Dominion Energy Midstream Partners 10-K 27 Feb 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2014	Jun. 30, 2014	Jan. 31, 2015
Document and Entity Information [Line Items]
Document Type	10-K
Amendment Flag	FALSE
Document Period End Date	31-Dec-14
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY
Trading Symbol	DM
Entity Registrant Name	Dominion Midstream Partners, LP
Entity Central Index Key	1603286
Current Fiscal Year End Date	-19
Entity Filer Category	Non-accelerated Filer
Entity Well Known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Public Float		$0
Entity Common Units Outstanding
Document and Entity Information [Line Items]
Entity Units Outstanding			31,980,166
Entity Subordinated Units Outstanding
Document and Entity Information [Line Items]
Entity Units Outstanding			31,972,789

Consolidated_Statements_of_Inc

Consolidated Statements of Income (USD $)	3 Months Ended		12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Operating Revenue			$313.30	[1]
Operating Expenses
Purchased gas			59.6	[1]
Other operations and maintenance:
Affiliated suppliers			9.4
Other			25.5
Depreciation and amortization			37.7
Other taxes			22.4
Total operating expenses			154.6
Income from operations			158.7
Interest and related charges			0	[1]
Income from operations including noncontrolling interest before income taxes			158.7
Income tax expense			51.8	[2]
Net Income including noncontrolling interest	26.3	[3]	106.9
Less: Net income attributable to noncontrolling interest subsequent to initial public offering	16.8
Net income attributable to partners' ownership interest subsequent to initial public offering
Net income attributable to limited partners subsequent to initial public offering	9.5
Net income subsequent to initial public offering per unit (basic and diluted)
Net income subsequent to initial public offering per unit (basic and diluted)	$0.15
Common Units
Net income attributable to partners' ownership interest subsequent to initial public offering
Net income attributable to limited partners subsequent to initial public offering	4.8	[3]
Net income subsequent to initial public offering per unit (basic and diluted)
Net income subsequent to initial public offering per unit (basic and diluted)	$0.15
Subordinated Units
Net income attributable to partners' ownership interest subsequent to initial public offering
Net income attributable to limited partners subsequent to initial public offering	4.7	[3]
Net income subsequent to initial public offering per unit (basic and diluted)
Net income subsequent to initial public offering per unit (basic and diluted)	$0.15
Predecessor
Operating Revenue					343.5	[1]	293	[1]
Operating Expenses
Purchased gas					91.7	[1]	48.8	[1]
Other operations and maintenance:
Affiliated suppliers					7.7		7
Other					20.2		20.2
Depreciation and amortization					31.7		33.3
Other taxes					21.1		20.5
Total operating expenses					172.4		129.8
Income from operations					171.1		163.2
Interest and related charges					0	[1]	0.1	[1]
Income from operations including noncontrolling interest before income taxes					171.1		163.1
Income tax expense					61.7		65.9
Net Income including noncontrolling interest			$106.90		$109.40		$97.20
[1]	See Note 14 for amounts attributable to related parties.
[2]	Income taxes recognized prior to the Offering.
[3]	Allocation of net income attributable to partners' ownership interest subsequent to initial public offering has been adjusted for rounding.

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 31, 2014		Dec. 31, 2013
In Millions, unless otherwise specified
Current Assets
Cash and cash equivalents	$175.40		$11.20
Customer receivables	19.9
Affiliated receivables	6.1
Prepayments	9.5
Materials and supplies	8.7
Regulatory assets	1.7
Other	4.7
Total current assets	226
Property, Plant and Equipment
Property, plant and equipment	2,203.10
Accumulated depreciation and amortization	-231.2
Total property, plant and equipment, net	1,971.90
Deferred Charges and Other Assets
Goodwill	45.9	[1]
Intangible assets, net	12.1
Regulatory assets	2.5
Total deferred charges and other assets	60.5
Total assets	2,258.40
Current Liabilities
Accounts payable	3.3
Payables to affiliates	2.5
Accrued payroll and taxes	1.5	[2]
Regulatory liabilities	3.6
Deferred revenue	3.9
Natural gas imbalances	2.7	[2]
CPCN obligation	7.9
Other	6.4
Total current liabilities	31.8
Deferred Credits and Other Liabilities
Deferred income taxes	0
Pension and other postretirement benefit liabilities	4.4	[2]
Regulatory liabilities	33.5
CPCN obligation	36.2
Other	1.7	[2]
Total deferred credits and other liabilities	75.8
Total liabilities	107.6
Commitments and Contingencies (see Note 12)
Equity and Partners' Capital
Predecessor member's equity	0
Total Dominion Midstream Partners, LP partners' equity and capital	1,075.30
Noncontrolling interest	1,075.50
Total equity and partners' capital	2,150.80
Total liabilities and equity and partners' capital	2,258.40
Common Units
Equity and Partners' Capital
Common unitholders and Subordinated unitholder	395.4
Dominion
Equity and Partners' Capital
General Partner interest - Dominion (non-economic interest)	0
Dominion | Common Units
Equity and Partners' Capital
Common unitholders and Subordinated unitholder	213.7
Dominion | Subordinated Units
Equity and Partners' Capital
Common unitholders and Subordinated unitholder	466.2
Predecessor
Current Assets
Cash and cash equivalents			11.2
Customer receivables			20
Affiliated receivables			4.7
Prepayments			8.7
Materials and supplies			8.4
Regulatory assets			5.5
Other			11.4
Total current assets			69.9
Property, Plant and Equipment
Property, plant and equipment			1,565.70
Accumulated depreciation and amortization			-198.3
Total property, plant and equipment, net			1,367.40
Deferred Charges and Other Assets
Goodwill			45.9	[1]
Intangible assets, net			12.5
Regulatory assets			2.5
Total deferred charges and other assets			60.9
Total assets			1,498.20
Current Liabilities
Accounts payable			3
Payables to affiliates			20.4
Accrued payroll and taxes			2.2	[2]
Regulatory liabilities			7.7
Deferred revenue			3.6
Natural gas imbalances			9.4	[2]
CPCN obligation			0
Other			8.6
Total current liabilities			54.9
Deferred Credits and Other Liabilities
Deferred income taxes			135.1
Pension and other postretirement benefit liabilities			4.1	[2]
Regulatory liabilities			30.4
CPCN obligation			0
Other			1.7	[2]
Total deferred credits and other liabilities			171.3
Total liabilities			226.2
Commitments and Contingencies (see Note 12)
Equity and Partners' Capital
Predecessor member's equity			1,272
Total Dominion Midstream Partners, LP partners' equity and capital			1,272
Noncontrolling interest			0
Total equity and partners' capital			1,272
Total liabilities and equity and partners' capital			1,498.20
Predecessor | Common Units
Equity and Partners' Capital
Common unitholders and Subordinated unitholder			0
Predecessor | Dominion
Equity and Partners' Capital
General Partner interest - Dominion (non-economic interest)			0
Predecessor | Dominion | Common Units
Equity and Partners' Capital
Common unitholders and Subordinated unitholder			0
Predecessor | Dominion | Subordinated Units
Equity and Partners' Capital
Common unitholders and Subordinated unitholder			$0
[1]	There are no accumulated impairment losses.
[2]	See Note 14 for amounts attributable to related parties.

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical)	Dec. 31, 2014
Common Units
Common unitholders and Subordinated unitholders- units issued	20,127,322
Common unitholders and Subordinated unitholders- units outstanding	20,127,322
Dominion | Common Units
Common unitholders and Subordinated unitholders- units issued	11,847,789
Common unitholders and Subordinated unitholders- units outstanding	11,847,789
Dominion | Subordinated Units
Common unitholders and Subordinated unitholders- units issued	31,972,789
Common unitholders and Subordinated unitholders- units outstanding	31,972,789

Consolidated_Statements_of_Cha

Consolidated Statements of Changes in Equity and Partners' Capital (USD $)		Total	IPO	Predecessor	Predecessor Members' Equity	Predecessor Members' Equity	Predecessor Members' Equity	Common Unitholders and Subordinated Unitholder	Common Unitholders and Subordinated Unitholder	Common Unitholders and Subordinated Unitholder	Common Unitholders and Subordinated Unitholder	Common Unitholders and Subordinated Unitholder	Common Unitholders and Subordinated Unitholder	Common Unitholders and Subordinated Unitholder	Common Unitholders and Subordinated Unitholder	Common Unitholders and Subordinated Unitholder	General Partner Dominion (non-economic interest)	General Partner Dominion (non-economic interest)	General Partner Dominion (non-economic interest)	Total Dominion Midstream Partners, LP Partners' Equity and Capital	Total Dominion Midstream Partners, LP Partners' Equity and Capital	Total Dominion Midstream Partners, LP Partners' Equity and Capital	Noncontrolling interest	Noncontrolling interest	Noncontrolling interest
In Millions, unless otherwise specified						IPO	Predecessor	Common Units	Common Units	Common Units	Common Units	Subordinated Units	Subordinated Units	Predecessor	Predecessor	Predecessor	Dominion	Dominion	Predecessor		IPO	Predecessor		IPO	Predecessor
									IPO	Dominion	Dominion	Dominion	Dominion	Common Units	Common Units	Subordinated Units		IPO	Dominion
											IPO		IPO		Dominion	Dominion
Balance at Dec. 31, 2011				$659.60			$659.60							$0	$0	$0			$0			$659.60			$0
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income				97.2			97.2							0	0	0			0			97.2			0
Contributions from Dominion				3.4			3.4							0	0	0			0			3.4			0
Formation and Offering Transactions:
Distributions				-61.7			-61.7							0	0	0			0			-61.7			0
Balance at Dec. 31, 2012				698.5			698.5							0	0	0			0			698.5			0
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income				24.5
Balance at Mar. 31, 2013
Balance at Dec. 31, 2012				698.5			698.5							0	0	0			0			698.5			0
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income				109.4			109.4							0	0	0			0			109.4			0
Contributions from Dominion				464.1			464.1							0	0	0			0			464.1			0
Balance at Dec. 31, 2013				1,272			1,272							0	0	0			0			1,272			0
Balance at Sep. 30, 2013
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income				27.3
Balance at Dec. 31, 2013				1,272
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income				24.6
Balance at Mar. 31, 2014
Balance at Dec. 31, 2013				1,272			1,272							0	0	0			0			1,272			0
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income				80.6			80.6							0	0	0			0			80.6			0
Contributions from Dominion				259.9			259.9							0	0	0			0			259.9			0
Balance at Oct. 19, 2014
Balance at Dec. 31, 2013				1,272
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income		106.9		106.9
Balance at Dec. 31, 2014		2,150.80
Balance at Oct. 19, 2014
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income	[1]	26.3			0			3		1.8		4.7					0			9.5			16.8
Contributions from Dominion			0			-655.3			0		204.2		451.1					0			0			0
Formation and Offering Transactions:
Allocation of predecessor member's equity to noncontrolling interest			0			-957.2			0		0		0					0			-957.2			957.2
Settlement of net current and deferred income tax liabilities			147.9			0			0		18.7		41.4					0			60.1			87.8
Additional basis in property, plant and equipment received from Dominion			23.2			0			0		2.9		6.6					0			9.5			13.7
Issuance of common units, net of offering costs			392.4			0			392.4		0		0					0			392.4			0
Distributions			-51.5			0			0		-13.9		-37.6					0			-51.5			0
Balance at Dec. 31, 2014		$2,150.80			$0			$395.40		$213.70		$466.20					$0			$1,075.30			$1,075.50
[1]	Allocation of net income attributable to partners' ownership interest subsequent to initial public offering has been adjusted for rounding.

