DRS of $0.4 million . There were no such amounts due to Dominion Midstream at December 31, 2016.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies As a result of issues generated in the ordinary course of business, Dominion Midstream is involved in legal proceedings before various courts and is periodically subject to governmental examinations (including by FERC), inquiries and investigations. Certain legal proceedings and governmental examinations involve demands for unspecified amounts of damages, are in an initial procedural phase, involve uncertainty as to the outcome of pending appeals or motions, or involve significant factual issues that need to be resolved, such that it is not possible for Dominion Midstream to estimate a range of possible loss. For such matters that Dominion Midstream cannot estimate, a statement to this effect is made in the description of the matter. Other matters may have progressed sufficiently through the litigation or investigative processes such that Dominion Midstream is able to estimate a range of possible loss. For legal proceedings and governmental examinations for which Dominion Midstream is able to reasonably estimate a range of possible losses, an estimated range of possible loss is provided, in excess of the accrued liability (if any) for such matters. Estimated ranges of loss are inclusive of legal fees and net of any anticipated insurance recoveries. Any estimated range is based on currently available information and involves elements of judgment and significant uncertainties. Any accrued liability is recorded on a gross basis with a receivable also recorded for any probable insurance recoveries. Any estimated range of possible loss may not represent Dominion Midstream’s maximum possible loss exposure. The circumstances of such legal proceedings and governmental examinations will change from time to time and actual results may vary significantly from the current estimate. Management does not anticipate that the liabilities, if any, arising from such proceedings would have a material effect on Dominion Midstream’s financial position, liquidity or results of operations. Cove Point Natural Heritage Trust Under the terms of the 2005 Agreement, Cove Point is required to make an annual contribution to the Cove Point Natural Heritage Trust, an affiliated non-profit trust focused on the preservation and protection of ecologically sensitive sites at or near Cove Point, of $0.3 million for each year the facility is in operation. These annual payments are recorded in other operations and maintenance expense in the Consolidated Statements of Income. If Cove Point voluntarily tenders title according to the terms of this agreement, no contributions are required. There are no current plans to voluntarily tender title to the Cove Point site. Surety Bonds At March 31, 2017, Dominion Midstream had purchased $13.1 million of surety bonds, including $9.8 million held by Cove Point. Under the terms of surety bonds, Dominion Midstream is obligated to indemnify the respective surety bond company for any amounts paid.

Credit Risk

Credit Risk	3 Months Ended
	Mar. 31, 2017
Risks and Uncertainties [Abstract]
Credit Risk	Credit Risk Credit risk is the risk of financial loss if counterparties fail to perform their contractual obligations. In order to minimize overall credit risk, credit policies are maintained, including the evaluation of counterparty financial condition. In addition, counterparties may make available collateral, including letters of credit, payment guarantees or cash deposits. Dominion Midstream provides service to approximately 130 customers, including the Storage Customers, marketers or end users, power generators, utilities and the Import Shippers. The three largest customers comprised approximately 42% of the total transportation and storage revenues for the three months ended March 31, 2017, with Dominion Midstream's largest customer, an affiliate, representing approximately 16% of such amounts during the period. The two largest customers comprised approximately 72% of the total transportation and storage revenues for the three months ended March 31, 2016, with Dominion Midstream's largest customer representing approximately 56% of such amounts during the period. Dominion Midstream maintains a provision for credit losses based on factors surrounding the credit risk of its customers, historical trends and other information. At March 31, 2017 and December 31, 2016, the provision for credit losses was less than $0.1 million . Management believes, based on credit policies and the March 31, 2017 provision for credit losses, that it is unlikely that a material adverse effect on financial position, results of operations or cash flows would occur as a result of counterparty nonperformance.

Related-Party Transactions

Related-Party Transactions	3 Months Ended
	Mar. 31, 2017
Related Party Transactions [Abstract]
Related-Party Transactions	Related-Party Transactions Dominion Midstream engages in related-party transactions primarily with other Dominion subsidiaries (affiliates), including our general partner. Dominion Midstream's receivable and payable balances with affiliates are settled based on contractual terms or on a monthly basis, depending on the nature of the underlying transactions. Cove Point participates in certain Dominion benefit plans as described in Note 16 to the Consolidated Financial Statements in Dominion Midstream's Annual Report on Form 10-K for the year ended December 31, 2016. In Dominion Midstream's Consolidated Balance Sheets at March 31, 2017 and December 31, 2016, amounts due to Dominion associated with these benefit plans included in other deferred credits and other liabilities were $6.7 million and $6.2 million , respectively, and amounts due from Dominion at March 31, 2017 and December 31, 2016 included in other deferred charges and other assets were $1.3 million and $0.9 million , respectively. Transactions related to the Questar Pipeline Acquisition are described in Note 2. A discussion of the remaining significant related party transactions follows. Transactions with Affiliates DRS provides accounting, legal, finance and certain administrative and technical services to Dominion Midstream and DCGS and QPC Services Company provide human resources and operations services to Dominion Midstream. Refer to Note 12 for further information. Dominion may seek reimbursement from DCG for costs incurred related to Dominion's transition services agreement with SCANA to provide administrative functions related to DCG. For the three months ended March 31, 2016, DCG reimbursed Dominion a total of $0.6 million for such costs. No such costs were incurred for the three months ended March 31, 2017. Dominion Midstream provides transportation and other services to affiliates and affiliates provide goods and services to Dominion Midstream. Affiliated transactions are presented below: Three Months Ended March 31, 2017 2016 (millions) Sales of natural gas transportation services to affiliates $ 22.6 $ 0.5 Services provided to affiliates 0.6 — Purchased gas from affiliates 2.5 0.1 Goods and services provided by affiliates to Dominion Midstream (1) 22.5 13.3 (1) Includes $6.9 million and $3.9 million of capitalized expenditures for the three months ended March 31, 2017 and 2016, respectively. Dominion Credit Facility In connection with the Offering, Dominion Midstream entered into a credit facility with Dominion with a borrowing capacity of $300.0 million . A summary of certain key terms of the credit facility with Dominion is included in Note 20 to the Consolidated Financial Statements in Dominion Midstream's Annual Report on Form 10-K for the year ended December 31, 2016. At March 31, 2017 and December 31, 2016, $67.9 million and $63.2 million was outstanding against the credit facility, respectively. In April 2017, Dominion Midstream drew an additional $6.9 million on the credit facility to fund expansion capital expenditures at DCG. Outstanding borrowings are presented within current liabilities as such amounts could become payable on demand after a 90 -day termination notice provided by either party. No such notice has been provided through the date of this filing. Interest charges related to Dominion Midstream's borrowings against the facility were $0.4 million and less than $0.1 million for the three months ended March 31, 2017 and 2016, respectively. Affiliated Long-Term Debt As a condition to closing under the Questar Pipeline Contribution Agreement, in December 2016 Dominion Midstream repaid a two -year, $300.8 million senior unsecured promissory note payable to Dominion, which was issued in connection with the DCG Acquisition. Interest charges related to Dominion Midstream's borrowing from Dominion were $0.5 million for the three months ended March 31, 2016. Natural Gas Imbalances Dominion Midstream maintains natural gas imbalances with affiliates. The imbalances with affiliates are provided below: March 31, 2017 December 31, 2016 (millions) Imbalances payable to affiliates (1) $ 2.2 $ 0.1 Imbalances receivable from affiliates (2) — 6.3 (1) Recorded in other current liabilities in the Consolidated Balance Sheets. (2) Recorded in other current assets in the Consolidated Balance Sheets. Right of First Offer In connection with the Offering, Dominion Midstream entered into a right of first offer agreement with Dominion as described in Note 20 to the Consolidated Financial Statements in Dominion Midstream's Annual Report on Form 10-K for the year ended December 31, 2016. There have been no changes to this agreement. Contributions from Dominion For the three months ended March 31, 2017 and 2016, Dominion contributed $329.2 million and $244.9 million , respectively, to Cove Point. In April 2017, Dominion contributed an additional $45.7 million to Cove Point. These contributions from Dominion to Cove Point represent funding for capital expenditures primarily related to the Liquefaction Project. For the three months ended March 31, 2017, Dominion allocated costs of $0.2 million to Dominion Midstream related to the Questar Pipeline Acquisition for which Dominion did not seek reimbursement.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Dominion Midstream is organized as an MLP, a pass-through entity for U.S. federal and state income tax purposes. Each unitholder is responsible for taking into account the unitholder’s respective share of Dominion Midstream’s items of taxable income, gain, loss and deduction in the preparation of income tax returns. Accordingly, Dominion Midstream's Consolidated Financial Statements do not include income taxes for the periods presented. See Note 21 to the Consolidated Financial Statements in Dominion Midstream's Annual Report on Form 10-K for the year ended December 31, 2016 for additional information.