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012
Operating Activities
Net Income including noncontrolling interest	$106.90
Adjustments to reconcile net income including noncontrolling interest to net cash provided by operating activities:
Depreciation and amortization	37.7
Deferred income taxes	13.1	[1]
Changes in:
Customer and other receivables	0.1
Affiliated receivables	-1.4
Prepayments	-4.6
Accounts payable	0.3
Payables to affiliates	1.9
Accrued payroll and taxes	1.2
Other operating assets and liabilities	0.9
Net cash provided by operating activities	156.1
Investing Activities
Plant construction and other property additions	-572.2
Other	0.6
Net cash used in investing activities	-571.6
Financing Activities
Issuance (repayment) of affiliated current borrowings, net	0
Contributions from Dominion	238.7
Net proceeds from issuance of common units	392.5
Advance from affiliate	0
Distribution to Dominion	-51.5
Other	0
Net cash provided by (used in) financing activities	579.7
Increase in cash and cash equivalents	164.2
Cash and cash equivalents at beginning of period	11.2
Cash and cash equivalents at end of period	175.4
Supplemental Cash Flow Information
Income taxes	38.6
Significant noncash investing and financing activities:
Accrued capital expenditures	6.7
Conversion of affiliated current borrowings to payables to affiliates	0
Increase in property, plant and equipment from CPCN obligation
Significant noncash investing and financing activities:
Accrued capital expenditures	44.1
Additional basis in property, plant and equipment received from Dominion
Significant noncash investing and financing activities:
Contribution from affiliate	23.2
Settlement of net current and deferred income tax liabilities
Significant noncash investing and financing activities:
Contribution from affiliate	147.9
Equity contribution from Dominion to relieve payables to affiliates
Significant noncash investing and financing activities:
Contribution from affiliate	20
Equity contribution from Dominion to relieve affiliated current borrowings
Significant noncash investing and financing activities:
Contribution from affiliate	0
Equity contribution from Dominion related to income taxes prior to the Offering
Significant noncash investing and financing activities:
Contribution from affiliate	1.2
Predecessor
Operating Activities
Net Income including noncontrolling interest	106.9		109.4	97.2
Adjustments to reconcile net income including noncontrolling interest to net cash provided by operating activities:
Depreciation and amortization			31.7	33.3
Deferred income taxes			7.3	22.1
Changes in:
Customer and other receivables			0.2	0.9
Affiliated receivables			-4.5	1.4
Prepayments			-8	0
Accounts payable			-4.7	-0.6
Payables to affiliates			1.2	-1.8
Accrued payroll and taxes			-5.9	-1.4
Other operating assets and liabilities			9.5	3.8
Net cash provided by operating activities			136.2	154.9
Investing Activities
Plant construction and other property additions			-294.6	-51.1
Other			-0.2	-0.2
Net cash used in investing activities			-294.8	-51.3
Financing Activities
Issuance (repayment) of affiliated current borrowings, net			149.8	-42
Contributions from Dominion			0	0
Net proceeds from issuance of common units			0	0
Advance from affiliate			20	0
Distribution to Dominion			0	-61.7
Other			0	0.1
Net cash provided by (used in) financing activities			169.8	-103.6
Increase in cash and cash equivalents			11.2	0
Cash and cash equivalents at beginning of period	11.2		0	0
Cash and cash equivalents at end of period			11.2	0
Supplemental Cash Flow Information
Income taxes			52.6	42.1
Significant noncash investing and financing activities:
Accrued capital expenditures			8.4	6.4
Conversion of affiliated current borrowings to payables to affiliates			0	100.9
Predecessor | Increase in property, plant and equipment from CPCN obligation
Significant noncash investing and financing activities:
Accrued capital expenditures			0	0
Predecessor | Additional basis in property, plant and equipment received from Dominion
Significant noncash investing and financing activities:
Contribution from affiliate			0	0
Predecessor | Settlement of net current and deferred income tax liabilities
Significant noncash investing and financing activities:
Contribution from affiliate			0	0
Predecessor | Equity contribution from Dominion to relieve payables to affiliates
Significant noncash investing and financing activities:
Contribution from affiliate			100.9	0
Predecessor | Equity contribution from Dominion to relieve affiliated current borrowings
Significant noncash investing and financing activities:
Contribution from affiliate			360	0
Predecessor | Equity contribution from Dominion related to income taxes prior to the Offering
Significant noncash investing and financing activities:
Contribution from affiliate			$3.20	$3.40
[1]	Income taxes recognized prior to the Offering.

Description_of_Business_and_Ba

Description of Business and Basis of Presentation	12 Months Ended
	Dec. 31, 2014
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 on March 11, 2014 by Dominion MLP Holding Company, LLC and Dominion Midstream GP, LLC, both indirect wholly-owned subsidiaries of Dominion, to acquire the Preferred Equity Interest and non-economic general partner interest in Cove Point from Dominion. On October 20, 2014, Dominion Midstream completed the Offering of 20,125,000 common units (including 2,625,000 common units issued pursuant to the exercise of the underwriters' over-allotment option) representing limited partner interests. A registration statement on Form S-1, as amended through the time of its effectiveness, was filed by Dominion Midstream with the SEC and was declared effective on October 10, 2014. See Note 2 for information regarding the closing of the Offering.
	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 will be made on a quarterly basis and will not be cumulative. Until the Liquefaction Project is completed, Cove Point is prohibited from making a distribution on its common equity interests until it has a distribution reserve sufficient to pay two quarters of Preferred Return Distributions. The Preferred Equity Interest is also entitled to the Additional Return Distributions.
	Cove Point is the owner and operator of the Cove Point LNG Facility and the Cove Point Pipeline. The Cove Point LNG Facility is an LNG import/regasification and storage facility located on the Chesapeake Bay in Lusby, Maryland.
	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. Dominion Midstream owns the general partner interest and controls Cove Point 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.
	For the periods prior to the closing of the Offering on October 20, 2014, the financial statements included in this Annual Report on Form 10-K were derived from the financial statements and accounting records of Cove Point as our predecessor. The financial statements were prepared using Dominion's historical basis in the assets and liabilities of Cove Point and include all revenues, costs, assets and liabilities attributed to Cove Point.
	For the period subsequent to the closing of the Offering, the Consolidated Financial Statements represent the consolidated results of operations, financial position and cash flows of Dominion Midstream.
	•	The consolidated statements of income and cash flows for the year ended December 31, 2014, consist of the consolidated results of Dominion Midstream for the period from October 20, 2014 through December 31, 2014, and the results of our Predecessor for the period from January 1, 2014, through October 19, 2014.
	•	The consolidated balance sheet at December 31, 2014, consists of the consolidated balances of Dominion Midstream.
	•	The consolidated statement of equity and partners' capital for the year ended December 31, 2014, consists of both the activity for our Predecessor prior to October 20, 2014, and the consolidated activity for Dominion Midstream completed at and subsequent to the Offering on October 20, 2014.
	The financial statements for all years presented include costs for certain general, administrative and corporate expenses assigned by DRS to Dominion Midstream and Cove Point on the basis of direct and allocated methods in accordance with Dominion Midstream and Cove Point's services agreements with DRS. Where costs incurred cannot be determined by specific identification, the costs are allocated based on the proportional level of effort devoted by DRS resources that is attributable to the entities, determined by reference to number of employees, salaries and wages and other similar measures for the relevant DRS department. Management believes the assumptions and methodologies underlying the allocation of general corporate overhead expenses are reasonable. Nevertheless, the Consolidated Financial Statements prior to the Offering may not include all of the actual expenses that would have been incurred had we been a stand-alone publicly traded partnership during the periods presented, and may not reflect our actual results of operations, financial position and cash flows had we been a stand-alone publicly traded partnership during the periods prior to the Offering.
	Dominion Midstream reports one operating segment, Dominion Energy, which consists of LNG import, transportation and storage. In addition to the Dominion Energy operating segment, Dominion Midstream also reports a Corporate and Other segment, which primarily includes specific items attributable to its operating segment that are not included in profit measures evaluated by executive management in assessing the segment's performance. See Note 17 for further discussions of Dominion Midstream's operating segment.

Initial_Public_Offering

Initial Public Offering	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Initial Public Offering	INITIAL PUBLIC OFFERING
	On October 15, 2014, Dominion Midstream's common units began trading on the NYSE under the ticker symbol "DM." On October 20, 2014, Dominion Midstream closed the Offering of 20,125,000 common units to the public at a price of $21.00 per common unit, which included a 2,625,000 common unit over-allotment option that was exercised in full by the underwriters.
	In exchange for Dominion's contribution of the general partner interest in Cove Point and a portion of the Preferred Equity Interest to us, which we contributed to Cove Point Holdings, Dominion received:
	•	11,847,789 common units and 31,972,789 subordinated units, representing an aggregate 68.5% limited partner interest;
	•	All of our IDRs;
	•	A non-economic general partner interest; and
	•	A cash distribution of $51.5 million as described in the partnership agreement.
	Dominion Midstream received net proceeds of $392.4 million from the sale of 20,125,000 common units, after deducting underwriting discounts, structuring fees and offering expenses of $30.2 million, which were allocated to the public common units. Dominion Midstream utilized $340.9 million of net proceeds to make, through Cove Point Holdings, a contribution to Cove Point in exchange for the remaining portion of the Preferred Equity Interest.
	Reconciliation of Cash Proceeds
	(millions)
	Total proceeds from the Offering	$	422.6
	Less: Underwriting discounts, structuring fees and offering expenses	(30.2		)
	Net proceeds from the Offering	392.4
	Less: Contribution to Cove Point for remaining portion of Preferred Equity Interest	340.9
	Net proceeds distributed to Dominion from the Offering	$	51.5
	Additional information pertaining to the transactions effected at the closing of the Offering on October 20, 2014 is provided as follows:
	•	Dominion's contribution of the general partner interest in Cove Point and a portion of the Preferred Equity Interest to us was an exchange of ownership interests between 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. Dominion's interest in Cove Point is reflected as noncontrolling interest equity of Dominion Midstream. The equity attributable to the noncontrolling interest is calculated based on the predecessor historical parent net equity adjusted for the transactions effected at the closing of the Offering.
	•	In connection with the termination of Cove Point's participation in Dominion's intercompany tax sharing agreement, the settlement of Cove Point's obligations related to existing federal and state income tax payables, receivables and deferred income taxes is reflected as an equity transaction in the Consolidated Financial Statements. Beginning October 20, 2014, Dominion Midstream, as a pass-through entity, is generally not subject to income taxes.
	•	Dominion Midstream recorded additional basis in Dominion's equity interests in Cove Point not reflected on the predecessor financial statements. This increase in basis relates to additional capitalized interest that was limited at Cove Point to actual interest incurred but is reflected in Dominion’s basis in Cove Point’s property, plant and equipment. Since this transaction was an exchange of ownership interest between entities under common control, Dominion Midstream’s basis equals Dominion’s historical basis.