Operating Segment

Operating Segment	3 Months Ended
	Mar. 31, 2017
Segment Reporting [Abstract]
Operating Segment	Operating Segment Dominion Midstream is organized primarily on the basis of products and services sold in the U.S. Dominion Energy, Dominion Midstream's operating segment, consists of gas transportation, LNG import and storage. Dominion Midstream also reports a Corporate and Other segment. The Corporate and Other segment primarily includes items attributable to Dominion Midstream's operating segment that are not included in profit measures evaluated by executive management in assessing the segment's performance or in allocating resources. The following table presents segment information pertaining to Dominion Midstream's operations: Dominion Energy Corporate and Other Total (millions) Three Months Ended March 31, 2017 Operating revenue $ 130.2 $ — $ 130.2 Earnings from equity method investees 8.0 — 8.0 Net income (loss) including noncontrolling interest and predecessors 54.5 (0.2 ) 54.3 Net income (loss) attributable to partners 52.4 (0.2 ) 52.2 Three Months Ended March 31, 2016 Operating revenue $ 83.0 $ — $ 83.0 Earnings from equity method investees 6.4 — 6.4 Net income including noncontrolling interest and predecessors 51.8 — 51.8 Net income attributable to partners 23.1 — 23.1

Significant Accounting Polici25

Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The contribution by Dominion to Dominion Midstream of the general partner interest in Cove Point and a portion of the Preferred Equity Interest is considered to be a reorganization of entities under common control. As a result, Dominion Midstream’s basis is equal to Dominion’s cost basis in the general partner interest in Cove Point and a portion of the Preferred Equity Interest. As discussed in Note 14 to the Consolidated Financial Statements in Dominion Midstream’s Annual Report on Form 10-K for the year ended December 31, 2016, Dominion Midstream is the primary beneficiary of, and therefore consolidates, Cove Point. As such, Dominion Midstream’s investment in the Preferred Equity Interest and Cove Point's preferred equity interest are eliminated in consolidation. Dominion's retained common equity interest in Cove Point is reflected as noncontrolling interest. The Questar Pipeline Acquisition is considered to be a reorganization of entities under common control. As a result, Dominion Midstream’s basis in Questar Pipeline is equal to Dominion’s cost basis in the assets and liabilities of Questar Pipeline. On December 1, 2016, Questar Pipeline became a wholly-owned subsidiary of Dominion Midstream and is therefore consolidated by Dominion Midstream. The accompanying financial statements and related notes include the historical results and financial position of Questar Pipeline beginning September 16, 2016, the inception date of common control. The financial statements for all periods presented include costs for certain general, administrative and corporate expenses assigned by DRS, DCGS or QPC Services Company to Dominion Midstream on the basis of direct and allocated methods in accordance with Dominion Midstream's services agreements with DRS, DCGS and QPC Services Company. Where costs incurred cannot be determined by specific identification, the costs are allocated based on the proportional level of effort devoted by DRS, DCGS or QPC Services Company resources that are attributable to the entities, determined by reference to number of employees, salaries and wages and other similar measures for the relevant DRS, DCGS or QPC Services Company service. Management believes the assumptions and methodologies underlying the allocation of general corporate overhead expenses are reasonable.
Combination of Entities under Common Control	The Questar Pipeline Acquisition is considered to be a reorganization of entities under common control. As a result, Dominion Midstream’s basis in Questar Pipeline is equal to Dominion’s cost basis in the assets and liabilities of Questar Pipeline. On December 1, 2016, Questar Pipeline became a wholly-owned subsidiary of Dominion Midstream and is therefore consolidated by Dominion Midstream. The accompanying financial statements and related notes include the historical results and financial position of Questar Pipeline beginning September 16, 2016, the inception date of common control.
Basis of Accounting	As permitted by the rules and regulations of the SEC, Dominion Midstream's accompanying unaudited Consolidated Financial Statements exclude certain footnote disclosures normally included in annual audited consolidated financial statements prepared in accordance with GAAP. These unaudited Consolidated Financial Statements should be read in conjunction with the Consolidated Financial Statements and Notes in Dominion Midstream’s Annual Report on Form 10-K for the year ended December 31, 2016.
Estimates	Dominion Midstream makes certain estimates and assumptions in preparing its Consolidated Financial Statements in accordance with GAAP. These estimates and assumptions affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses for the periods presented. Actual results may differ from those estimates.
Reclassification	Certain amounts in Dominion Midstream's 2016 audited Consolidated Financial Statements and Notes have been reclassified to conform to the 2017 presentation for comparative purposes. The reclassifications did not affect Dominion Midstream's net income, total assets, liabilities, equity or cash flows.
Derivative Instruments	Derivative Instruments Effective March 2017, Dominion Midstream uses derivative instruments such as swaps to manage interest rate risks of its business operations. All derivatives, except those for which an exception applies, are required to be reported in the Consolidated Balance Sheets at fair value. Derivative contracts representing unrealized gain positions are reported as derivative assets. Derivative contracts representing unrealized losses are reported as derivative liabilities. Dominion Midstream does not offset amounts recognized for the right to reclaim cash collateral or the obligation to return cash collateral against amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement. Dominion Midstream had no margin assets or liabilities associated with cash collateral at March 31, 2017. See Note 8 for further information about derivatives. Derivative Instruments Designated as Hedging Instruments Dominion Midstream has designated all of its derivative instruments as cash flow hedges for accounting purposes. For all derivatives designated as hedges, Dominion Midstream formally documents the relationship between the hedging instrument and the hedged item, as well as the risk management objective and the strategy for using the hedging instrument. Dominion Midstream assesses whether the hedging relationship between the derivative and the hedged item is highly effective at offsetting changes in cash flows both at the inception of the hedging relationship and on an ongoing basis. Any change in the fair value of the derivative that is not effective at offsetting changes in the cash flows of the hedged item is recognized currently in earnings. Hedge accounting is discontinued prospectively for derivatives that cease to be highly effective hedges. The cash flows from the cash flow hedge derivatives and from the related hedged items are classified in operating cash flows. Dominion Midstream uses interest rate swaps to hedge its exposure to the variability of cash flows as a result of the variable interest rates on long-term debt. Changes in the fair value of the derivatives are reported in AOCI, to the extent they are effective at offsetting changes in the hedged item. Any derivative gains or losses reported in AOCI are reclassified to earnings when the forecasted item is included in earnings, or earlier, if it becomes probable that the forecasted transaction will not occur. Hedge accounting is discontinued if the occurrence of the forecasted transaction is no longer probable. Dominion Midstream is exposed to the impact of market fluctuations in interest rate risks of its business operations. Dominion Midstream uses derivative instruments to manage exposure to this risk, and has designated all of its derivative instruments as cash flow hedges for accounting purposes. See Note 7 for further information about fair value measurements and associated valuation methods for derivatives. Derivative assets and liabilities are presented gross on Dominion Midstream's Consolidated Balance Sheets. Dominion Midstream's derivative contracts include over-the-counter transactions. Over-the-counter contracts are bilateral contracts that are transacted directly with a third party. Certain over-the-counter contracts contain contractual rights of setoff through master netting arrangements, derivative clearing agreements, and contract default provisions. In addition, the contracts are subject to conditional rights of setoff through counterparty nonperformance, insolvency, or other conditions.
Fair Value Measurements	Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (exit price) in an orderly transaction between market participants at the measurement date. However, the use of a mid-market pricing convention (the mid-point between bid and ask prices) is permitted. Fair values are based on assumptions that market participants would use when pricing an asset or liability, including assumptions about risk and the risks inherent in valuation techniques and the inputs to valuations. This includes not only the credit standing of counterparties involved and the impact of credit enhancements but also the impact of Dominion Midstream's own nonperformance risk on its liabilities. Fair value measurements assume that the transaction occurs in the principal market for the asset or liability (the market with the most volume and activity for the asset or liability from the perspective of the reporting entity), or in the absence of a principal market, the most advantageous market for the asset or liability (the market in which the reporting entity would be able to maximize the amount received or minimize the amount paid). Dominion Midstream applies fair value measurements to assets and liabilities associated with interest rate derivative instruments in accordance with the requirements discussed above. Credit adjustments are not considered material to the interest rate derivative fair values. Inputs and Assumptions Dominion Midstream maximizes the use of observable inputs and minimizes the use of unobservable inputs when measuring fair value. Fair value is based on actively-quoted market prices, if available. In the absence of actively-quoted market prices, price information is sought from external sources, including broker quotes and industry publications. When evaluating pricing information provided by brokers and other pricing services, Dominion Midstream considers whether the broker is willing and able to trade at the quoted price, if the broker quotes are based on an active market or an inactive market and the extent to which brokers are utilizing a particular model if pricing is not readily available. If pricing information from external sources is not available, or if Dominion Midstream believes that observable pricing is not indicative of fair value, judgment is required to develop the estimates of fair value. In those cases, Dominion Midstream must estimate prices based on available historical and near-term future price information that reflect its market assumptions. The inputs and assumptions used in measuring fair value for interest rate derivative contracts include the following: • Interest rate curves • Credit quality of counterparties and Dominion Midstream • Notional value • Credit enhancements • Time value Levels Dominion Midstream also utilizes the following fair value hierarchy, which prioritizes the inputs to valuation techniques used to measure fair value into three broad levels: • Level 1-Quoted prices (unadjusted) in active markets for identical assets and liabilities that it has the ability to access at the measurement date. • Level 2-Inputs other than quoted prices included within Level 1 that are either directly or indirectly observable for the asset or liability, including quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in inactive markets, inputs other than quoted prices that are observable for the asset or liability, and inputs that are derived from observable market data by correlation or other means. Instruments categorized in Level 2 include interest rate swaps. • Level 3-Unobservable inputs for the asset or liability, including situations where there is little, if any, market activity for the asset or liability. The fair value hierarchy gives the highest priority to quoted prices in active markets (Level 1) and the lowest priority to unobservable data (Level 3). In some cases, the inputs used to measure fair value might fall in different levels of the fair value hierarchy. In these cases, the lowest level input that is significant to a fair value measurement in its entirety determines the applicable level in the fair value hierarchy. Assessing the significance of a particular input to the fair value measurement in its entirety requires judgment, considering factors specific to the asset or liability. For derivative contracts, Dominion Midstream recognizes transfers among Level 1, Level 2 and Level 3 based on fair values as of the first day of the month in which the transfer occurs. Transfers out of Level 3 represent assets and liabilities that were previously classified as Level 3 for which the inputs became observable for classification in either Level 1 or Level 2.
Commitments and Contingencies	As a result of issues generated in the ordinary course of business, Dominion Midstream is involved in legal proceedings before various courts and is periodically subject to governmental examinations (including by FERC), inquiries and investigations. Certain legal proceedings and governmental examinations involve demands for unspecified amounts of damages, are in an initial procedural phase, involve uncertainty as to the outcome of pending appeals or motions, or involve significant factual issues that need to be resolved, such that it is not possible for Dominion Midstream to estimate a range of possible loss. For such matters that Dominion Midstream cannot estimate, a statement to this effect is made in the description of the matter. Other matters may have progressed sufficiently through the litigation or investigative processes such that Dominion Midstream is able to estimate a range of possible loss. For legal proceedings and governmental examinations for which Dominion Midstream is able to reasonably estimate a range of possible losses, an estimated range of possible loss is provided, in excess of the accrued liability (if any) for such matters. Estimated ranges of loss are inclusive of legal fees and net of any anticipated insurance recoveries. Any estimated range is based on currently available information and involves elements of judgment and significant uncertainties. Any accrued liability is recorded on a gross basis with a receivable also recorded for any probable insurance recoveries. Any estimated range of possible loss may not represent Dominion Midstream’s maximum possible loss exposure. The circumstances of such legal proceedings and governmental examinations will change from time to time and actual results may vary significantly from the current estimate. Management does not anticipate that the liabilities, if any, arising from such proceedings would have a material effect on Dominion Midstream’s financial position, liquidity or results of operations.
Credit Risk	Credit risk is the risk of financial loss if counterparties fail to perform their contractual obligations. In order to minimize overall credit risk, credit policies are maintained, including the evaluation of counterparty financial condition. In addition, counterparties may make available collateral, including letters of credit, payment guarantees or cash deposits.

Net Income Per Limited Partne26

Net Income Per Limited Partner Unit (Tables)	3 Months Ended
	Mar. 31, 2017
Earnings Per Share [Abstract]
Schedule of Calculation of Earnings per Unit	The calculation of net income per limited partner unit is as follows: Three Months Ended March 31, 2017 2016 (millions) Net income attributable to partners $ 52.2 $ 23.1 Less: General partner allocation (1) (0.2 ) — Less: Preferred unitholder allocation 9.5 — Distributions declared on: IDRs (2) 2.9 0.4 Common unitholders 18.4 10.3 Subordinated unitholder 8.8 7.1 Total distributions declared 30.1 17.8 Undistributed earnings $ 12.8 $ 5.3 (1) See Note 2 for further information. (2) Dominion is a non-economic general partner that holds all of the IDRs. Basic and diluted net income per limited partner unit for the three months ended March 31, 2017 are as follows: Common Units Subordinated Units Series A Preferred Units General Partner (including IDRs) Total (millions, except for weighted average units and per unit data) Three Months Ended March 31, 2017 General partner allocation $ — $ — $ — $ (0.2 ) $ (0.2 ) Preferred unitholder allocation — — 9.5 — 9.5 Distributions declared 18.4 8.8 — 2.9 30.1 Undistributed earnings 8.7 4.1 — — 12.8 Net income attributable to partners (basic) $ 27.1 $ 12.9 $ 9.5 $ 2.7 $ 52.2 Dilutive effect of Series A Preferred Units (1) 9.5 — Net income attributable to partners (diluted) 36.6 12.9 Weighted average units outstanding (basic) 67,239,779 31,972,789 Dilutive effect of Series A Preferred Units (1) 30,308,342 — Weighted average units outstanding (diluted) 97,548,121 31,972,789 Net income per limited partner unit (basic) $ 0.40 $ 0.40 Net income per limited partner unit (diluted) $ 0.37 $ 0.40 (1) The dilutive effect of the Series A Preferred Units represents the reallocation of net income to limited partners including a reallocation of IDRs pursuant to the partnership agreement assuming conversion of the Series A Preferred Units into common units at the beginning of the period. Basic and diluted net income per limited partner unit for the three months ended March 31, 2016 are as follows: Common Units Subordinated Units General Partner (including IDRs) Total (millions, except for weighted average units and per unit data) Three Months Ended March 31, 2016 Distributions declared $ 10.3 $ 7.1 $ 0.4 $ 17.8 Undistributed earnings 3.1 2.2 — 5.3 Net income attributable to partners (basic and diluted) $ 13.4 $ 9.3 $ 0.4 $ 23.1 Weighted average units outstanding 45,722,112 31,972,789 Net income per limited partner unit (basic and diluted) $ 0.29 $ 0.29
Distributions Made to Limited Partner, by Distribution	The table below summarizes the quarterly distributions on common and subordinated units related to the first quarter of 2017 and 2016. Quarterly Period Ended Total Quarterly Distribution (per unit) Total Cash Distribution (in millions) Date of Declaration Date of Record Date of Distribution December 31, 2015 $ 0.2135 $ 16.8 January 21, 2016 February 5, 2016 February 15, 2016 March 31, 2016 0.2245 17.8 April 19, 2016 May 3, 2016 May 13, 2016 December 31, 2016 0.2605 27.5 January 25, 2017 February 6, 2017 February 15, 2017 March 31, 2017 0.2740 30.1 April 21, 2017 May 5, 2017 May 15, 2017
Schedule of Preferred Units	The table below summarizes the quarterly distributions on the Series A Preferred Units related to the first quarter of 2017. Quarterly Period Ended Total Distribution (in millions) Amount Payable in Cash (in millions) Amount Payable in Kind (in millions) December 31, 2016 $ 3.2 (1) $ 3.2 $ — March 31, 2017 9.5 9.5 — (1) For the period subsequent to the issuance of the Series A Preferred Units through December 31, 2016, the initial quarterly cash distribution was calculated as the minimum quarterly distribution of $0.3134 per unit prorated for the portion of the quarter subsequent to the issuance of the Series A Preferred Units.

Unit Activity (Tables)

Unit Activity (Tables)	3 Months Ended
	Mar. 31, 2017
Equity [Abstract]
Schedule of Capital Units	Activity in number of units was as follows: Convertible Preferred Common Public Dominion Public Dominion Subordinated General Partner Total (non-economic interest) Balance at December 31, 2015 — — 27,867,938 17,846,672 31,972,789 — 77,687,399 Unit-based compensation — — 7,761 — — — 7,761 Dominion purchase of common units (1) — — (377,311 ) 377,311 — — — Balance at March 31, 2016 — — 27,498,388 18,223,983 31,972,789 — 77,695,160 Balance at December 31, 2016 18,942,714 11,365,628 48,734,195 18,504,628 31,972,789 — 129,519,954 Unit-based compensation — — 10,444 — — — 10,444 Balance at March 31, 2017 18,942,714 11,365,628 48,744,639 18,504,628 31,972,789 — 129,530,398 (1) These units were purchased by Dominion as part of Dominion's program initiated in September 2015, which expired in September 2016, to purchase from the market up to $50.0 million of common units representing limited partner interests in Dominion Midstream at the discretion of Dominion's management.

Operating Revenue (Tables)

Operating Revenue (Tables)	3 Months Ended
	Mar. 31, 2017
Revenue Recognition [Abstract]
Operating Revenue	Dominion Midstream's operating revenue consists of the following: Three Months Ended March 31, 2017 2016 (millions) Gas transportation and storage $ 124.6 $ 79.1 Regulated gas sales 0.3 — Other 5.3 3.9 Total operating revenue $ 130.2 $ 83.0

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2017
Fair Value Disclosures [Abstract]
Schedule of Assets and Liabilities Measured at Fair Value on a Recurring Basis	The following table presents Dominion Midstream's assets and liabilities that are measured at fair value on a recurring basis for each hierarchy level, including both current and noncurrent portions. There were no assets or liabilities measured at fair value at December 31, 2016. Level 1 Level 2 Level 3 Total (millions) At March 31, 2017 Assets Interest rate derivative $ — $ 0.7 $ — $ 0.7 Total assets $ — $ 0.7 $ — $ 0.7 Liabilities Interest rate derivative $ — $ 1.2 $ — $ 1.2 Total liabilities $ — $ 1.2 $ — $ 1.2
Schedule Carrying Amounts and Estimated Fair Value of Financial Instruments not Recorded at Fair Value	For Dominion Midstream's financial instruments that are not recorded at fair value, the carrying amounts and estimated fair values are as follows: March 31, 2017 December 31, 2016 Carrying Estimated Fair (1) Carrying Estimated Fair (1) (millions) Long-term debt, including securities due within one year (2) $ 729.8 $ 749.8 $ 729.9 $ 744.8 (1) Fair value is estimated using market prices, where available, and interest rates currently available for issuance of debt with similar terms and remaining maturities. All fair value measurements are classified as Level 2. The carrying amount of debt issues with short-term maturities and variable rates refinanced at current market rates is a reasonable estimate of their fair value. (2) Carrying amount includes amounts which represent the unamortized debt issuance costs, discount or premium.