Significant_Accounting_Policie

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Significant Accounting Policies	SIGNIFICANT ACCOUNTING POLICIES
	General
	Dominion Midstream makes certain estimates and assumptions in preparing its 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, expenses, and cash flows for the periods presented. Actual results may differ from those estimates.
	Dominion Midstream's Consolidated Financial Statements include, after eliminating intercompany transactions and balances, the accounts of their respective majority-owned subsidiaries.
	Dominion Midstream reports certain contracts and instruments at fair value. The carrying values of customer and affiliated receivables, payables to affiliates and accounts payable are estimated to be substantially the same as their fair values at December 31, 2014 and 2013.
	Cove Point participated in Dominion's intercompany tax sharing agreement prior to the Offering. See Note 15 for further information on accounting for income taxes.
	Cove Point participates in certain Dominion-sponsored pension and other postretirement benefit plans. See Note 10 for further information on these plans.
	Operating Revenue
	Operating revenue is recorded on the basis of services rendered, commodities delivered or contracts settled and includes amounts yet to be billed to customers. Cove Point is currently generating significant revenue and earnings from annual reservation payments under long-term regasification, firm peaking storage and firm transportation contracts. Customer receivables at December 31, 2014 and 2013 included $19.9 million and $20.0 million, respectively, of accrued unbilled revenue based on estimated amounts of natural gas delivered but not yet billed to its customers.
	Cove Point renegotiated certain import-related contracts which will result in annual payments in the years 2013 through 2017 totaling approximately $50 million. Deferred revenue represents the difference between the amount received and the revenue recognized.
	The primary types of sales and service activities reported as operating revenue are as follows:
	•	Gas transportation and storage revenue consists primarily of storage services and transmission services; and
	•	Other revenue consists primarily of sales of purchased gas retained for use in routine operations and LNG cargos and the renegotiated contract payments described above.
	Purchased Gas - Deferred Costs
	The difference between purchased gas expenses and the related levels of recovery for these expenses in current rates are deferred and matched against recoveries in future periods. The deferral of costs in excess of current period fuel rate recovery is recognized as a regulatory asset, while rate recovery in excess of current period fuel expenses is recognized as a regulatory liability.
	Income Taxes
	Dominion Midstream is organized as an MLP. As a pass-through entity for U.S. federal and state income tax purposes, each of its unitholders 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. Income before taxes, as determined under GAAP, may differ significantly from taxable income reportable to unitholders. Such differences may result from different bases of assets and liabilities and timing of recognition for income, gains, losses and expenditures for tax and financial reporting purposes, as well as the taxable income allocation requirements under the partnership agreement.
	As an MLP, at least 90% of Dominion Midstream’s total gross income must constitute qualifying income, determined on a calendar year basis under applicable income tax law. If the amount of qualifying income does not satisfy this requirement, Dominion Midstream would be taxed as a corporation. For the period October 20, 2014, through December 31, 2014, Dominion Midstream’s qualifying income exceeded the required amount. The Consolidated Financial Statements reflect management’s conclusion that Dominion Midstream’s status as a pass-through entity, if examined, would be sustained based on the technical merits of applicable tax law.
	Prior to the Offering, Cove Point was not a separate taxable entity for U.S. federal and state income tax purposes. Cove Point’s business activities were included in the consolidated U.S. federal income tax return filed by Dominion and its subsidiaries, DCPI’s Maryland state income tax returns and combined Virginia income tax returns filed by Dominion and certain subsidiaries. With Dominion Midstream’s acquisition of the Preferred Equity Interest and the general partnership interest in Cove Point, Cove Point is now treated as a limited partnership, a pass-through entity for U.S. federal and state income tax purposes. Dominion Midstream’s Consolidated Financial Statements reflect Cove Point’s income taxes for the period prior to the Offering.
	Cove Point’s current income taxes were based on taxable income or loss, determined on a separate company basis, and, where applicable, settled in accordance with the principles of Dominion’s intercompany tax sharing agreement. Deferred income tax assets and liabilities were provided, representing future effects on income taxes for temporary differences between the bases of assets and liabilities for financial reporting and tax purposes. Accordingly, deferred taxes were recognized for the future consequences of different treatments used for the reporting of transactions in financial accounting and income tax returns. In addition, a valuation allowance was established when it was more-likely-than-not that all, or a portion, of a deferred tax asset would not be realized. Where the treatment of temporary differences was different for rate-regulated operations, a regulatory asset was recognized if it is probable that future revenues would be provided for the payment of deferred tax liabilities. Reported amounts of assets and liabilities exceeded tax bases by $386.4 million at December 31, 2014.
	Judgment and the use of estimates are required in developing the provision for income taxes and reporting of tax-related assets and liabilities. The interpretation of tax laws involves uncertainty, since tax authorities may interpret the laws differently. For periods in which income taxes are included, a position taken, or expected to be taken, in income tax returns is recognized only if it is more-likely-than-not to be realized, assuming that the position will be examined by tax authorities with full knowledge of all relevant information. If it is not more-likely-than-not that a tax position, or some portion thereof, will be sustained, the related tax benefits are not recognized in the financial statements. Unrecognized tax benefits may result in an increase in income taxes payable, a reduction of income tax refunds receivable or changes in deferred taxes. Also, when uncertainty about the deductibility of an amount is limited to the timing of such deductibility, the increase in income taxes payable (or reduction in tax refunds receivable) is accompanied by a decrease in deferred tax liabilities. Except when such amounts are presented net with amounts receivable from or amounts prepaid to tax authorities, noncurrent income taxes payable related to unrecognized tax benefits are classified in other deferred credits and other liabilities and current payables are included in accrued interest, payroll and taxes on the Consolidated Balance Sheets.
	Under Dominion’s tax sharing agreement, payments of federal and state income taxes of $38.6 million, $52.6 million and $42.1 million were made to Dominion and DCPI for the years ended December 31, 2014, 2013 and 2012, respectively. The settlement of Cove Point’s obligations related to existing federal and state net income tax payables and deferred income taxes at the time of the Offering is reflected as an equity contribution in Dominion Midstream’s Consolidated Financial Statements.
	Interest accrued on uncertain tax positions is included in interest expense or income, as applicable. No penalties were accrued and interest expense was not material in all years presented.
	Cash and Cash Equivalents
	Current banking arrangements generally do not require checks to be funded until they are presented for payment. At December 31, 2014 and 2013, accounts payable included $0.4 million and $0.2 million, respectively, of checks outstanding but not yet presented for payment. For purposes of the Balance Sheets and Statements of Cash Flows, cash and cash equivalents include cash on hand, cash in banks and temporary investments purchased with an original maturity of three months or less.
	Property, Plant and Equipment
	Property, plant and equipment, including additions and replacements is recorded at original cost, consisting of labor and materials and other costs such as asset retirement costs, capitalized interest and, for certain operations subject to cost-of-service rate regulation, AFUDC and overhead costs. The cost of repairs and maintenance, including minor additions and replacements, is charged to expense as it is incurred.
	In 2014, Dominion Midstream capitalized AFUDC of $0.1 million to property, plant and equipment. In 2013 and 2012, Dominion Midstream capitalized interest costs and AFUDC of $0.7 million and $1.3 million, respectively, to property, plant and equipment.
	For property subject to cost-of-service rate regulation, the undepreciated cost of such property, less salvage value, is generally charged to accumulated depreciation at retirement. Cost of removal collections not representing AROs are recorded as regulatory liabilities.
	For property that is not subject to cost-of-service rate regulation, cost of removal not associated with AROs is charged to expense as incurred. Dominion Midstream also records gains and losses upon retirement based upon the difference between the proceeds received, if any, and the property’s net book value at the retirement date.
	Depreciation of property, plant and equipment is computed on the straight-line method based on projected service lives. Depreciation rates on utility property, plant and equipment are as follows:
	Year Ended December 31,	2014	2013	2012
	(percent)
	Storage	2.39	2.43	2.6
	Transmission	2.81	2.83	2.83
	General and other	4.09	3.71	5.35
	In 2014, Cove Point shortened the useful life of assets expected to be retired as a result of commencement of construction on the generating station associated with the Liquefaction Project, which resulted in an increase to depreciation expense of $6.2 million. In 2013, Cove Point extended the useful life of existing expansion assets by nine years as a result of the Liquefaction Project, which resulted in a decrease to depreciation expense of $1.5 million ($1.0 million after tax).
	Long-Lived and Intangible Assets
	Dominion Midstream performs an evaluation for impairment whenever events or changes in circumstances indicate that the carrying amount of long-lived assets or intangible assets with finite lives may not be recoverable. A long-lived or intangible asset is written down to fair value if the sum of its expected future undiscounted cash flows is less than its carrying amount. Intangible assets with finite lives are amortized over their estimated useful lives.
	Regulatory Assets and Liabilities
	For regulated businesses subject to FERC cost-of-service rate regulation, regulatory practices that assign costs to accounting periods may differ from accounting methods generally applied by nonregulated companies. When it is probable that the FERC will permit the recovery of current costs through future rates charged to customers, these costs that otherwise would be expensed by nonregulated companies are deferred as regulatory assets. Likewise, regulatory liabilities are recognized when it is probable that the FERC will require customer refunds through future rates or when revenue is collected from customers for expenditures that have yet to be incurred. Generally, regulatory assets and liabilities are amortized into income over the period authorized by the FERC.
	Dominion Midstream evaluates whether or not recovery of its regulatory assets through future rates is probable and makes various assumptions in its analyses. The expectations of future recovery are generally based on orders issued by the FERC or historical experience, as well as discussions with the FERC. If recovery of a regulatory asset is determined to be less than probable, it will be written off in the period such assessment is made.
	Materials and Supplies
	Materials and supplies are valued primarily using the weighted-average cost method.
	Natural Gas Imbalances
	Natural gas imbalances occur when the physical amount of natural gas delivered from, or received by, a pipeline system or storage facility differs from the contractual amount of natural gas delivered or received. Dominion Midstream values these imbalances due to, or from, shippers and operators at an appropriate index price at period end, subject to the terms of its tariff for regulated entities. Imbalances are primarily settled in-kind. Imbalances due to Dominion Midstream from other parties are reported as current assets and imbalances that Dominion Midstream owes to other parties are reported as current liabilities in the Consolidated Balance Sheets.
	Goodwill
	Dominion Midstream evaluates goodwill for impairment annually as of April 1 and whenever an event occurs or circumstances change in the interim that would more-likely-than-not reduce the fair value of its reporting unit below its carrying value.

Net_Income_Per_Unit

Net Income Per Unit	12 Months Ended
	Dec. 31, 2014
Earnings Per Share [Abstract]
Net Income Per Unit	NET INCOME PER UNIT
	Net income per unit applicable to common limited partner units and to subordinated limited partner units is computed by dividing the respective limited partners’ interest in net income attributable to Dominion Midstream, after deducting any 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, and IDRs.
	Dominion Midstream’s net income is allocated to the limited partners in accordance with their respective partnership percentages, after giving effect to priority income allocations for 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 limited partners 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 unit.
	Net income per unit is only calculated for the periods subsequent to the Offering as no units were outstanding prior to October 20, 2014. Diluted net income per unit is the same as basic net income per unit as there were no potentially dilutive common or subordinated units outstanding as of December 31, 2014.
	The calculation of earnings per unit is as follows:
	Year Ended December 31,	2014
	(millions)
	Net income attributable to limited partners subsequent to initial public offering	$	9.5
	Less distributions declared on(1):
	Incentive distribution holder rights(2)	—
	Common unitholders(3)	4.5
	Subordinated unitholder(3)	4.4
	Total distributions declared	8.9
	Undistributed earnings	$	0.6
	-1	On January 23, 2015, the Board of Directors of our general partner declared a prorated initial quarterly cash distribution of $0.1389 per unit, totaling $8.9 million, for the period subsequent to the Offering. This distribution was paid on February 13, 2015 to unitholders of record on February 3, 2015. The initial quarterly cash distribution was calculated as the minimum quarterly distribution of $0.1750 per unit prorated for the portion of the quarter subsequent to the Offering.
	-2	Dominion is a non-economic general partner that holds all of the IDRs.
	-3	Allocation of distributions declared has been adjusted for rounding.
	Basic and diluted net income subsequent to initial public offering per unit
		Common Units		Subordinated Units		Total
	(millions, except for weighted average units and per unit data)
	Distributions declared(1)	$	4.5	$	4.4	$	8.9
	Undistributed earnings	0.3		0.3		0.6
	Net income attributable to limited partners subsequent to initial public offering	$	4.8	$	4.7	$	9.5
	Weighted average units outstanding	31,975,079		31,972,789		63,947,868
	Net income per unit	$	0.15	$	0.15	$	0.15
	-1	Allocation of distributions declared has been adjusted for rounding.

Operating_Revenue

Operating Revenue	12 Months Ended
	Dec. 31, 2014
Revenue Recognition [Abstract]
Operating Revenue	OPERATING REVENUE
	Operating revenue consists of the following:
	Year Ended December 31,	2014		2013		2012
	(millions)
	Gas transportation and storage	$	257.2	$	256.5	$	255.8
	Other	56.1		87		37.2
	Total operating revenue	$	313.3	$	343.5	$	293

Property_Plant_and_Equipment

Property Plant and Equipment	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	PROPERTY, PLANT AND EQUIPMENT
	Major classes of property, plant and equipment and their respective balances for Dominion Midstream are as follows:
	At December 31,	2014		2013
	(millions)
	Storage	$	882	$	869.1
	Transmission	323.9		319.3
	Plant under construction	972.3		352.7
	General and other	24.9		24.6
	Total property, plant and equipment	$	2,203.10	$	1,565.70

Goodwill_and_Intangible_Assets

Goodwill and Intangible Assets	12 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	GOODWILL AND INTANGIBLE ASSETS
	Goodwill
	There have been no changes in Dominion Midstream's carrying amount and segment allocation of goodwill as presented below:
		Dominion Energy		Corporate and Other		Total
	(millions)
	Balance at December 31, 2012(1)	$	45.9	$	—	$	45.9
	No events affecting goodwill	—		—		—
	Balance at December 31, 2013(1)	$	45.9	$	—	$	45.9
	No events affecting goodwill	—		—		—
	Balance at December 31, 2014(1)	$	45.9	$	—	$	45.9
	-1	There are no accumulated impairment losses.
	Other Intangible Assets
	Dominion Midstream's other intangible assets are subject to amortization over their estimated useful lives. Dominion Midstream's amortization expense for intangible assets was $0.6 million, $0.6 million and $0.7 million in 2014, 2013 and 2012, respectively. In both 2014 and 2013, Dominion Midstream acquired $0.2 million of intangible assets, primarily representing software with estimated weighted-average amortization periods of approximately 5 and 10 years, respectively. The components of intangible assets are as follows:
	At December 31,	2014				2013
		Gross		Accumulated		Gross		Accumulated
		Carrying		Amortization		Carrying		Amortization
		Amount				Amount
	(millions)
	Software and other	$	6.5	$	2.4	$	6.5	$	2.1
	Licenses	11		3		11		2.9
	Total	$	17.5	$	5.4	$	17.5	$	5
	Annual amortization expense for these intangible assets is estimated to be as follows:
		2015		2016		2017		2018		2019
	(millions)
		$	0.5	$	0.5	$	0.5	$	0.5	$	0.5

Regulatory_Assets_and_Liabilit

Regulatory Assets and Liabilities	12 Months Ended
	Dec. 31, 2014
Regulated Operations [Abstract]
Regulatory Assets and Liabilities	REGULATORY ASSETS AND LIABILITIES
	Regulatory assets and liabilities include the following:
	At December 31,	2014		2013
	(millions)
	Regulatory assets:
	Unrecovered gas costs(1)	$	1.5	$	5.4
	Other	0.2		0.1
	Regulatory assets-current	1.7		5.5
	Income taxes recoverable through future rates(2)	2.5		2.5
	Regulatory assets-non-current	2.5		2.5
	Total regulatory assets	$	4.2	$	8
	Regulatory liabilities:
	Overrecovered gas costs(1)	$	0.5	$	0.8
	LNG cargo obligations(3)	3		6.7
	Other	0.1		0.2
	Regulatory liabilities-current	3.6		7.7
	Provision for future cost of removal(4)	33		29.5
	Other	0.5		0.9
	Regulatory liabilities-non-current	33.5		30.4
	Total regulatory liabilities	$	37.1	$	38.1
	-1	Reflects unrecovered/overrecovered gas costs at Cove Point, which are subject to annual filings with the FERC.
	-2	Amounts to be recovered through future rates to provide for income taxes that become payable by unitholders when rate revenue is provided to recover AFUDC-equity when such amounts are recovered through book depreciation.
	-3	Represents obligations to the Import Shippers for LNG cargo received. See Note 9 for further information.
	-4	Rates charged to customers by Cove Point include a provision for the cost of future activities to remove assets that are expected to be incurred at the time of retirement.
	At December 31, 2014 and 2013, approximately $1.7 million and $5.5 million, respectively, of regulatory assets represented past expenditures on which Cove Point does not currently earn a return. These expenditures are expected to be recovered within one year.