Derivatives and Hedge Account30

Derivatives and Hedge Accounting Activities (Tables)	3 Months Ended
	Mar. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Offsetting Assets	The tables below present Dominion Midstream's derivative asset and liability balances by type of financial instrument, before and after the effects of offsetting. There were no derivative asset or liability balances at December 31, 2016. March 31, 2017 Gross Amounts of Recognized Assets Gross Amounts Offset in the Consolidated Balance Sheet Net Amounts of Assets Presented in the Consolidated Balance Sheet (millions) Interest rate contracts: Over-the-counter $ 0.7 $ — $ 0.7 Total derivatives, subject to a master netting or similar arrangement 0.7 — 0.7 Total derivatives, not subject to a master netting or similar arrangement — — — Total $ 0.7 $ — $ 0.7 March 31, 2017 Gross Amounts Not Offset in the Consolidated Balance Sheet Net Amounts of Assets Presented in the Consolidated Balance Sheet Financial Instruments Cash Collateral Received Net Amounts (millions) Interest rate contracts: Over-the-counter $ 0.7 $ 0.7 $ — $ — Total $ 0.7 $ 0.7 $ — $ —
Offsetting Liabilities	March 31, 2017 Gross Amounts of Recognized Liabilities Gross Amounts Offset in the Consolidated Balance Sheet Net Amounts of Liabilities Presented in the Consolidated Balance Sheet (millions) Interest rate contracts: Over-the-counter $ 1.2 $ — $ 1.2 Total derivatives, subject to a master netting or similar arrangement 1.2 — 1.2 Total derivatives, not subject to a master netting or similar arrangement — — — Total $ 1.2 $ — $ 1.2 March 31, 2017 Gross Amounts Not Offset in the Consolidated Balance Sheet Net Amounts of Liabilities Presented in the Consolidated Balance Sheet Financial Instruments Cash Collateral Paid Net Amounts (millions) Interest rate contracts: Over-the-counter $ 1.2 $ 0.7 $ — $ 0.5 Total $ 1.2 $ 0.7 $ — $ 0.5
Schedule of Volume of Derivative Activity	The following table presents the volume of Dominion Midstream’s derivative activity at March 31, 2017. These volumes are based on open derivative positions and represent the combined absolute value of their long and short positions, except in the case of offsetting transactions, for which they represent the absolute value of the net volume of their long and short positions. Current Noncurrent Interest rate (1) $ — $ 300,000,000 (1) Maturity is determined based on final settlement period.
Cash Flow Hedges Included Accumulated Other Comprehensive Income (Loss)	The following table presents selected information related to gains (losses) on cash flow hedges included in AOCI in Dominion Midstream's Consolidated Balance Sheet at March 31, 2017: AOCI Amounts Expected to be Reclassified to Earnings During the Next 12 Months Maximum Term (millions) Interest rate $ (0.5 ) $ (1.2 ) 32 months Total $ (0.5 ) $ (1.2 )
Fair Value of Derivatives	The following tables present the fair values of Dominion Midstream's derivatives and where they are presented in its Consolidated Balance Sheets. Dominion Midstream did not have any derivatives at December 31, 2016. Fair Value – Total Fair Value (millions) At March 31, 2017 ASSETS Noncurrent Assets Interest rate $ 0.7 $ 0.7 Total noncurrent derivative assets (1) 0.7 0.7 Total derivative assets $ 0.7 $ 0.7 LIABILITIES Current Liabilities Interest rate $ 1.2 $ 1.2 Total current derivative liabilities (2) 1.2 1.2 Total derivative liabilities $ 1.2 $ 1.2 (1) Noncurrent derivative assets are presented in other deferred charges and other assets in Dominion Midstream's Consolidated Balance Sheets. (2) Current derivative liabilities are presented in other current liabilities in Dominion Midstream's Consolidated Balance Sheets.
Gains and Losses on Derivatives in Cash Flow Hedging Relationships	The following tables present the gains and losses on Dominion Midstream's derivatives, as well as where the associated activity is presented in its Consolidated Balance Sheets and Statements of Income. Dominion Midstream did not have any derivatives during the three months ended March 31, 2016. Derivatives in Cash Flow Hedging Relationships Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective (1) Amount of Gain (millions) Three Months Ended March 31, 2017 Derivative type and location of gains (losses): Interest rate (2) $ (0.5 ) $ — Total $ (0.5 ) $ — (1) Amounts deferred into AOCI have no associated effect in Dominion Midstream's Consolidated Statements of Income. (2) Amounts recorded in Dominion Midstream's Consolidated Statements of Income are classified in interest and related charges.

Equity Method Investments (Tabl

Equity Method Investments (Tables)	3 Months Ended
	Mar. 31, 2017
Schedule of Equity Method Investments [Line Items]
Summarized Financial Information of Equity Method Investments	The table below summarizes distributions received and income earned from Dominion Midstream's equity method investees for the three months ended March 31, 2017 and 2016. (in millions) Iroquois White River Hub Three Months Ended March 31, 2017 Distributions received $ 5.8 $ 1.2 Income from equity method investees 7.1 0.9 Three Months Ended March 31, 2016 Distributions received $ 5.8 Income from equity method investees 6.4 The table below summarizes the carrying amount of the investments and excess of investment over Dominion Midstream's share of underlying equity in net assets at March 31, 2017 and December 31, 2016. (in millions) Iroquois White River Hub March 31, 2017 December 31, 2016 March 31, 2017 December 31, 2016 Carrying amount of investment $ 219.9 $ 218.7 $ 38.9 $ 39.1 Excess of investment over Dominion Midstream's share of underlying equity in net assets (1) 122.9 122.9 16.1 16.1 (1) The difference between the carrying value of Dominion Midstream's equity method investments and its share in the underlying equity in net assets reflects equity method goodwill and is not being amortized.
Iroquois Gas Transmission System, LP
Schedule of Equity Method Investments [Line Items]
Summarized Financial Information of Equity Method Investments	Summarized financial information provided to us by Iroquois for 100% of Iroquois for the three months ended March 31, 2017 and 2016 is presented below. Three Months Ended March 31, (in millions) 2017 2016 Revenues $ 53.3 $ 53.0 Operating income 31.9 28.8 Net income 26.5 24.6
White River Hub, LLC
Schedule of Equity Method Investments [Line Items]
Summarized Financial Information of Equity Method Investments	Summarized financial information provided to us by White River Hub for 100% of White River Hub for the three months ended March 31, 2017 is presented below. Three Months Ended (in millions) March 31, 2017 Revenues $ 2.6 Operating income 1.8 Net income 1.8

Regulatory Assets and Liabili32

Regulatory Assets and Liabilities (Tables)	3 Months Ended
	Mar. 31, 2017
Regulated Operations [Abstract]
Schedule of Regulatory Assets	Regulatory assets and liabilities include the following: March 31, 2017 December 31, 2016 (millions) Regulatory assets: Unrecovered gas costs (1) $ 4.5 $ 3.3 Interest rate hedges (2) 0.6 0.6 Other 0.9 1.2 Regulatory assets-current 6.0 5.1 Income taxes recoverable through future rates (3) 4.1 3.6 Interest rate hedges (2) 33.8 34.0 Cost of reacquired debt (4) 1.4 1.5 Other 1.3 1.1 Regulatory assets-noncurrent 40.6 40.2 Total regulatory assets $ 46.6 $ 45.3 Regulatory liabilities: Overrecovered gas costs (1) $ 0.7 $ 0.4 LNG cargo obligations (5) 2.6 3.2 Customer bankruptcy settlement (6) 2.8 2.8 Other 1.9 1.1 Regulatory liabilities-current 8.0 7.5 Provision for future cost of removal and AROs (7) 101.5 100.0 Unrecognized other postretirement benefit costs (8) 12.0 11.1 Customer bankruptcy settlement (6) 16.9 17.6 Other 0.3 0.4 Regulatory liabilities-noncurrent 130.7 129.1 Total regulatory liabilities $ 138.7 $ 136.6 (1) Reflects unrecovered/overrecovered gas costs, which are subject to annual filings with FERC. (2) Reflects interest rate cash flow hedges recoverable from customers. Questar Pipeline entered into forward starting swaps totaling $150.0 million in the second and third quarters of 2011 in anticipation of issuing $180.0 million of notes in December 2011. Settlement of these swaps required payments of $37.3 million in the fourth quarter of 2011 because of declines in interest rates. These swaps qualified as cash flow hedges and the settlement payments are being amortized to interest expense over the 30 -year life of the debt. (3) Amounts to be recovered through future rates to pay income taxes that become payable by unitholders when rate revenue is provided to recover AFUDC equity when such amounts are recovered through book depreciation. (4) Represents charges incurred on the reacquisition of debt by Questar Pipeline that are deferred and amortized as interest expense over the would-be remaining life of the reacquired debt. The reacquired debt costs had a weighted-average life of approximately 3.7 years at March 31, 2017. (5) Reflects obligations to the Import Shippers for LNG cargo received. See Note 12 to the Consolidated Financial Statements in Dominion Midstream's Annual Report on Form 10-K for the year ended December 31, 2016 for further information. (6) Represents the balance of proceeds from the monetization of a bankruptcy claim acquired as part of the DCG Acquisition, which is being amortized into operating revenue through February 2024. (7) Rates charged to customers include a provision for the cost of future activities to remove assets that are expected to be incurred at the time of retirement. (8) Reflects a regulatory liability for the collection of postretirement medical costs allowed in rates in excess of expenses incurred at Questar Pipeline.
Schedule of Regulatory Liabilities	Regulatory assets and liabilities include the following: March 31, 2017 December 31, 2016 (millions) Regulatory assets: Unrecovered gas costs (1) $ 4.5 $ 3.3 Interest rate hedges (2) 0.6 0.6 Other 0.9 1.2 Regulatory assets-current 6.0 5.1 Income taxes recoverable through future rates (3) 4.1 3.6 Interest rate hedges (2) 33.8 34.0 Cost of reacquired debt (4) 1.4 1.5 Other 1.3 1.1 Regulatory assets-noncurrent 40.6 40.2 Total regulatory assets $ 46.6 $ 45.3 Regulatory liabilities: Overrecovered gas costs (1) $ 0.7 $ 0.4 LNG cargo obligations (5) 2.6 3.2 Customer bankruptcy settlement (6) 2.8 2.8 Other 1.9 1.1 Regulatory liabilities-current 8.0 7.5 Provision for future cost of removal and AROs (7) 101.5 100.0 Unrecognized other postretirement benefit costs (8) 12.0 11.1 Customer bankruptcy settlement (6) 16.9 17.6 Other 0.3 0.4 Regulatory liabilities-noncurrent 130.7 129.1 Total regulatory liabilities $ 138.7 $ 136.6 (1) Reflects unrecovered/overrecovered gas costs, which are subject to annual filings with FERC. (2) Reflects interest rate cash flow hedges recoverable from customers. Questar Pipeline entered into forward starting swaps totaling $150.0 million in the second and third quarters of 2011 in anticipation of issuing $180.0 million of notes in December 2011. Settlement of these swaps required payments of $37.3 million in the fourth quarter of 2011 because of declines in interest rates. These swaps qualified as cash flow hedges and the settlement payments are being amortized to interest expense over the 30 -year life of the debt. (3) Amounts to be recovered through future rates to pay income taxes that become payable by unitholders when rate revenue is provided to recover AFUDC equity when such amounts are recovered through book depreciation. (4) Represents charges incurred on the reacquisition of debt by Questar Pipeline that are deferred and amortized as interest expense over the would-be remaining life of the reacquired debt. The reacquired debt costs had a weighted-average life of approximately 3.7 years at March 31, 2017. (5) Reflects obligations to the Import Shippers for LNG cargo received. See Note 12 to the Consolidated Financial Statements in Dominion Midstream's Annual Report on Form 10-K for the year ended December 31, 2016 for further information. (6) Represents the balance of proceeds from the monetization of a bankruptcy claim acquired as part of the DCG Acquisition, which is being amortized into operating revenue through February 2024. (7) Rates charged to customers include a provision for the cost of future activities to remove assets that are expected to be incurred at the time of retirement. (8) Reflects a regulatory liability for the collection of postretirement medical costs allowed in rates in excess of expenses incurred at Questar Pipeline.

Related-Party Transactions (Tab

Related-Party Transactions (Tables)	3 Months Ended
	Mar. 31, 2017
Related Party Transactions [Abstract]
Schedule of Related Party Transactions	Affiliated transactions are presented below: Three Months Ended March 31, 2017 2016 (millions) Sales of natural gas transportation services to affiliates $ 22.6 $ 0.5 Services provided to affiliates 0.6 — Purchased gas from affiliates 2.5 0.1 Goods and services provided by affiliates to Dominion Midstream (1) 22.5 13.3 (1) Includes $6.9 million and $3.9 million of capitalized expenditures for the three months ended March 31, 2017 and 2016, respectively. The imbalances with affiliates are provided below: March 31, 2017 December 31, 2016 (millions) Imbalances payable to affiliates (1) $ 2.2 $ 0.1 Imbalances receivable from affiliates (2) — 6.3 (1) Recorded in other current liabilities in the Consolidated Balance Sheets. (2) Recorded in other current assets in the Consolidated Balance Sheets.

Operating Segment (Tables)

Operating Segment (Tables)	3 Months Ended
	Mar. 31, 2017
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment	The following table presents segment information pertaining to Dominion Midstream's operations: Dominion Energy Corporate and Other Total (millions) Three Months Ended March 31, 2017 Operating revenue $ 130.2 $ — $ 130.2 Earnings from equity method investees 8.0 — 8.0 Net income (loss) including noncontrolling interest and predecessors 54.5 (0.2 ) 54.3 Net income (loss) attributable to partners 52.4 (0.2 ) 52.2 Three Months Ended March 31, 2016 Operating revenue $ 83.0 $ — $ 83.0 Earnings from equity method investees 6.4 — 6.4 Net income including noncontrolling interest and predecessors 51.8 — 51.8 Net income attributable to partners 23.1 — 23.1

Description of Business and B35

Description of Business and Basis of Presentation (Details)	3 Months Ended
	Mar. 31, 2017stationmi	Dec. 31, 2015
Affiliates | Questar Pipeline | Western United States
Subsidiary, Sale of Stock [Line Items]
Length of FERC regulated interstate natural gas pipeline (in miles) (nearly 2,200 miles) | mi	2,200
Number of transmission and storage compressor stations | station	18
Iroquois Gas Transmission System, LP | Partnership Interest
Subsidiary, Sale of Stock [Line Items]
Partnership interest percentage acquired in Iroquois	25.93%	25.93%

Acquisitions (Questar Pipeline)

Acquisitions (Questar Pipeline) (Details)		Dec. 01, 2016USD ($)shares	Dec. 31, 2016USD ($)producing_area$ / sharesshares	Nov. 30, 2016USD ($)shares	Mar. 31, 2017USD ($)	Mar. 31, 2016shares	Dec. 31, 2016USD ($)producing_areami$ / sharesMMcf
Business Acquisition [Line Items]
Expected purchase of common units (in units) | shares	[1]					0
Questar Pipeline | Utah, Wyoming and Colorado
Business Acquisition [Line Items]
Length of FERC regulated interstate natural gas pipeline (in miles) (nearly 2,200 miles) | mi							2,200
Working gas storage capacity (bcf) (nearly 56 billion cubic feet) | MMcf							56,000
Number of Rocky Mountain producing areas | producing_area			6				6
Questar Pipeline | Western Colorado | White River Hub, LLC | FERC
Business Acquisition [Line Items]
Length of FERC regulated interstate natural gas pipeline (in miles) (nearly 2,200 miles) | mi							11
Ownership percentage			50.00%				50.00%
Questar Pipeline | Senior unsecured term loan | Senior unsecured term loan
Business Acquisition [Line Items]
Principal amount			$ 300,000,000				$ 300,000,000
Term of senior unsecured promissory note payable			3 years
Offering expenses associated with the term loan agreement							1,500,000
Questar Pipeline | Dominion | Subsidiary of Common Parent
Business Acquisition [Line Items]
Amount of cash consideration		$ 822,700,000
Total consideration		1,290,000,000
Amount of debt expected to remain outstanding		$ 435,000,000
Ownership percentage		100.00%
Historical cost of assets and liabilities		$ 989,300,000
Questar Pipeline | Dominion | Affiliates
Business Acquisition [Line Items]
Total transaction and transition costs incurred during the period					$ 200,000
Questar Pipeline | Dominion | Senior unsecured term loan | Senior unsecured term loan | Subsidiary of Common Parent
Business Acquisition [Line Items]
Amount of debt financed distribution		$ 300,000,000
Questar Pipeline | Dominion | Notes Payable | Senior Unsecured Promissory Note Payable | Affiliates
Business Acquisition [Line Items]
Repayment of outstanding senior unsecured promissory note payable to Dominion			$ 300,800,000
Questar Pipeline | Common Units | Dominion | Subsidiary of Common Parent
Business Acquisition [Line Items]
Number of units issued | shares		6,656,839
Value of units issued		$ 167,300,000
Number of trading days		10 days
Questar Pipeline | Common Units | Dominion | Affiliates
Business Acquisition [Line Items]
Number of trading days			10 days
Expected purchase of common units (in units) | shares			6,656,839
Amount of common units repurchased			$ 167,300,000
Questar Pipeline | Convertible Preferred Units | Series A Preferred Units | Dominion | Subsidiary of Common Parent
Business Acquisition [Line Items]
Number of units issued | shares		11,365,628
Value of units issued		$ 300,000,000
Questar Pipeline | Underwritten Public Offering
Business Acquisition [Line Items]
Proceeds from public issuance				$ 347,600,000
Questar Pipeline | Underwritten Public Offering | Common Units
Business Acquisition [Line Items]
Number of common units issued | shares				15,525,000
Estimated offering costs				$ 12,600,000
Questar Pipeline | Over-Allotment Option | Common Units
Business Acquisition [Line Items]
Number of common units issued | shares				2,025,000
Questar Pipeline | Private Placement
Business Acquisition [Line Items]
Proceeds from public issuance			$ 137,500,000
Questar Pipeline | Private Placement | Common Units
Business Acquisition [Line Items]
Number of common units issued | shares			5,990,634
Estimated offering costs							$ 3,100,000
Reduction in price of common units per Private Placement Agreement (in dollars per unit) | $ / shares			$ 0.2475				$ 0.2475
Questar Pipeline | Private Placement | Convertible Preferred Units | Series A Preferred Units
Business Acquisition [Line Items]
Number of common units issued | shares			18,942,714
Estimated offering costs							$ 9,900,000
Proceeds from issuance of convertible preferred units			$ 500,000,000
[1]	These units were purchased by Dominion as part of Dominion's program initiated in September 2015, which expired in September 2016, to purchase from the market up to $50.0 million of common units representing limited partner interests in Dominion Midstream at the discretion of Dominion's management.