Regulatory_Matters

Regulatory Matters	12 Months Ended
	Dec. 31, 2014
Regulated Operations [Abstract]
Regulatory Matters	REGULATORY MATTERS
	The 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, the FERC has authority over rates, terms and conditions of services performed by Cove Point. The FERC also has jurisdiction over siting, construction and operation of natural gas import facilities and interstate natural gas pipeline facilities.
	In May 2011, Cove Point filed a general rate case for its FERC jurisdictional services, with proposed rates to be effective July 2011.  In July 2012, the FERC issued an order approving a stipulation and agreement among Cove Point, the FERC trial staff and the other active parties in the rate case resolving all issues set for hearing by the FERC and establishing the mechanism for operational purchases of LNG, with settlement rates effective April 2012.  Pursuant to the terms of the settlement, future operational purchases of LNG are not expected to affect Cove Point’s net results of operations.  Cove Point and settling customers are subject to a rate moratorium through December 31, 2016.  Cove Point is required to file its next rate case in 2016 with rates to be effective January 1, 2017.
	In April 2013, Cove Point filed its application with the FERC requesting authorization to construct, modify and operate the Liquefaction Project, as well as enhance the Cove Point Pipeline. In May 2014, the FERC staff issued its EA for the Liquefaction Project. In the EA, the FERC staff addressed a variety of topics related to the proposed construction and development of the Liquefaction Project and its potential impact to the environment, including in the areas of geology, soils, groundwater, surface waters, wetlands, vegetation, wildlife and aquatic resources, special status species, land use, recreation, socioeconomics, air quality and noise, reliability and safety, and cumulative impacts. Based on the analysis in the EA, the FERC staff determined that with the implementation of appropriate mitigation measures in these areas, the Liquefaction Project can be built and operated safely with no significant impact to the environment. In September 2014, the FERC Order was issued authorizing the Liquefaction Project. In October 2014, several parties filed a motion with the FERC to stay the FERC Order and requested rehearing. The FERC Order remains in effect pending consideration of the motion by the FERC.

Employee_Benefit_Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Employee Benefit Plans	EMPLOYEE BENEFIT PLANS
	Defined Benefit Plans
	Cove Point participates in retirement benefit plans sponsored by Dominion, which provide certain retirement benefits to eligible active employees, retirees and qualifying dependents of Cove Point. Under the terms of its benefit plans, Dominion reserves the right to change, modify or terminate the plans. From time to time in the past, benefits have changed, and some of these changes have reduced benefits.
	Pension benefits for Cove Point employees are covered by the Dominion Pension Plan, a defined benefit pension plan sponsored by Dominion that provides benefits to multiple Dominion subsidiaries. Retirement benefits payable are based primarily on years of service, age and the employee's compensation. As a participating employer, Cove Point is subject to Dominion's funding policy, which is to contribute annually an amount that is in accordance with the provisions of ERISA. During 2014, Cove Point made no contributions to the Dominion Pension Plan, and no contributions to this plan are currently expected in 2015. Net periodic pension cost related to this plan was $1.1 million, $1.4 million and $1.1 million in 2014, 2013 and 2012, respectively, recorded in other operations and maintenance expense in the Consolidated Statements of Income. The funded status of various Dominion subsidiary groups and employee compensation are the basis for determining the share of total pension costs for participating Dominion subsidiaries. At December 31, 2014 and 2013, amounts due to Dominion associated with this plan, were $3.5 million and $2.5 million, respectively, recorded in pension and other postretirement benefit liabilities on the Consolidated Balance Sheets.
	Retiree healthcare and life insurance benefits for Cove Point employees are covered by the Dominion Retiree Health and Welfare Plan, a plan sponsored by Dominion that provides certain retiree healthcare and life insurance benefits to multiple Dominion subsidiaries. Annual employee premiums are based on several factors such as age, retirement date and years of service. Net periodic benefit (credit) cost related to this plan was $(0.4) million, $0.1 million and $0.2 million for 2014, 2013 and 2012, respectively, recorded in other operations and maintenance expense in the Consolidated Statements of Income. Employee headcount is the basis for determining the share of total other postretirement benefit costs for participating Dominion subsidiaries. At December 31, 2014 and 2013, liabilities to Dominion associated with this plan were $0.9 million and $1.6 million, respectively, recorded in pension and other postretirement benefit liabilities on the Consolidated Balance Sheets.
	Dominion holds investments in trusts to fund employee benefit payments for the pension and other postretirement benefit plans in which Cove Point's employees participate. Any investment-related declines in these trusts will result in future increases in the net periodic cost recognized for such employee benefit plans and will be included in the determination of the amount of cash that Cove Point will provide to Dominion for its share of employee benefit plan contributions.
	Defined Contribution Plans
	Cove Point also participates in Dominion-sponsored defined contribution employee savings plans that cover multiple Dominion subsidiaries. Cove Point recognized expense of $0.2 million in other operations and maintenance expense in the Consolidated Statements of Income during each year of 2014, 2013 and 2012, as employer matching contributions to these plans.

CPCN_Obligation

CPCN Obligation	12 Months Ended
	Dec. 31, 2014
Other Liabilities Disclosure [Abstract]
CPCN Obligation	CPCN OBLIGATION
	In April 2013, Cove Point filed an application with the Maryland Commission requesting authorization to construct a generating station in connection with the Liquefaction Project. In May 2014, the Maryland Commission granted the CPCN authorizing the construction of such generating station. The CPCN obligates Cove Point to make payments totaling approximately $48.0 million. These payments consist of $40.0 million to the SEIF over a five-year period beginning in 2015 and $8.0 million to Maryland low income energy assistance programs over a twenty-year period expected to begin in 2018. In December 2014, upon receipt of applicable approvals to commence construction of the generating station, Dominion Midstream recorded the present value of the obligation as an increase to property, plant and equipment and a corresponding liability for these future payments using an effective interest rate of 1.9%.
	In June 2014, a party filed a notice of petition for judicial review of the CPCN with the Circuit Court for Baltimore City in Maryland. In September 2014, the party filed with the Maryland Commission a motion to stay the CPCN pending judicial review of the CPCN.  In December 2014, the Circuit Court issued an order affirming the Maryland Commission’s grant of the CPCN and dismissing the appeal, and the motion for stay was denied by the Maryland Commission. In January 2015, the same party filed a Notice of Appeal of the Baltimore Circuit Court’s Order affirming the Maryland Commission’s grant of the CPCN with the Court of Special Appeals for the Circuit Court of Baltimore City.

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2014
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 the 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.
	Decommissioning Costs
	Under the terms of the 2005 Agreement with the Sierra Club and the Maryland Conservation Council, Inc., Cove Point would be responsible for certain onshore and offshore site restoration activities at the Cove Point site only if it voluntarily tenders title according to the terms of this agreement. As Cove Point is permitted to operate the Cove Point LNG Facility for an indefinite time period and currently has no plans to voluntarily tender title, Cove Point does not have sufficient information to determine a reasonable range of settlement dates for decommissioning and therefore has not recorded a liability.
	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 December 31, 2014, Cove Point had purchased $10.8 million of surety bonds. Under the terms of surety bonds, Cove Point is obligated to indemnify the respective surety bond company for any amounts paid.

Credit_Risk

Credit Risk	12 Months Ended
	Dec. 31, 2014
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.
	Cove Point provides service to twenty-three customers, including the Storage Customers, sixteen marketers or end users and the Import Shippers. The three largest customers comprised approximately 93%, 94% and 93% of the total transportation and storage revenues for the years ended December 31, 2014, 2013 and 2012, respectively. Cove Point's largest customer represented approximately 72% of such amounts in 2014, 2013 and 2012. Cove Point has not experienced any credit losses in connection with its trade receivables. The majority of services are provided under long-term contracts at FERC-approved rates.

Related_Party_Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2014
Related Party Transactions [Abstract]
Related Party Transactions	RELATED-PARTY TRANSACTIONS
	Dominion Midstream engages in related-party transactions primarily with other Dominion subsidiaries (affiliates). 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 10. A discussion of the significant related party transactions follows.
	Transactions with Affiliates
	In connection with the Offering, our general partner entered into a services agreement with DRS. DRS provides administrative, management and other services to Dominion and its subsidiaries as a subsidiary service company. From time to time and at the option of our general partner, our general partner will request that DRS provide, and reimburse DRS for the cost of providing, such administrative, management and other services as it deems necessary or appropriate for our operations. We will reimburse our general partner and its affiliates for the associated costs of obtaining these services.
	In addition, Cove Point provides transportation services to affiliates and affiliates provide goods and services to Cove Point. The affiliated transactions are presented below:
	Year Ended December 31,	2014		2013		2012
	(millions)
	Sales of natural gas transportation services to affiliates	$	2.4	$	2.3	$	2.1
	Purchased gas from affiliates	0.6		0.7		—
	Services provided by DRS(1)(2)	12.3		9.3		6.1
	Goods and services provided by affiliates to Cove Point(1)	3.8		3.2		3
	-1	Includes $6.7 million, $4.8 million and $2.1 million of capitalized expenditures in 2014, 2013 and 2012, respectively.
	-2	Dominion Midstream determined that neither it nor Cove Point is the most closely associated entity with DRS, an affiliated variable interest entity, and therefore neither is the primary beneficiary. DRS provides accounting, legal, finance and certain administrative and technical services to all Dominion subsidiaries, including Dominion Midstream and Cove Point. Neither Dominion Midstream nor Cove Point has an obligation to absorb more than its allocated share of DRS costs.
	Advance from Affiliate
	During 2013, Cove Point received an advance from an affiliate of $20.0 million. This amount is included within payables to affiliates at December 31, 2013 and was converted to an equity contribution in March 2014. During 2013, $100.9 million of payables to affiliates were converted to an equity contribution.
	Dominion Credit Facility
	In connection with the Offering, Dominion Midstream entered into a credit facility with Dominion with a borrowing capacity of $300 million. The facility was undrawn at December 31, 2014. A summary of certain key terms of the credit facility with Dominion is as follows:
	•	No upfront commitment fee in order to enter into the facility, and no ongoing facility or similar charges assessed against undrawn amounts.
	•	Five-year term, with only interest payments on any drawn amounts payable prior to maturity or acceleration.
	•	Interest payments on any drawn balances are due on a quarterly basis and amounts drawn accrue interest at variable interest rates, determined based on our ratio of total debt to Adjusted EBITDA or, if we obtain long-term debt credit ratings in the future, based on such credit ratings in effect from time to time.
	•
	•	Amounts then due and payable under the credit facility will need to be satisfied prior to making any distributions to unitholders. The credit facility does not include any other financial tests, covenants or conditions that must be satisfied as a condition to making distributions for so long as the facility remains in place.
	•	The credit facility contains limited representations, warranties and ongoing covenants consistent with other credit facilities made available by Dominion to certain of its other affiliates.
	•	In the event we breach our payment obligations under the credit facility, or our obligations under any future third-party indebtedness, or if we become subject to certain bankruptcy, insolvency, liquidation or similar proceedings, in each case after any applicable cure periods, Dominion may accelerate our payment obligations and terminate the credit facility.
	•	We are required to obtain Dominion’s consent prior to creating any mortgage, security interest, lien or other encumbrance outside the ordinary course of business on any of our property, assets or revenues during the term of the facility. Failure to obtain any such consent from Dominion in the future could have an adverse impact on our ability to implement our business strategies, generate revenues and pay distributions to our unitholders.
	Subsidiary Debt Transactions
	At December 31, 2013, Cove Point was no longer a participant in the Dominion money pool. Interest charges related to Cove Point's borrowings from Dominion were $0.7 million and $1.4 million for the years ended December 31, 2013 and 2012, respectively. In 2013 and 2012, Cove Point capitalized interest costs and AFUDC to property, plant and equipment of $0.7 million and $1.3 million, respectively. During 2013, outstanding current borrowings of $360.0 million were converted to an equity contribution.
	Income Taxes
	Prior to the Offering, Cove Point participated in Dominion's intercompany tax sharing agreement as described in Note 15. Cove Point's participation in this tax sharing agreement was terminated in 2014 in connection with the Offering. The balances for income taxes payable to Dominion are provided below:
	Year Ended December 31,	2013
	(millions)
	Current (recorded in accrued payroll and taxes)	$	1.5
	Noncurrent (recorded in other liabilities)	0.3
	At the time of the Offering of Dominion Midstream, Cove Point settled net income taxes payable and deferred income taxes to Dominion of $147.9 million through equity contributions from Dominion. Prior to the Offering, Cove Point settled net income taxes payable to Dominion of $1.2 million and $3.2 million through equity contributions from Dominion during the years ended December 31, 2014 and 2013, respectively.
	Natural Gas Imbalances
	Cove Point maintains natural gas imbalances with affiliates. The imbalances with affiliates are provided below:
	Year Ended December 31,	2014		2013
	(millions)
	Imbalances payable to affiliates	$	2.5	$	8.6
	Right of First Offer
	In connection with the Offering, we entered into a right of first offer agreement with Dominion, pursuant to which Dominion agreed and caused its affiliates to agree, for so long as Dominion or its affiliates, individually or as part of a group, control our general partner, that if Dominion or any of its affiliates decide to attempt to sell (other than to another affiliate of Dominion) the ROFO Assets, Dominion or its affiliate will notify us of its desire to sell such ROFO Assets and, prior to selling such ROFO Assets to a third-party, will negotiate with us exclusively and in good faith for a period of 30 days in order to give us an opportunity to enter into definitive documentation for the purchase and sale of such ROFO Assets on terms that are mutually acceptable to Dominion or its affiliate and us. If we and Dominion or its affiliate have not entered into a letter of intent or a definitive purchase and sale agreement with respect to such ROFO Assets within such 30-day period, or if any such letter of intent or agreement is entered into but subsequently terminated, Dominion or its affiliate may, at any time during the succeeding 150 day period, enter into a definitive transfer agreement with any third party with respect to such ROFO Assets on terms and conditions that, when taken as a whole, are superior, in the good faith determination of Dominion or its affiliate, to those set forth in the last written offer we had proposed during negotiations with Dominion or its affiliate, and Dominion or its affiliate has the right to sell such ROFO Assets pursuant to such transfer agreement.