Net Income Per Limited Partne37

Net Income Per Limited Partner Unit (Schedule of Earnings Per Limited Partner Unit) (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended
		Mar. 31, 2017	Dec. 31, 2016	[1]	Mar. 31, 2016
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to partners		$ 52.2			$ 23.1
Less: General partner allocation		(0.2)
Less: Preferred unitholder allocation		9.5
Total distributions declared		30.1			17.8
Undistributed earnings		12.8			$ 5.3
Common Units
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Potentially dilutive common or subordinated units outstanding (in units)					0
Less: Preferred unitholder allocation		$ 27.1			$ 13.4
Net income per limited partner unit (basic) (in dollars per unit)		$ 0.40			$ 0.29
Net income per limited partner unit (diluted) (in dollars per unit)		$ 0.37			$ 0.29
Subordinated Units
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Potentially dilutive common or subordinated units outstanding (in units)					0
Less: Preferred unitholder allocation		$ 12.9			$ 9.3
Net income per limited partner unit (basic) (in dollars per unit)		$ 0.40			$ 0.29
Net income per limited partner unit (diluted) (in dollars per unit)		$ 0.40			$ 0.29
Series A Preferred Units
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Distributions declared		$ 9.5	$ 3.2
General Partner (including IDRs)
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to partners		2.7			$ 0.4
Less: General partner allocation	[2]	(0.2)			0
IDRs	[3]	2.9			0.4
Total distributions declared		2.9			0.4
Limited Partners | Common Units
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to partners		27.1			13.4
Distributions declared	[3]	18.4			10.3
Total distributions declared		18.4			10.3
Undistributed earnings		8.7			$ 3.1
Dilutive effect of Series A Preferred Units	[4]	9.5
Net income attributable to partners (diluted)		$ 36.6
Weighted average units outstanding (basic) (in shares)		67,239,779
Dilutive effect of Series A Preferred Units (in shares)	[4]	30,308,342
Weighted average units outstanding (diluted) (in shares)		97,548,121
Net income per limited partner unit (basic) (in dollars per unit)		$ 0.40
Net income per limited partner unit (diluted) (in dollars per unit)		$ 0.37
Weighted average units outstanding (in shares)					45,722,112
Net income per limited partner unit (in dollars per unit)					$ 0.29
Limited Partners | Subordinated Units
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to partners		$ 12.9			$ 9.3
Distributions declared	[3]	8.8			7.1
Total distributions declared		8.8			7.1
Undistributed earnings		4.1			$ 2.2
Dilutive effect of Series A Preferred Units	[4]	0
Net income attributable to partners (diluted)		$ 12.9
Weighted average units outstanding (basic) (in shares)		31,972,789
Dilutive effect of Series A Preferred Units (in shares)	[4]	0
Weighted average units outstanding (diluted) (in shares)		31,972,789
Net income per limited partner unit (basic) (in dollars per unit)		$ 0.40
Net income per limited partner unit (diluted) (in dollars per unit)		$ 0.40
Weighted average units outstanding (in shares)					31,972,789
Net income per limited partner unit (in dollars per unit)					$ 0.29
Limited Partners | Series A Preferred Units
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to partners		$ 9.5
Less: Preferred unitholder allocation		$ 9.5			$ 0
[1]	For the period subsequent to the issuance of the Series A Preferred Units through December 31, 2016, the initial quarterly cash distribution was calculated as the minimum quarterly distribution of $0.3134 per unit prorated for the portion of the quarter subsequent to the issuance of the Series A Preferred Units.
[2]	See Note 2 for further information.
[3]	Dominion is a non-economic general partner that holds all of the IDRs.
[4]	The dilutive effect of the Series A Preferred Units represents the reallocation of net income to limited partners including a reallocation of IDRs pursuant to the partnership agreement assuming conversion of the Series A Preferred Units into common units at the beginning of the period.

(Schedule of Quarterly Distribu

(Schedule of Quarterly Distributions on Common and Subordinated Units) (Details) - USD ($) $ / shares in Units, $ in Millions	May 15, 2017	Feb. 15, 2017	May 13, 2016	Feb. 15, 2016
Distribution Made to Limited Partner [Line Items]
Total Quarterly Distribution (per unit)		$ 0.2605	$ 0.2245	$ 0.2135
Total Cash Distribution (in millions)		$ 27.5	$ 17.8	$ 16.8
Subsequent Event | Scenario, Forecast
Distribution Made to Limited Partner [Line Items]
Total Quarterly Distribution (per unit)	$ 0.2740
Total Cash Distribution (in millions)	$ 30.1

Net Income Per Limited Partne39

Net Income Per Limited Partner Unit (Schedule of Quarterly Distributions on Series A Preferred Units) (Details) - Series A Preferred Units - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended
	Dec. 31, 2016	Mar. 31, 2017	Dec. 31, 2016
Distribution Made to Limited Partner [Line Items]
Quarterly distributions (in dollars per unit)		$ 0.3134
Total Distribution (in millions)		$ 9.5	$ 3.2	[1]
Amount Payable in Cash (in millions)	$ 3.2	9.5	3.2
Amount Payable in Kind (in millions)		$ 0	$ 0
Minimum
Distribution Made to Limited Partner [Line Items]
Distributions declared per limited partner unit (in dollars per unit)	$ 0.3134
[1]	For the period subsequent to the issuance of the Series A Preferred Units through December 31, 2016, the initial quarterly cash distribution was calculated as the minimum quarterly distribution of $0.3134 per unit prorated for the portion of the quarter subsequent to the issuance of the Series A Preferred Units.

Unit Activity (Details)

Unit Activity (Details) - USD ($)		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016	Sep. 30, 2015
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance (in units)		129,519,954	77,687,399
Unit-based compensation (in units)		10,444	7,761
Dominion purchase of common units (in units)	[1]		0
Balance (in units)		129,530,398	77,695,160
Dominion
Increase (Decrease) in Partners' Capital [Roll Forward]
Amount of common units authorized to be purchased				$ 50,000,000
General Partner Dominion (non-economic interest) | General Partner Dominion (non-economic interest) | Dominion
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance (in units)		0	0
Unit-based compensation (in units)		0	0
Dominion purchase of common units (in units)	[1]		0
Balance (in units)		0	0
Preferred Unitholders Public | Preferred Stock | Limited Partners
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance (in units)		18,942,714	0
Unit-based compensation (in units)		0	0
Dominion purchase of common units (in units)	[1]		0
Balance (in units)		18,942,714	0
Preferred Unitholder Dominion | Preferred Stock | Limited Partners | Dominion
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance (in units)		11,365,628	0
Unit-based compensation (in units)		0	0
Dominion purchase of common units (in units)	[1]		0
Balance (in units)		11,365,628	0
Common Units | Common Unitholders and Subordinated Unitholder | Limited Partners
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance (in units)		48,734,195	27,867,938
Unit-based compensation (in units)		10,444	7,761
Dominion purchase of common units (in units)	[1]		(377,311)
Balance (in units)		48,744,639	27,498,388
Common Units | Common Unitholders and Subordinated Unitholder | Limited Partners | Dominion
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance (in units)		18,504,628	17,846,672
Unit-based compensation (in units)		0	0
Dominion purchase of common units (in units)	[1]		377,311
Balance (in units)		18,504,628	18,223,983
Subordinated Units | Common Unitholders and Subordinated Unitholder | Limited Partners | Dominion
Increase (Decrease) in Partners' Capital [Roll Forward]
Balance (in units)		31,972,789	31,972,789
Unit-based compensation (in units)		0	0
Dominion purchase of common units (in units)	[1]		0
Balance (in units)		31,972,789	31,972,789
[1]	These units were purchased by Dominion as part of Dominion's program initiated in September 2015, which expired in September 2016, to purchase from the market up to $50.0 million of common units representing limited partner interests in Dominion Midstream at the discretion of Dominion's management.

Operating Revenue (Details)

Operating Revenue (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Revenue Recognition [Abstract]
Gas transportation and storage		$ 124.6	$ 79.1
Regulated gas sales		0.3	0
Other		5.3	3.9
Total operating revenue	[1]	$ 130.2	$ 83
[1]	See Note 15 for amounts attributable to related parties.

Fair Value Measurements (Schedu

Fair Value Measurements (Schedule of Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) $ in Millions	Mar. 31, 2017USD ($)
Assets
Interest rate derivative	$ 0.7
Liabilities
Interest rate derivative	1.2
Fair Value, Measurements, Recurring
Assets
Total assets	0.7
Liabilities
Total liabilities	1.2
Fair Value, Measurements, Recurring | Level 1
Assets
Total assets	0
Liabilities
Total liabilities	0
Fair Value, Measurements, Recurring | Level 2
Assets
Total assets	0.7
Liabilities
Total liabilities	1.2
Fair Value, Measurements, Recurring | Level 3
Assets
Total assets	0
Liabilities
Total liabilities	0
Fair Value, Measurements, Recurring | Interest rate derivative
Assets
Interest rate derivative	0.7
Liabilities
Interest rate derivative	1.2
Fair Value, Measurements, Recurring | Interest rate derivative | Level 1
Assets
Interest rate derivative	0
Liabilities
Interest rate derivative	0
Fair Value, Measurements, Recurring | Interest rate derivative | Level 2
Assets
Interest rate derivative	0.7
Liabilities
Interest rate derivative	1.2
Fair Value, Measurements, Recurring | Interest rate derivative | Level 3
Assets
Interest rate derivative	0
Liabilities
Interest rate derivative	$ 0

Fair Value Measurements (Sche43

Fair Value Measurements (Schedule of Carrying Amounts and Estimated Fair Values of Financial Instruments not Recorded at Fair Value) (Details) - USD ($) $ in Millions		Mar. 31, 2017	Dec. 31, 2016
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, including securities due within one year	[1]	$ 729.8	$ 729.9
Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, including securities due within one year	[1],[2]	$ 749.8	$ 744.8
[1]	Carrying amount includes amounts which represent the unamortized debt issuance costs, discount or premium.
[2]	Fair value is estimated using market prices, where available, and interest rates currently available for issuance of debt with similar terms and remaining maturities. All fair value measurements are classified as Level 2. The carrying amount of debt issues with short-term maturities and variable rates refinanced at current market rates is a reasonable estimate of their fair value.

Derivatives and Hedge Account44

Derivatives and Hedge Accounting Activities (Schedule of Offsetting Assets) (Details) $ in Millions	Mar. 31, 2017USD ($)
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	$ 0.7
Gross Amounts Offset in the Consolidated Balance Sheet	0
Net Amounts of Assets Presented in the Consolidated Balance Sheet	0.7
Total derivatives, not subject to a master netting or similar arrangement	0
Gross Amounts of Recognized Assets, Total	0.7
Derivative Asset	0.7
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	0.7
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received	0
Net Amounts	0
Interest rate derivative | Over-the-counter
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	0.7
Gross Amounts Offset in the Consolidated Balance Sheet	0
Net Amounts of Assets Presented in the Consolidated Balance Sheet	0.7
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	0.7
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral Received	0
Net Amounts	$ 0

Derivatives and Hedge Account45

Derivatives and Hedge Accounting Activities (Schedule of Offsetting Liabilities) (Details) $ in Millions	Mar. 31, 2017USD ($)
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	$ 1.2
Gross Amounts Offset in the Consolidated Balance Sheet	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	1.2
Total derivatives, not subject to a master netting or similar arrangement	0
Gross Amounts of Recognized Liabilities, Total	1.2
Derivative Liabilities	1.2
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	0.7
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral	0
Net Amounts	0.5
Interest rate derivative | Over-the-counter
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	1.2
Gross Amounts Offset in the Consolidated Balance Sheet	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	1.2
Gross Amounts Not Offset in the Consolidated Balance Sheet, Financial Instruments	0.7
Gross Amounts Not Offset in the Consolidated Balance Sheet, Cash Collateral	0
Net Amounts	$ 0.5

Derivatives and Hedge Account46

Derivatives and Hedge Accounting Activities (Volume of Derivative Activity) (Details) $ in Millions	Mar. 31, 2017USD ($)	[1]
Interest Rate - Current Derivative Contract
Derivative [Line Items]
Interest rate	$ 0
Interest Rate - Non-current Derivative Contract
Derivative [Line Items]
Interest rate	$ 300
[1]	Maturity is determined based on final settlement period.

Derivatives and Hedge Account47

Derivatives and Hedge Accounting Activities (Selected Information Related to Gains (Losses) on Cash Flow Hedges Included in AOCI) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2017USD ($)
Derivative Instruments, Gain (Loss) [Line Items]
AOCI	$ (0.5)
Amounts Expected to be Reclassified to Earnings During the Next 12 Months	(1.2)
Interest rate derivative
Derivative Instruments, Gain (Loss) [Line Items]
AOCI	(0.5)
Amounts Expected to be Reclassified to Earnings During the Next 12 Months	$ (1.2)
Maximum Term	32 months

Derivatives and Hedge Account48

Derivatives and Hedge Accounting Activities (Fair Value of Derivatives) (Details) $ in Millions	Mar. 31, 2017USD ($)
Derivatives, Fair Value [Line Items]
Interest rate derivative	$ 0.7
Interest rate derivative	1.2
Noncurrent Assets
Derivatives, Fair Value [Line Items]
Interest rate derivative	0.7	[1]
Noncurrent Assets | Interest rate derivative
Derivatives, Fair Value [Line Items]
Interest rate derivative	0.7
Current Liabilities
Derivatives, Fair Value [Line Items]
Interest rate derivative	1.2	[2]
Current Liabilities | Interest rate derivative
Derivatives, Fair Value [Line Items]
Interest rate derivative	1.2
Fair Value – Derivatives under Hedge Accounting
Derivatives, Fair Value [Line Items]
Interest rate derivative	0.7
Interest rate derivative	1.2
Fair Value – Derivatives under Hedge Accounting | Noncurrent Assets
Derivatives, Fair Value [Line Items]
Interest rate derivative	0.7	[1]
Fair Value – Derivatives under Hedge Accounting | Noncurrent Assets | Interest rate derivative
Derivatives, Fair Value [Line Items]
Interest rate derivative	0.7
Fair Value – Derivatives under Hedge Accounting | Current Liabilities
Derivatives, Fair Value [Line Items]
Interest rate derivative	1.2	[2]
Fair Value – Derivatives under Hedge Accounting | Current Liabilities | Interest rate derivative
Derivatives, Fair Value [Line Items]
Interest rate derivative	$ 1.2
[1]	Noncurrent derivative assets are presented in other deferred charges and other assets in Dominion Midstream's Consolidated Balance Sheets.
[2]	Current derivative liabilities are presented in other current liabilities in Dominion Midstream's Consolidated Balance Sheets.

Derivatives and Hedge Account49

Derivatives and Hedge Accounting Activities (Gains and Losses on Derivatives in Cash Flow Hedging Relationships) (Details) - Cash Flow Hedges $ in Millions	3 Months Ended
	Mar. 31, 2017USD ($)
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion)	$ (0.5)	[1]
Amount of Gain (Loss) Reclassified From AOCI to Income	0
Interest rate derivative
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion)	(0.5)	[1],[2]
Amount of Gain (Loss) Reclassified From AOCI to Income	$ 0	[2]
[1]	Amounts deferred into AOCI have no associated effect in Dominion Midstream's Consolidated Statements of Income.
[2]	Amounts recorded in Dominion Midstream's Consolidated Statements of Income are classified in interest and related charges.

Equity Method Investments (Deta

Equity Method Investments (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016		Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Income from equity method investees		$ 8	$ 6.4
Carrying amount of investment		258.8		$ 257.8	[1]
Iroquois Gas Transmission System, LP
Schedule of Equity Method Investments [Line Items]
Distributions received		5.8	5.8
Income from equity method investees		7.1	6.4
Carrying amount of investment		219.9		218.7
Excess of investment over Dominion Midstream's share of underlying equity in net assets	[2]	$ 122.9		122.9
Iroquois Gas Transmission System, LP | Partnership Interest
Schedule of Equity Method Investments [Line Items]
Partnership interest percentage acquired in Iroquois		25.93%				25.93%
Percentage of financial information provided		100.00%
Equity Method Investment, Summarized Financial Information [Abstract]
Revenues		$ 53.3	53
Operating income		31.9	28.8
Net income		26.5	$ 24.6
White River Hub, LLC
Schedule of Equity Method Investments [Line Items]
Distributions received		1.2
Income from equity method investees		0.9
Carrying amount of investment		38.9		39.1
Excess of investment over Dominion Midstream's share of underlying equity in net assets	[2]	$ 16.1		$ 16.1
White River Hub, LLC | Partnership Interest
Schedule of Equity Method Investments [Line Items]
Partnership interest percentage acquired in Iroquois		50.00%
Percentage of financial information provided		100.00%
Equity Method Investment, Summarized Financial Information [Abstract]
Revenues		$ 2.6
Operating income		1.8
Net income		$ 1.8
[1]	Dominion Midstream's Consolidated Balance Sheet at December 31, 2016 has been derived from the audited Consolidated Balance Sheet at that date.
[2]	The difference between the carrying value of Dominion Midstream's equity method investments and its share in the underlying equity in net assets reflects equity method goodwill and is not being amortized.

Regulatory Assets and Liabili51

Regulatory Assets and Liabilities (Regulatory Assets) (Details) - USD ($)		1 Months Ended	3 Months Ended
		Dec. 31, 2011	Mar. 31, 2017	Dec. 31, 2011	Dec. 31, 2016		Sep. 30, 2011
Regulatory Assets [Line Items]
Regulatory assets-current			$ 6,000,000		$ 5,100,000	[1]
Regulatory assets-noncurrent			40,600,000		40,200,000	[1]
Total regulatory assets			46,600,000		45,300,000
Past expenditures in which no return is expected			$ 40,700,000
Recovery period of expenditures			2 years
Questar Pipeline | Notes Payable
Regulatory Assets [Line Items]
Principal amount		$ 180,000,000		$ 180,000,000
Settlement of swaps				$ 37,300,000
Life of debt		30 years
Questar Pipeline | Fair Value – Derivatives under Hedge Accounting | Notes Payable | Interest Rate Swap
Regulatory Assets [Line Items]
Total forward starting interest rate swaps							$ 150,000,000
Unrecovered gas costs
Regulatory Assets [Line Items]
Regulatory assets-current	[2]		$ 4,500,000		3,300,000
Interest rate hedges
Regulatory Assets [Line Items]
Regulatory assets-current	[3]		600,000		600,000
Regulatory assets-noncurrent	[3]		33,800,000		34,000,000
Other
Regulatory Assets [Line Items]
Regulatory assets-current			900,000		1,200,000
Regulatory assets-noncurrent			1,300,000		1,100,000
Income taxes recoverable through future rates
Regulatory Assets [Line Items]
Regulatory assets-noncurrent	[4]		4,100,000		3,600,000
Cost of reacquired debt
Regulatory Assets [Line Items]
Regulatory assets-noncurrent	[5]		$ 1,400,000		$ 1,500,000
Cost of reacquired debt | Weighted Average
Regulatory Assets [Line Items]
Weighted average life of reacquired debt			3 years 8 months 24 days
[1]	Dominion Midstream's Consolidated Balance Sheet at December 31, 2016 has been derived from the audited Consolidated Balance Sheet at that date.
[2]	Reflects unrecovered/overrecovered gas costs, which are subject to annual filings with FERC.
[3]	Reflects interest rate cash flow hedges recoverable from customers. Questar Pipeline entered into forward starting swaps totaling $150.0 million in the second and third quarters of 2011 in anticipation of issuing $180.0 million of notes in December 2011. Settlement of these swaps required payments of $37.3 million in the fourth quarter of 2011 because of declines in interest rates. These swaps qualified as cash flow hedges and the settlement payments are being amortized to interest expense over the 30-year life of the debt.
[4]	Amounts to be recovered through future rates to pay income taxes that become payable by unitholders when rate revenue is provided to recover AFUDC equity when such amounts are recovered through book depreciation.
[5]	Represents charges incurred on the reacquisition of debt by Questar Pipeline that are deferred and amortized as interest expense over the would-be remaining life of the reacquired debt. The reacquired debt costs had a weighted-average life of approximately 3.7 years at March 31, 2017.