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2014
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. Upon the closing of the Offering, Cove Point is now treated as a limited partnership, a pass-through entity for U.S. federal and state income tax purposes. Accordingly, Dominion Midstream’s Consolidated Financial Statements do not include income taxes for the period subsequent to the Offering.
	Prior to the completion of the Offering, Cove Point was not treated as a partnership for U.S. federal and state income tax purposes. Its business activities were included in the consolidated U.S. federal and certain state income tax returns of Dominion or DCPI. Cove Point’s current income taxes were based on taxable income or loss, determined on a separate company basis, and, where applicable, settled in accordance with the principles of Dominion’s intercompany tax sharing agreement.
	The income tax (benefit) provision is summarized as follows:
	Year Ended December 31,	2014(1)			2013			2012
	(millions)
	Current:
	Federal	$	33.6		$	47.4		$	35.5
	State	5.1			7			8.3
	Total current expense	38.7			54.4			43.8
	Deferred:
	Federal	9.9			11.7			17
	State	3.2			(4.4		)	5.1
	Total deferred expense	13.1			7.3			22.1
	Total income tax expense	$	51.8		$	61.7		$	65.9
	-1	Income taxes recognized prior to the Offering.
	The statutory U.S. federal income tax rate reconciles to the effective income tax rate as follows:
	Year Ended December 31,	2014		2013		2012
	U.S. statutory rate	35	%	35	%	35	%
	Partnership income not subject to income taxes(1)	(5.8	)	—		—
	Increases resulting from:
	State taxes, net of federal benefit	3.4		1		5.3
	Other, net	0.1		0.1		0.1
	Effective tax rate	32.7	%	36.1	%	40.4	%
	-1	Reflects the pass-through entity status of Dominion Midstream and Cove Point subsequent to the Offering.
	The 2013 effective tax rate reflects a benefit resulting from a change in the allocation of Cove Point's income to states.
	Deferred income taxes consisted of the following:
	At December 31,	2014(1)			2013
	(millions)
	Deferred income taxes:
	Total deferred income tax assets	$	—		$	36
	Total deferred income tax liabilities	—			170.1
	Total net deferred income tax liabilities	$	—		$	134.1
	Total deferred income taxes:
	Plant and equipment, primarily depreciation method and basis differences	$	—		$	128.3
	Uncovered energy costs consumed in operations	—			2
	Deferred state income taxes	—			15.3
	Federal benefit of deferred state income taxes	—			(5.4		)
	Pension and other postretirement benefits	—			(1.4		)
	Other	—			(4.7		)
	Total net deferred income tax liabilities	$	—		$	134.1
	-1	Reflects the settlement of Cove Point's existing deferred taxes at the time of the Offering.
	Effective for its 2014 tax year, Dominion has been accepted into the CAP. The CAP is a method of identifying and resolving tax issues through open, cooperative, and transparent interaction between the IRS and taxpayers prior to the filing of a return. Through the CAP, Dominion will have the opportunity to resolve complex tax matters with the IRS before filing its federal income tax returns, thus achieving certainty for such tax return filing positions accepted by the IRS. Under a Pre-CAP plan, the IRS audit of tax years 2012 and 2013 began in early 2014.
	Unrecognized tax benefits were immaterial for 2014, 2013 and 2012.
	The earliest tax year remaining open for examination of Dominion's federal tax returns is 2012, and the only major state in which Cove Point operates is Maryland, for which the earliest tax year remaining open for examination is 2010. Dominion is obligated to report adjustments resulting from IRS settlements to state tax authorities.
	With the termination of Cove Point's participation in Dominion's intercompany tax sharing agreement, Dominion will pay the additional income taxes, if any, assessed by tax authorities related to Cove Point's business activities occurring prior to October 20, 2014.

Unit_Based_Compensation

Unit Based Compensation	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Unit Based Compensation	UNIT-BASED COMPENSATION
	In October 2014, the Board of Directors of our general partner adopted the Dominion Midstream LTIP. Awards under the Dominion Midstream LTIP are available for directors of our general partner and employees and consultants of our general partner and any of its affiliates, including Dominion, who perform services for us. The Dominion Midstream LTIP authorizes the grant, from time to time, at the discretion of the Board of Directors of our general partner or a committee thereof, of restricted units, phantom units, unit options, unit appreciation rights, distribution equivalent rights, other unit-based awards, substitute awards, unrestricted unit awards and cash awards. No more than 3,000,000 of our common units will be available for delivery under the Dominion Midstream LTIP. The common units to be delivered under the Dominion Midstream LTIP will consist, in whole or in part, of common units acquired in the open market or from any affiliate or any other person, newly issued common units or any combination of the foregoing as determined by the Board of Directors of our general partner or a committee thereof.
	In October 2014, 2,322 common units were issued to the non-employee directors of the general partner of Dominion Midstream as part of the prorated annual retainer and $0.1 million of expense was recognized within other operations and maintenance in the Consolidated Statement of Income. In January 2015, 5,055 common units were issued to the non-employee directors of the general partner of Dominion Midstream as an equity retainer granted under the Dominion Midstream LTIP.

Operating_Segment

Operating Segment	12 Months Ended
	Dec. 31, 2014
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 natural gas transportation, storage and regasification services.
	Dominion Midstream also reports a Corporate and Other segment. The Corporate and Other segment primarily includes specific 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. In 2013, there was a net charge of $0.1 million related to severance. There were no such items in 2014.
	The following table presents segment information pertaining to Dominion Midstream's operations:
	Year Ended December 31,	Dominion Energy		Corporate and			Consolidated Total
				Other
	(millions)
	2014
	Operating revenue	$	313.3	$	—		$	313.3
	Depreciation and amortization	37.7		—			37.7
	Interest and related charges	—		—			—
	Income tax expense	51.8		—			51.8
	Net income including noncontrolling interest	106.9		—			106.9
	Net income including noncontrolling interest subsequent to initial public offering	26.3		—			26.3
	Net income attributable to limited partners subsequent to initial public offering	9.5		—			9.5
	Capital expenditures	572.2		—			572.2
	Total assets at December 31	2,258.40		—			2,258.40
	2013
	Operating revenue	$	343.5	$	—		$	343.5
	Depreciation and amortization	31.7		—			31.7
	Interest and related charges	—		—			—
	Income tax expense	61.7		—			61.7
	Net income including noncontrolling interest	109.5		(0.1		)	109.4
	Capital expenditures	294.6		—			294.6
	Total assets at December 31	1,498.20		—			1,498.20
	2012
	Operating revenue	$	293	$	—		$	293
	Depreciation and amortization	33.3		—			33.3
	Interest and related charges	0.1		—			0.1
	Income tax expense	65.9		—			65.9
	Net income including noncontrolling interest	97.2		—			97.2
	Capital expenditures	51.1		—			51.1

Quarterly_Financial_and_Per_Un

Quarterly Financial and Per Unit Data (Unaudited)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial and Per Unit Data	QUARTERLY FINANCIAL AND PER UNIT DATA (UNAUDITED)
	A summary of Dominion Midstream's quarterly results of operations for the years ended December 31, 2014 and 2013 follows. The information includes the results of operations of our Predecessor prior to October 20, 2014 and of Dominion Midstream for the period beginning October 20, 2014, the date the Offering was completed, through December 31, 2014. Net income per unit is only calculated after the Offering, as no units were outstanding prior to October 20, 2014. Amounts reflect all adjustments necessary in the opinion of management for a fair statement of the results for the interim periods.
		First Quarter		Second Quarter		Third Quarter		Fourth Quarter		Full Year
	(millions, except per unit data)
	2014
	Operating revenue	$	68.9	$	111.2	$	65.7	$	67.5	$	313.3
	Income from operations	39.8		39.2		42.8		36.9		158.7
	Net income including noncontrolling interest	24.6		24.2		26.4		31.7		106.9
	Net income including noncontrolling interest subsequent to initial public offering							26.3		26.3
	Net income attributable to limited partners subsequent to initial public offering							9.5		9.5
	Net income subsequent to initial public offering per unit (basic and diluted)
	Common Units							$	0.15	$	0.15
	Subordinated Units							0.15		0.15
	Distributions declared per unit							0.1389		0.1389
	2013
	Operating revenue	$	104.7	$	67.1	$	104.2	$	67.5	$	343.5
	Income from operations	41.1		43.1		43		43.9		171.1
	Net income	24.5		31.1		26.5		27.3		$	109.4
	-1	On January 23, 2015, the Board of Directors of our general partner declared a prorated initial quarterly cash distribution of $0.1389 per unit, totaling $8.9 million, for the period subsequent to the Offering. This distribution was paid on February 13, 2015 to unitholders of record on February 3, 2015. The initial quarterly cash distribution was calculated as the minimum quarterly distribution of $0.1750 per unit prorated for the portion of the quarter subsequent to the Offering.

Significant_Accounting_Policie1

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2014
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. Dominion Midstream owns the general partner interest and controls Cove Point 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.
	For the periods prior to the closing of the Offering on October 20, 2014, the financial statements included in this Annual Report on Form 10-K were derived from the financial statements and accounting records of Cove Point as our predecessor. The financial statements were prepared using Dominion's historical basis in the assets and liabilities of Cove Point and include all revenues, costs, assets and liabilities attributed to Cove Point.
	For the period subsequent to the closing of the Offering, the Consolidated Financial Statements represent the consolidated results of operations, financial position and cash flows of Dominion Midstream.
	•	The consolidated statements of income and cash flows for the year ended December 31, 2014, consist of the consolidated results of Dominion Midstream for the period from October 20, 2014 through December 31, 2014, and the results of our Predecessor for the period from January 1, 2014, through October 19, 2014.
	•	The consolidated balance sheet at December 31, 2014, consists of the consolidated balances of Dominion Midstream.
	•	The consolidated statement of equity and partners' capital for the year ended December 31, 2014, consists of both the activity for our Predecessor prior to October 20, 2014, and the consolidated activity for Dominion Midstream completed at and subsequent to the Offering on October 20, 2014.
	The financial statements for all years presented include costs for certain general, administrative and corporate expenses assigned by DRS to Dominion Midstream and Cove Point on the basis of direct and allocated methods in accordance with Dominion Midstream and Cove Point's services agreements with DRS. Where costs incurred cannot be determined by specific identification, the costs are allocated based on the proportional level of effort devoted by DRS resources that is attributable to the entities, determined by reference to number of employees, salaries and wages and other similar measures for the relevant DRS department. Management believes the assumptions and methodologies underlying the allocation of general corporate overhead expenses are reasonable. Nevertheless, the Consolidated Financial Statements prior to the Offering may not include all of the actual expenses that would have been incurred had we been a stand-alone publicly traded partnership during the periods presented, and may not reflect our actual results of operations, financial position and cash flows had we been a stand-alone publicly traded partnership during the periods prior to the Offering.
Segment Reporting	Dominion Midstream reports one operating segment, Dominion Energy, which consists of LNG import, transportation and storage. In addition to the Dominion Energy operating segment, Dominion Midstream also reports a Corporate and Other segment, which primarily includes specific items attributable to its operating segment that are not included in profit measures evaluated by executive management in assessing the segment's performance. See Note 17 for further discussions of Dominion Midstream's operating segment.
Estimates	Dominion Midstream makes certain estimates and assumptions in preparing its 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, expenses, and cash flows for the periods presented. Actual results may differ from those estimates.
Operating Revenue	Operating Revenue
	Operating revenue is recorded on the basis of services rendered, commodities delivered or contracts settled and includes amounts yet to be billed to customers. Cove Point is currently generating significant revenue and earnings from annual reservation payments under long-term regasification, firm peaking storage and firm transportation contracts. Customer receivables at December 31, 2014 and 2013 included $19.9 million and $20.0 million, respectively, of accrued unbilled revenue based on estimated amounts of natural gas delivered but not yet billed to its customers.
	Cove Point renegotiated certain import-related contracts which will result in annual payments in the years 2013 through 2017 totaling approximately $50 million. Deferred revenue represents the difference between the amount received and the revenue recognized.
	The primary types of sales and service activities reported as operating revenue are as follows:
	•	Gas transportation and storage revenue consists primarily of storage services and transmission services; and
	•	Other revenue consists primarily of sales of purchased gas retained for use in routine operations and LNG cargos and the renegotiated contract payments described above.
Purchased Gas - Deferred Costs	Purchased Gas - Deferred Costs
	The difference between purchased gas expenses and the related levels of recovery for these expenses in current rates are deferred and matched against recoveries in future periods. The deferral of costs in excess of current period fuel rate recovery is recognized as a regulatory asset, while rate recovery in excess of current period fuel expenses is recognized as a regulatory liability.
Income Taxes	Income Taxes
	Dominion Midstream is organized as an MLP. As a pass-through entity for U.S. federal and state income tax purposes, each of its unitholders 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. Income before taxes, as determined under GAAP, may differ significantly from taxable income reportable to unitholders. Such differences may result from different bases of assets and liabilities and timing of recognition for income, gains, losses and expenditures for tax and financial reporting purposes, as well as the taxable income allocation requirements under the partnership agreement.
	As an MLP, at least 90% of Dominion Midstream’s total gross income must constitute qualifying income, determined on a calendar year basis under applicable income tax law. If the amount of qualifying income does not satisfy this requirement, Dominion Midstream would be taxed as a corporation. For the period October 20, 2014, through December 31, 2014, Dominion Midstream’s qualifying income exceeded the required amount. The Consolidated Financial Statements reflect management’s conclusion that Dominion Midstream’s status as a pass-through entity, if examined, would be sustained based on the technical merits of applicable tax law.
	Prior to the Offering, Cove Point was not a separate taxable entity for U.S. federal and state income tax purposes. Cove Point’s business activities were included in the consolidated U.S. federal income tax return filed by Dominion and its subsidiaries, DCPI’s Maryland state income tax returns and combined Virginia income tax returns filed by Dominion and certain subsidiaries. With Dominion Midstream’s acquisition of the Preferred Equity Interest and the general partnership interest in Cove Point, Cove Point is now treated as a limited partnership, a pass-through entity for U.S. federal and state income tax purposes. Dominion Midstream’s Consolidated Financial Statements reflect Cove Point’s income taxes for the period prior to the Offering.
	Cove Point’s current income taxes were based on taxable income or loss, determined on a separate company basis, and, where applicable, settled in accordance with the principles of Dominion’s intercompany tax sharing agreement. Deferred income tax assets and liabilities were provided, representing future effects on income taxes for temporary differences between the bases of assets and liabilities for financial reporting and tax purposes. Accordingly, deferred taxes were recognized for the future consequences of different treatments used for the reporting of transactions in financial accounting and income tax returns. In addition, a valuation allowance was established when it was more-likely-than-not that all, or a portion, of a deferred tax asset would not be realized. Where the treatment of temporary differences was different for rate-regulated operations, a regulatory asset was recognized if it is probable that future revenues would be provided for the payment of deferred tax liabilities. Reported amounts of assets and liabilities exceeded tax bases by $386.4 million at December 31, 2014.
	Judgment and the use of estimates are required in developing the provision for income taxes and reporting of tax-related assets and liabilities. The interpretation of tax laws involves uncertainty, since tax authorities may interpret the laws differently. For periods in which income taxes are included, a position taken, or expected to be taken, in income tax returns is recognized only if it is more-likely-than-not to be realized, assuming that the position will be examined by tax authorities with full knowledge of all relevant information. If it is not more-likely-than-not that a tax position, or some portion thereof, will be sustained, the related tax benefits are not recognized in the financial statements. Unrecognized tax benefits may result in an increase in income taxes payable, a reduction of income tax refunds receivable or changes in deferred taxes. Also, when uncertainty about the deductibility of an amount is limited to the timing of such deductibility, the increase in income taxes payable (or reduction in tax refunds receivable) is accompanied by a decrease in deferred tax liabilities. Except when such amounts are presented net with amounts receivable from or amounts prepaid to tax authorities, noncurrent income taxes payable related to unrecognized tax benefits are classified in other deferred credits and other liabilities and current payables are included in accrued interest, payroll and taxes on the Consolidated Balance Sheets.
	Under Dominion’s tax sharing agreement, payments of federal and state income taxes of $38.6 million, $52.6 million and $42.1 million were made to Dominion and DCPI for the years ended December 31, 2014, 2013 and 2012, respectively. The settlement of Cove Point’s obligations related to existing federal and state net income tax payables and deferred income taxes at the time of the Offering is reflected as an equity contribution in Dominion Midstream’s Consolidated Financial Statements.
	Interest accrued on uncertain tax positions is included in interest expense or income, as applicable. No penalties were accrued and interest expense was not material in all years presented.
Cash and Cash Equivalents	Cash and Cash Equivalents
	Current banking arrangements generally do not require checks to be funded until they are presented for payment. At December 31, 2014 and 2013, accounts payable included $0.4 million and $0.2 million, respectively, of checks outstanding but not yet presented for payment. For purposes of the Balance Sheets and Statements of Cash Flows, cash and cash equivalents include cash on hand, cash in banks and temporary investments purchased with an original maturity of three months or less.
Property, Plant and Equipment	Property, Plant and Equipment
	Property, plant and equipment, including additions and replacements is recorded at original cost, consisting of labor and materials and other costs such as asset retirement costs, capitalized interest and, for certain operations subject to cost-of-service rate regulation, AFUDC and overhead costs. The cost of repairs and maintenance, including minor additions and replacements, is charged to expense as it is incurred.
	In 2014, Dominion Midstream capitalized AFUDC of $0.1 million to property, plant and equipment. In 2013 and 2012, Dominion Midstream capitalized interest costs and AFUDC of $0.7 million and $1.3 million, respectively, to property, plant and equipment.
	For property subject to cost-of-service rate regulation, the undepreciated cost of such property, less salvage value, is generally charged to accumulated depreciation at retirement. Cost of removal collections not representing AROs are recorded as regulatory liabilities.
	For property that is not subject to cost-of-service rate regulation, cost of removal not associated with AROs is charged to expense as incurred. Dominion Midstream also records gains and losses upon retirement based upon the difference between the proceeds received, if any, and the property’s net book value at the retirement date.
	Depreciation of property, plant and equipment is computed on the straight-line method based on projected service lives. Depreciation rates on utility property, plant and equipment are as follows:
	Year Ended December 31,	2014	2013	2012
	(percent)
	Storage	2.39	2.43	2.6
	Transmission	2.81	2.83	2.83
	General and other	4.09	3.71	5.35
	In 2014, Cove Point shortened the useful life of assets expected to be retired as a result of commencement of construction on the generating station associated with the Liquefaction Project, which resulted in an increase to depreciation expense of $6.2 million. In 2013, Cove Point extended the useful life of existing expansion assets by nine years as a result of the Liquefaction Project, which resulted in a decrease to depreciation expense of $1.5 million ($1.0 million after tax).
Long-Lived and Intangible Assets	Long-Lived and Intangible Assets
	Dominion Midstream performs an evaluation for impairment whenever events or changes in circumstances indicate that the carrying amount of long-lived assets or intangible assets with finite lives may not be recoverable. A long-lived or intangible asset is written down to fair value if the sum of its expected future undiscounted cash flows is less than its carrying amount. Intangible assets with finite lives are amortized over their estimated useful lives.
Regulatory Assets and Liabilities	Regulatory Assets and Liabilities
	For regulated businesses subject to FERC cost-of-service rate regulation, regulatory practices that assign costs to accounting periods may differ from accounting methods generally applied by nonregulated companies. When it is probable that the FERC will permit the recovery of current costs through future rates charged to customers, these costs that otherwise would be expensed by nonregulated companies are deferred as regulatory assets. Likewise, regulatory liabilities are recognized when it is probable that the FERC will require customer refunds through future rates or when revenue is collected from customers for expenditures that have yet to be incurred. Generally, regulatory assets and liabilities are amortized into income over the period authorized by the FERC.
	Dominion Midstream evaluates whether or not recovery of its regulatory assets through future rates is probable and makes various assumptions in its analyses. The expectations of future recovery are generally based on orders issued by the FERC or historical experience, as well as discussions with the FERC. If recovery of a regulatory asset is determined to be less than probable, it will be written off in the period such assessment is made.
Materials and Supplies	Materials and Supplies
	Materials and supplies are valued primarily using the weighted-average cost method.
Natural Gas Imbalances	Natural Gas Imbalances
	Natural gas imbalances occur when the physical amount of natural gas delivered from, or received by, a pipeline system or storage facility differs from the contractual amount of natural gas delivered or received. Dominion Midstream values these imbalances due to, or from, shippers and operators at an appropriate index price at period end, subject to the terms of its tariff for regulated entities. Imbalances are primarily settled in-kind. Imbalances due to Dominion Midstream from other parties are reported as current assets and imbalances that Dominion Midstream owes to other parties are reported as current liabilities in the Consolidated Balance Sheets.
Goodwill	Goodwill
	Dominion Midstream evaluates goodwill for impairment annually as of April 1 and whenever an event occurs or circumstances change in the interim that would more-likely-than-not reduce the fair value of its reporting unit below its carrying value.

Initial_Public_Offering_Tables

Initial Public Offering (Tables)	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Schedule of Cash Proceeds
	Reconciliation of Cash Proceeds
	(millions)
	Total proceeds from the Offering	$	422.6
	Less: Underwriting discounts, structuring fees and offering expenses	(30.2		)
	Net proceeds from the Offering	392.4
	Less: Contribution to Cove Point for remaining portion of Preferred Equity Interest	340.9
	Net proceeds distributed to Dominion from the Offering	$	51.5

Significant_Accounting_Policie2

Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Schedule of Depreciation rates on Utility Property, Plant and Equipment	Depreciation rates on utility property, plant and equipment are as follows:
	Year Ended December 31,	2014	2013	2012
	(percent)
	Storage	2.39	2.43	2.6
	Transmission	2.81	2.83	2.83
	General and other	4.09	3.71	5.35
	Major classes of property, plant and equipment and their respective balances for Dominion Midstream are as follows:
	At December 31,	2014			2013
	(millions)
	Storage	$	882		$	869.1
	Transmission	323.9			319.3
	Plant under construction	972.3			352.7
	General and other	24.9			24.6
	Total property, plant and equipment	$	2,203.10		$	1,565.70

Net_Income_Per_Unit_Tables

Net Income Per Unit (Tables)	12 Months Ended
	Dec. 31, 2014
Earnings Per Share [Abstract]
Schedule of Calculation of Earnings per Unit	The calculation of earnings per unit is as follows:
	Year Ended December 31,	2014
	(millions)
	Net income attributable to limited partners subsequent to initial public offering	$	9.5
	Less distributions declared on(1):
	Incentive distribution holder rights(2)	—
	Common unitholders(3)	4.5
	Subordinated unitholder(3)	4.4
	Total distributions declared	8.9
	Undistributed earnings	$	0.6
	-1	On January 23, 2015, the Board of Directors of our general partner declared a prorated initial quarterly cash distribution of $0.1389 per unit, totaling $8.9 million, for the period subsequent to the Offering. This distribution was paid on February 13, 2015 to unitholders of record on February 3, 2015. The initial quarterly cash distribution was calculated as the minimum quarterly distribution of $0.1750 per unit prorated for the portion of the quarter subsequent to the Offering.
	-2	Dominion is a non-economic general partner that holds all of the IDRs.
	-3	Allocation of distributions declared has been adjusted for rounding.
	Basic and diluted net income subsequent to initial public offering per unit
		Common Units		Subordinated Units		Total
	(millions, except for weighted average units and per unit data)
	Distributions declared(1)	$	4.5	$	4.4	$	8.9
	Undistributed earnings	0.3		0.3		0.6
	Net income attributable to limited partners subsequent to initial public offering	$	4.8	$	4.7	$	9.5
	Weighted average units outstanding	31,975,079		31,972,789		63,947,868
	Net income per unit	$	0.15	$	0.15	$	0.15
	-1	Allocation of distributions declared has been adjusted for rounding.