Regulatory Assets and Liabili52

Regulatory Assets and Liabilities (Regulatory Liabilities) (Details) - USD ($) $ in Millions		Mar. 31, 2017	Dec. 31, 2016
Regulatory Liabilities [Line Items]
Regulatory liabilities-current		$ 8	$ 7.5	[1]
Regulatory liabilities-noncurrent		130.7	129.1	[1]
Total regulatory liabilities		138.7	136.6
Overrecovered gas costs
Regulatory Liabilities [Line Items]
Regulatory liabilities-current	[2]	0.7	0.4
LNG cargo obligations
Regulatory Liabilities [Line Items]
Regulatory liabilities-current	[3]	2.6	3.2
Customer bankruptcy settlement
Regulatory Liabilities [Line Items]
Regulatory liabilities-current	[4]	2.8	2.8
Regulatory liabilities-noncurrent	[4]	16.9	17.6
Other
Regulatory Liabilities [Line Items]
Regulatory liabilities-current		1.9	1.1
Regulatory liabilities-noncurrent		0.3	0.4
Provision for future cost of removal
Regulatory Liabilities [Line Items]
Regulatory liabilities-noncurrent	[5]	101.5	100
Unrecognized other postretirement benefit costs
Regulatory Liabilities [Line Items]
Regulatory liabilities-noncurrent	[6]	$ 12	$ 11.1
[1]	Dominion Midstream's Consolidated Balance Sheet at December 31, 2016 has been derived from the audited Consolidated Balance Sheet at that date.
[2]	Reflects unrecovered/overrecovered gas costs, which are subject to annual filings with FERC.
[3]	Reflects obligations to the Import Shippers for LNG cargo received. See Note 12 to the Consolidated Financial Statements in Dominion Midstream's Annual Report on Form 10-K for the year ended December 31, 2016 for further information.
[4]	Represents the balance of proceeds from the monetization of a bankruptcy claim acquired as part of the DCG Acquisition, which is being amortized into operating revenue through February 2024.
[5]	Rates charged to customers include a provision for the cost of future activities to remove assets that are expected to be incurred at the time of retirement.
[6]	Reflects a regulatory liability for the collection of postretirement medical costs allowed in rates in excess of expenses incurred at Questar Pipeline.

Variable Interest Entities (Det

Variable Interest Entities (Details) - Services provided by Affiliates - Variable Interest Entity, Not Primary Beneficiary - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
General Partner (including IDRs) | DRS
Variable Interest Entity [Line Items]
Reimbursable costs	$ 400,000	$ 300,000
Affiliates
Variable Interest Entity [Line Items]
Amounts due from affiliates	4,400,000		$ 6,300,000
Amounts due to Dominion Midstream	400,000		$ 0
Affiliates | DRS
Variable Interest Entity [Line Items]
Services purchased	6,900,000	6,700,000
Affiliates | DCGS
Variable Interest Entity [Line Items]
Services purchased	3,200,000	$ 5,000,000
Affiliates | QPC Services Company
Variable Interest Entity [Line Items]
Services purchased	$ 6,900,000

Commitments and Contingencies (

Commitments and Contingencies (Details)	Mar. 31, 2017USD ($)
Surety Bond
Other Commitments [Line Items]
Total amount of commitment	$ 13,100,000
Surety Bond | Cove Point
Other Commitments [Line Items]
Total amount of commitment	9,800,000
Annual Contributions to Cove Point Natural Heritage Trust
Other Commitments [Line Items]
Total amount of commitment	300,000
Annual Contributions to Cove Point Natural Heritage Trust | Minimum
Other Commitments [Line Items]
Total amount of commitment	$ 0

Credit Risk (Details)

Credit Risk (Details) $ in Millions	3 Months Ended
	Mar. 31, 2017USD ($)customer	Mar. 31, 2016	Dec. 31, 2016USD ($)
Customer Concentration Risk | Sales Revenue, Net
Concentration Risk [Line Items]
Number of customers | customer	130
Customer Concentration Risk | Sales Revenue, Net | Three Largest Customers
Concentration Risk [Line Items]
Percentage of total transportation and storage revenues	42.00%	42.00%
Customer Concentration Risk | Sales Revenue, Net | Two Largest Customers
Concentration Risk [Line Items]
Percentage of total transportation and storage revenues		72.00%
Customer Concentration Risk | Sales Revenue, Net | Largest Customer
Concentration Risk [Line Items]
Percentage of total transportation and storage revenues	16.00%	56.00%
Credit Concentration Risk | Accounts Receivable
Concentration Risk [Line Items]
Provision for credit losses (less than $0.1 million) | $	$ 0.1		$ 0.1

Related-Party Transactions (Det

Related-Party Transactions (Details) - Affiliates - USD ($)		1 Months Ended		3 Months Ended
		Apr. 30, 2017	Dec. 31, 2016	Mar. 31, 2017	Mar. 31, 2016	Oct. 20, 2014
Related Party Transaction [Line Items]
Capital expenditures				$ 6,900,000	$ 3,900,000
Imbalances payable to affiliates	[1]		$ 100,000	2,200,000
Imbalances receivable from affiliates	[2]		6,300,000	0
Reimbursement of Transition Services Costs by Affiliate | DCG
Related Party Transaction [Line Items]
Goods and services provided by affiliates				0	600,000
Sales of Natural Gas Transportation Services to Affiliates
Related Party Transaction [Line Items]
Sales of natural gas transportation services to affiliates				22,600,000	500,000
Services Provided to Affiliates
Related Party Transaction [Line Items]
Sales of natural gas transportation services to affiliates				600,000	0
Purchased Gas from Affiliates
Related Party Transaction [Line Items]
Purchased gas from affiliates				2,500,000	100,000
Goods and Services Provided by Affiliates
Related Party Transaction [Line Items]
Goods and services provided by affiliates	[3]			22,500,000	13,300,000
Credit Facility with Dominion | Subsequent Event
Related Party Transaction [Line Items]
Amount drawn on Dominion credit facility		$ 6,900,000
Credit Facility with Dominion | Line of Credit
Related Party Transaction [Line Items]
Amount outstanding against the credit facility			63,200,000	$ 67,900,000
Termination notice period				90 days
Interest charges related to borrowing from Dominion (less than $0.1 million for the three months ended March 31, 2016)				$ 400,000	100,000
Credit Facility with Dominion | IPO | Line of Credit
Related Party Transaction [Line Items]
Borrowing capacity						$ 300,000,000
Capital Expenditures related to Liquefaction Project | Cove Point
Related Party Transaction [Line Items]
Amount of contribution				329,200,000	244,900,000
Capital Expenditures related to Liquefaction Project | Cove Point | Subsequent Event
Related Party Transaction [Line Items]
Amount of contribution		$ 45,700,000
Dominion
Related Party Transaction [Line Items]
Amounts due to Dominion associated with benefit plans			6,200,000	6,700,000
Amounts due from Dominion			$ 900,000	1,300,000
Dominion | Questar Pipeline
Related Party Transaction [Line Items]
Total transaction and transition costs incurred during the period				200,000
Dominion | Questar Pipeline | Partnership Interest
Related Party Transaction [Line Items]
Total transaction and transition costs incurred during the period				$ 200,000
Dominion | Senior Unsecured Promissory Note Payable | Notes Payable
Related Party Transaction [Line Items]
Interest charges related to borrowing from Dominion (less than $0.1 million for the three months ended March 31, 2016)					$ 500,000
Dominion | Senior Unsecured Promissory Note Payable | Notes Payable | DCG
Related Party Transaction [Line Items]
Term of senior unsecured promissory note payable			2 years
Repayment of outstanding senior unsecured promissory note payable to Dominion			$ 300,800,000
Dominion | Senior Unsecured Promissory Note Payable | Notes Payable | Questar Pipeline
Related Party Transaction [Line Items]
Repayment of outstanding senior unsecured promissory note payable to Dominion			$ 300,800,000
[1]	Recorded in other current liabilities in the Consolidated Balance Sheets.
[2]	Recorded in other current assets in the Consolidated Balance Sheets.
[3]	Includes $6.9 million and $3.9 million of capitalized expenditures for the three months ended March 31, 2017 and 2016, respectively.

Operating Segment (Details)

Operating Segment (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Segment Reporting Information [Line Items]
Operating revenue	[1]	$ 130.2	$ 83
Earnings from equity method investees		8	6.4
Net income (loss) including noncontrolling interest and predecessors		54.3	51.8
Net income (loss) attributable to partners		52.2	23.1
Operating Segments | Dominion Energy
Segment Reporting Information [Line Items]
Operating revenue		130.2	83
Earnings from equity method investees		8	6.4
Net income (loss) including noncontrolling interest and predecessors		54.5	51.8
Net income (loss) attributable to partners		52.4	23.1
Operating Segments | Corporate and Other
Segment Reporting Information [Line Items]
Operating revenue		0	0
Earnings from equity method investees		0	0
Net income (loss) including noncontrolling interest and predecessors		(0.2)	0
Net income (loss) attributable to partners		$ (0.2)	$ 0
[1]	See Note 15 for amounts attributable to related parties.