Operating_Revenue_Tables

Operating Revenue (Tables)	12 Months Ended
	Dec. 31, 2014
Revenue Recognition [Abstract]
Operating Revenue	Operating revenue consists of the following:
	Year Ended December 31,	2014		2013		2012
	(millions)
	Gas transportation and storage	$	257.2	$	256.5	$	255.8
	Other	56.1		87		37.2
	Total operating revenue	$	313.3	$	343.5	$	293

Property_Plant_and_Equipment_T

Property Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Depreciation rates on utility property, plant and equipment are as follows:
	Year Ended December 31,	2014	2013	2012
	(percent)
	Storage	2.39	2.43	2.6
	Transmission	2.81	2.83	2.83
	General and other	4.09	3.71	5.35
	Major classes of property, plant and equipment and their respective balances for Dominion Midstream are as follows:
	At December 31,	2014			2013
	(millions)
	Storage	$	882		$	869.1
	Transmission	323.9			319.3
	Plant under construction	972.3			352.7
	General and other	24.9			24.6
	Total property, plant and equipment	$	2,203.10		$	1,565.70

Goodwill_and_Intangible_Assets1

Goodwill and Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	There have been no changes in Dominion Midstream's carrying amount and segment allocation of goodwill as presented below:
		Dominion Energy		Corporate and Other		Total
	(millions)
	Balance at December 31, 2012(1)	$	45.9	$	—	$	45.9
	No events affecting goodwill	—		—		—
	Balance at December 31, 2013(1)	$	45.9	$	—	$	45.9
	No events affecting goodwill	—		—		—
	Balance at December 31, 2014(1)	$	45.9	$	—	$	45.9
	-1	There are no accumulated impairment losses.
Schedule of Finite-Lived Intangible Assets	The components of intangible assets are as follows:
	At December 31,	2014				2013
		Gross		Accumulated		Gross		Accumulated
		Carrying		Amortization		Carrying		Amortization
		Amount				Amount
	(millions)
	Software and other	$	6.5	$	2.4	$	6.5	$	2.1
	Licenses	11		3		11		2.9
	Total	$	17.5	$	5.4	$	17.5	$	5
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense	Annual amortization expense for these intangible assets is estimated to be as follows:
		2015		2016		2017		2018		2019
	(millions)
		$	0.5	$	0.5	$	0.5	$	0.5	$	0.5

Regulatory_Assets_and_Liabilit1

Regulatory Assets and Liabilities (Tables)	12 Months Ended
	Dec. 31, 2014
Regulated Operations [Abstract]
Schedule of Regulatory Assets	Regulatory assets and liabilities include the following:
	At December 31,	2014		2013
	(millions)
	Regulatory assets:
	Unrecovered gas costs(1)	$	1.5	$	5.4
	Other	0.2		0.1
	Regulatory assets-current	1.7		5.5
	Income taxes recoverable through future rates(2)	2.5		2.5
	Regulatory assets-non-current	2.5		2.5
	Total regulatory assets	$	4.2	$	8
	Regulatory liabilities:
	Overrecovered gas costs(1)	$	0.5	$	0.8
	LNG cargo obligations(3)	3		6.7
	Other	0.1		0.2
	Regulatory liabilities-current	3.6		7.7
	Provision for future cost of removal(4)	33		29.5
	Other	0.5		0.9
	Regulatory liabilities-non-current	33.5		30.4
	Total regulatory liabilities	$	37.1	$	38.1
	-1	Reflects unrecovered/overrecovered gas costs at Cove Point, which are subject to annual filings with the FERC.
	-2	Amounts to be recovered through future rates to provide for income taxes that become payable by unitholders when rate revenue is provided to recover AFUDC-equity when such amounts are recovered through book depreciation.
	-3	Represents obligations to the Import Shippers for LNG cargo received. See Note 9 for further information.
	-4	Rates charged to customers by Cove Point include a provision for the cost of future activities to remove assets that are expected to be incurred at the time of retirement.
Schedule of Regulatory Liabilities	Regulatory assets and liabilities include the following:
	At December 31,	2014		2013
	(millions)
	Regulatory assets:
	Unrecovered gas costs(1)	$	1.5	$	5.4
	Other	0.2		0.1
	Regulatory assets-current	1.7		5.5
	Income taxes recoverable through future rates(2)	2.5		2.5
	Regulatory assets-non-current	2.5		2.5
	Total regulatory assets	$	4.2	$	8
	Regulatory liabilities:
	Overrecovered gas costs(1)	$	0.5	$	0.8
	LNG cargo obligations(3)	3		6.7
	Other	0.1		0.2
	Regulatory liabilities-current	3.6		7.7
	Provision for future cost of removal(4)	33		29.5
	Other	0.5		0.9
	Regulatory liabilities-non-current	33.5		30.4
	Total regulatory liabilities	$	37.1	$	38.1
	-1	Reflects unrecovered/overrecovered gas costs at Cove Point, which are subject to annual filings with the FERC.
	-2	Amounts to be recovered through future rates to provide for income taxes that become payable by unitholders when rate revenue is provided to recover AFUDC-equity when such amounts are recovered through book depreciation.
	-3	Represents obligations to the Import Shippers for LNG cargo received. See Note 9 for further information.
	-4	Rates charged to customers by Cove Point include a provision for the cost of future activities to remove assets that are expected to be incurred at the time of retirement.

Related_Party_Transactions_Tab

Related Party Transactions (Tables)	12 Months Ended
	Dec. 31, 2014
Related Party Transactions [Abstract]
Schedule of Related Party Transactions	The affiliated transactions are presented below:
	Year Ended December 31,	2014		2013		2012
	(millions)
	Sales of natural gas transportation services to affiliates	$	2.4	$	2.3	$	2.1
	Purchased gas from affiliates	0.6		0.7		—
	Services provided by DRS(1)(2)	12.3		9.3		6.1
	Goods and services provided by affiliates to Cove Point(1)	3.8		3.2		3
	-1	Includes $6.7 million, $4.8 million and $2.1 million of capitalized expenditures in 2014, 2013 and 2012, respectively.
	-2	Dominion Midstream determined that neither it nor Cove Point is the most closely associated entity with DRS, an affiliated variable interest entity, and therefore neither is the primary beneficiary. DRS provides accounting, legal, finance and certain administrative and technical services to all Dominion subsidiaries, including Dominion Midstream and Cove Point. Neither Dominion Midstream nor Cove Point has an obligation to absorb more than its allocated share of DRS costs.
	The imbalances with affiliates are provided below:
	Year Ended December 31,	2014		2013
	(millions)
	Imbalances payable to affiliates	$	2.5	$	8.6
	The balances for income taxes payable to Dominion are provided below:
	Year Ended December 31,	2013
	(millions)
	Current (recorded in accrued payroll and taxes)	$	1.5
	Noncurrent (recorded in other liabilities)	0.3

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit)	The income tax (benefit) provision is summarized as follows:
	Year Ended December 31,	2014(1)			2013			2012
	(millions)
	Current:
	Federal	$	33.6		$	47.4		$	35.5
	State	5.1			7			8.3
	Total current expense	38.7			54.4			43.8
	Deferred:
	Federal	9.9			11.7			17
	State	3.2			(4.4		)	5.1
	Total deferred expense	13.1			7.3			22.1
	Total income tax expense	$	51.8		$	61.7		$	65.9
	-1	Income taxes recognized prior to the Offering.
Schedule of Effective Income Tax Rate Reconciliation	The statutory U.S. federal income tax rate reconciles to the effective income tax rate as follows:
	Year Ended December 31,	2014		2013		2012
	U.S. statutory rate	35	%	35	%	35	%
	Partnership income not subject to income taxes(1)	(5.8	)	—		—
	Increases resulting from:
	State taxes, net of federal benefit	3.4		1		5.3
	Other, net	0.1		0.1		0.1
	Effective tax rate	32.7	%	36.1	%	40.4	%
	-1	Reflects the pass-through entity status of Dominion Midstream and Cove Point subsequent to the Offering.
Schedule of Deferred Tax Assets and Liabilities	Deferred income taxes consisted of the following:
	At December 31,	2014(1)			2013
	(millions)
	Deferred income taxes:
	Total deferred income tax assets	$	—		$	36
	Total deferred income tax liabilities	—			170.1
	Total net deferred income tax liabilities	$	—		$	134.1
	Total deferred income taxes:
	Plant and equipment, primarily depreciation method and basis differences	$	—		$	128.3
	Uncovered energy costs consumed in operations	—			2
	Deferred state income taxes	—			15.3
	Federal benefit of deferred state income taxes	—			(5.4		)
	Pension and other postretirement benefits	—			(1.4		)
	Other	—			(4.7		)
	Total net deferred income tax liabilities	$	—		$	134.1
	-1	Reflects the settlement of Cove Point's existing deferred taxes at the time of the Offering.

Operating_Segment_Tables

Operating Segment (Tables)	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment	The following table presents segment information pertaining to Dominion Midstream's operations:
	Year Ended December 31,	Dominion Energy		Corporate and			Consolidated Total
				Other
	(millions)
	2014
	Operating revenue	$	313.3	$	—		$	313.3
	Depreciation and amortization	37.7		—			37.7
	Interest and related charges	—		—			—
	Income tax expense	51.8		—			51.8
	Net income including noncontrolling interest	106.9		—			106.9
	Net income including noncontrolling interest subsequent to initial public offering	26.3		—			26.3
	Net income attributable to limited partners subsequent to initial public offering	9.5		—			9.5
	Capital expenditures	572.2		—			572.2
	Total assets at December 31	2,258.40		—			2,258.40
	2013
	Operating revenue	$	343.5	$	—		$	343.5
	Depreciation and amortization	31.7		—			31.7
	Interest and related charges	—		—			—
	Income tax expense	61.7		—			61.7
	Net income including noncontrolling interest	109.5		(0.1		)	109.4
	Capital expenditures	294.6		—			294.6
	Total assets at December 31	1,498.20		—			1,498.20
	2012
	Operating revenue	$	293	$	—		$	293
	Depreciation and amortization	33.3		—			33.3
	Interest and related charges	0.1		—			0.1
	Income tax expense	65.9		—			65.9
	Net income including noncontrolling interest	97.2		—			97.2
	Capital expenditures	51.1		—			51.1

Quarterly_Financial_and_Per_Un1

Quarterly Financial and Per Unit Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	A summary of Dominion Midstream's quarterly results of operations for the years ended December 31, 2014 and 2013 follows. The information includes the results of operations of our Predecessor prior to October 20, 2014 and of Dominion Midstream for the period beginning October 20, 2014, the date the Offering was completed, through December 31, 2014. Net income per unit is only calculated after the Offering, as no units were outstanding prior to October 20, 2014. Amounts reflect all adjustments necessary in the opinion of management for a fair statement of the results for the interim periods.
		First Quarter		Second Quarter		Third Quarter		Fourth Quarter		Full Year
	(millions, except per unit data)
	2014
	Operating revenue	$	68.9	$	111.2	$	65.7	$	67.5	$	313.3
	Income from operations	39.8		39.2		42.8		36.9		158.7
	Net income including noncontrolling interest	24.6		24.2		26.4		31.7		106.9
	Net income including noncontrolling interest subsequent to initial public offering							26.3		26.3
	Net income attributable to limited partners subsequent to initial public offering							9.5		9.5
	Net income subsequent to initial public offering per unit (basic and diluted)
	Common Units							$	0.15	$	0.15
	Subordinated Units							0.15		0.15
	Distributions declared per unit							0.1389		0.1389
	2013
	Operating revenue	$	104.7	$	67.1	$	104.2	$	67.5	$	343.5
	Income from operations	41.1		43.1		43		43.9		171.1
	Net income	24.5		31.1		26.5		27.3		$	109.4
	-1	On January 23, 2015, the Board of Directors of our general partner declared a prorated initial quarterly cash distribution of $0.1389 per unit, totaling $8.9 million, for the period subsequent to the Offering. This distribution was paid on February 13, 2015 to unitholders of record on February 3, 2015. The initial quarterly cash distribution was calculated as the minimum quarterly distribution of $0.1750 per unit prorated for the portion of the quarter subsequent to the Offering.

Description_of_Business_and_Ba1

Description of Business and Basis of Presentation (Details)	3 Months Ended	0 Months Ended
	Dec. 31, 2014	Oct. 20, 2014
	Segment
Subsidiary, Sale of Stock [Line Items]
Number of operating segments	1
Common Units | IPO
Subsidiary, Sale of Stock [Line Items]
Number of units issued		20,125,000
Common Units | Over-Allotment Option
Subsidiary, Sale of Stock [Line Items]
Number of units issued		2,625,000

Initial_Public_Offering_Narrat

Initial Public Offering (Narrative) (Details) (USD $)	0 Months Ended
In Millions, except Share data, unless otherwise specified	Oct. 20, 2014	Oct. 20, 2014
IPO
Subsidiary, Sale of Stock [Line Items]
Public price per common unit	$21	$21
Amount of cash distribution	($51.50)
Net proceeds received from sale of common units	392.4
Underwriting discounts, structuring fees and offering expenses	30.2
Contribution to Cove Point for remaining portion of Preferred Equity Interest	340.9
IPO | Dominion
Subsidiary, Sale of Stock [Line Items]
Aggregate limited partner interest (percentage)	68.50%
IPO | Dominion | Cash Distribution
Subsidiary, Sale of Stock [Line Items]
Amount of cash distribution	$51.50
IPO | Common Units
Subsidiary, Sale of Stock [Line Items]
Number of units issued	20,125,000
IPO | Common Units | Dominion
Subsidiary, Sale of Stock [Line Items]
Number of units issued	11,847,789
IPO | Subordinated Units | Dominion
Subsidiary, Sale of Stock [Line Items]
Number of units issued	31,972,789
Over-Allotment Option | Common Units
Subsidiary, Sale of Stock [Line Items]
Number of units issued	2,625,000

Initial_Public_Offering_Reconc

Initial Public Offering (Reconciliation of Cash Proceeds) (Details) (IPO, USD $)	0 Months Ended
In Millions, unless otherwise specified	Oct. 20, 2014
IPO
Subsidiary, Sale of Stock [Line Items]
Total proceeds from the Offering	$422.60
Less: Underwriting discounts, structuring fees and offering expenses	-30.2
Net proceeds from the Offering	392.4
Less: Contribution to Cove Point for remaining portion of Preferred Equity Interest	340.9
Net proceeds distributed to Dominion from the Offering	$51.50

Significant_Accounting_Policie3

Significant Accounting Policies (Narrative) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Related Party Transaction [Line Items]
Customer receivables	$19.90	$20
Annual payments for certain import-related contracts	50
Income taxes	38.6
Checks outstanding but not yet presented for payment	0.4	0.2
Capitalized AFUDC	0.1
Interest costs and AFUDC capitalized to property, plant and equipment		0.7	1.3
Tax Sharing Agreement | Affiliates
Related Party Transaction [Line Items]
Amount by which reported assets and liabilities exceeded tax bases	386.4
Income taxes	$38.60	$52.60	$42.10

Significant_Accounting_Policie4

Significant Accounting Policies (Schedule of Depreciation Rates on Public Utility Property Plant and Equipment) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Change in Estimated Useful Life
Property, Plant and Equipment [Line Items]
Change in depreciation expense due to change in estimated useful lives	6.2
Number of years useful life was extended		9 years
Decrease in depreciation expense		1.5
Decrease in depreciation expense, after tax		1
Storage
Property, Plant and Equipment [Line Items]
Depreciation rates (percentage)	2.39%	2.43%	2.60%
Transmission
Property, Plant and Equipment [Line Items]
Depreciation rates (percentage)	2.81%	2.83%	2.83%
General and other
Property, Plant and Equipment [Line Items]
Depreciation rates (percentage)	4.09%	3.71%	5.35%

Net_Income_Per_Unit_Details

Net Income Per Unit (Details) (USD $)	3 Months Ended		0 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2014		Jan. 23, 2015
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to limited partners subsequent to initial public offering	$9.50
Incentive distribution holder rights	0	[1],[2]
Total distributions declared	8.9	[3]
Undistributed earnings	0.6
Distributions declared per unit	$0.14
Weighted average units outstanding	63,947,868
Net income subsequent to initial public offering per unit (basic and diluted)	$0.15
Minimum
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Distributions declared per unit	$0.18
Subsequent Event
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Distribution declared on Common unitholders and Subordinated unitholder			8.9
Distributions declared per unit			$0.14
Common Units
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to limited partners subsequent to initial public offering	4.8	[4]
Distribution declared on Common unitholders and Subordinated unitholder	4.5	[1],[3]
Total distributions declared	4.5	[3]
Undistributed earnings	0.3
Weighted average units outstanding	31,975,079
Net income subsequent to initial public offering per unit (basic and diluted)	$0.15
Subordinated Units
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to limited partners subsequent to initial public offering	4.7	[4]
Distribution declared on Common unitholders and Subordinated unitholder	4.4	[1],[3]
Total distributions declared	4.4	[3]
Undistributed earnings	$0.30
Weighted average units outstanding	31,972,789
Net income subsequent to initial public offering per unit (basic and diluted)	$0.15
[1]	On January 23, 2015, the Board of Directors of our general partner declared a prorated initial quarterly cash distribution of $0.1389 per unit, totaling $8.9 million, for the period subsequent to the Offering. This distribution was paid on February 13, 2015 to unitholders of record on February 3, 2015. The initial quarterly cash distribution was calculated as the minimum quarterly distribution of $0.1750 per unit prorated for the portion of the quarter subsequent to the Offering.
[2]	Dominion is a non-economic general partner that holds all of the IDRs.
[3]	Allocation of distributions declared has been adjusted for rounding.
[4]	Allocation of net income attributable to partners' ownership interest subsequent to initial public offering has been adjusted for rounding.

Operating_Revenue_Details

Operating Revenue (Details) (USD $)

3 Months Ended

12 Months Ended

3 Months Ended

12 Months Ended

In Millions, unless otherwise specified

Dec. 31, 2014

Dec. 31, 2014

Sep. 30, 2014

Jun. 30, 2014

Mar. 31, 2014

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Public Utilities, General Disclosures [Line Items]

Gas transportation and storage

$257.20

Other

56.1

Total operating revenue

67.5

313.3

[1]

Predecessor

Public Utilities, General Disclosures [Line Items]

Gas transportation and storage

256.5

255.8

Other

87

37.2

Total operating revenue

$65.70

$111.20

$68.90

$67.50

$104.20

$67.10

$104.70

$343.50

[1]

$293

[1]

[1]

See Note 14 for amounts attributable to related parties.

Property_Plant_and_Equipment_D

Property Plant and Equipment (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$2,203.10
Storage
Property, Plant and Equipment [Line Items]
Property, plant and equipment	882
Transmission
Property, Plant and Equipment [Line Items]
Property, plant and equipment	323.9
Plant under construction
Property, Plant and Equipment [Line Items]
Property, plant and equipment	972.3
General and other
Property, Plant and Equipment [Line Items]
Property, plant and equipment	24.9
Predecessor
Property, Plant and Equipment [Line Items]
Property, plant and equipment		1,565.70
Predecessor | Storage
Property, Plant and Equipment [Line Items]
Property, plant and equipment		869.1
Predecessor | Transmission
Property, Plant and Equipment [Line Items]
Property, plant and equipment		319.3
Predecessor | Plant under construction
Property, Plant and Equipment [Line Items]
Property, plant and equipment		352.7
Predecessor | General and other
Property, Plant and Equipment [Line Items]
Property, plant and equipment		$24.60

Goodwill_and_Intangible_Assets2

Goodwill and Intangible Assets (Schedule of Goodwill) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2012		Dec. 31, 2013
Goodwill [Roll Forward]
No events affecting goodwill	$0
Balance	45.9	[1]
Dominion Energy
Goodwill [Roll Forward]
No events affecting goodwill	0
Balance	45.9	[1]
Corporate and Other
Goodwill [Roll Forward]
No events affecting goodwill	0
Balance	0	[1]
Predecessor
Goodwill [Roll Forward]
Balance					45.9	[1]
No events affecting goodwill			0
Balance			45.9	[1]	45.9	[1]
Predecessor | Dominion Energy
Goodwill [Roll Forward]
Balance					45.9	[1]
No events affecting goodwill			0
Balance			45.9	[1]	45.9	[1]
Predecessor | Corporate and Other
Goodwill [Roll Forward]
Balance					0	[1]
No events affecting goodwill			0
Balance			$0	[1]	$0	[1]
[1]	There are no accumulated impairment losses.

Goodwill_and_Intangible_Assets3

Goodwill and Intangible Assets (Narrative) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Finite-Lived Intangible Assets [Line Items]
Amortization expense for intangible assets	$0.60
Software and other
Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired	0.2
Weighted average amortization periods	5 years
Predecessor
Finite-Lived Intangible Assets [Line Items]
Amortization expense for intangible assets		0.6	0.7
Predecessor | Software and other
Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired		$0.20
Weighted average amortization periods		10 years

Goodwill_and_Intangible_Assets4

Goodwill and Intangible Assets (Schedule of Components of Intangible Assets) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$17.50
Accumulated Amortization	5.4
Software and other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	6.5
Accumulated Amortization	2.4
Licenses
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	11
Accumulated Amortization	3
Predecessor
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount		17.5
Accumulated Amortization		5
Predecessor | Software and other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount		6.5
Accumulated Amortization		2.1
Predecessor | Licenses
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount		11
Accumulated Amortization		$2.90

Goodwill_and_Intangible_Assets5

Goodwill and Intangible Assets (Schedule of Future Amortization Expense for Intangible Assets) (Details) (USD $)	Dec. 31, 2014
In Millions, unless otherwise specified
Goodwill and Intangible Assets Disclosure [Abstract]
2015	$0.50
2016	0.5
2017	0.5
2018	0.5
2019	$0.50

Regulatory_Assets_and_Liabilit2

Regulatory Assets and Liabilities (Regulatory Assets) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Regulatory Assets [Line Items]
Regulatory assets-current	$1.70
Regulatory assets-non-current	2.5
Total regulatory assets	4.2
Past expenditures in which no return is expected	1.7
Recovery period of expenditures	1 year
Unrecovered gas costs
Regulatory Assets [Line Items]
Regulatory assets-current	1.5	[1]
Other
Regulatory Assets [Line Items]
Regulatory assets-current	0.2
Income taxes recoverable through future rates
Regulatory Assets [Line Items]
Regulatory assets-non-current	2.5	[2]
Predecessor
Regulatory Assets [Line Items]
Regulatory assets-current			5.5
Regulatory assets-non-current			2.5
Total regulatory assets			8
Past expenditures in which no return is expected			5.5
Predecessor | Unrecovered gas costs
Regulatory Assets [Line Items]
Regulatory assets-current			5.4	[1]
Predecessor | Other
Regulatory Assets [Line Items]
Regulatory assets-current			0.1
Predecessor | Income taxes recoverable through future rates
Regulatory Assets [Line Items]
Regulatory assets-non-current			$2.50	[2]
[1]	Reflects unrecovered/overrecovered gas costs at Cove Point, which are subject to annual filings with the FERC.
[2]	Amounts to be recovered through future rates to provide for income taxes that become payable by unitholders when rate revenue is provided to recover AFUDC-equity when such amounts are recovered through book depreciation.

Regulatory_Assets_and_Liabilit3

Regulatory Assets and Liabilities (Regulatory Liabilities) (Details) (USD $)	Dec. 31, 2014		Dec. 31, 2013
In Millions, unless otherwise specified
Regulatory Liabilities [Line Items]
Regulatory liabilities-current	$3.60
Regulatory liabilities-non-current	33.5
Total regulatory liabilities	37.1
Overrecovered gas costs
Regulatory Liabilities [Line Items]
Regulatory liabilities-current	0.5	[1]
LNG cargo obligations
Regulatory Liabilities [Line Items]
Regulatory liabilities-current	3	[2]
Other
Regulatory Liabilities [Line Items]
Regulatory liabilities-current	0.1
Regulatory liabilities-non-current	0.5
Provision for future cost of removal
Regulatory Liabilities [Line Items]
Regulatory liabilities-non-current	33	[3]
Predecessor
Regulatory Liabilities [Line Items]
Regulatory liabilities-current			7.7
Regulatory liabilities-non-current			30.4
Total regulatory liabilities			38.1
Predecessor | Overrecovered gas costs
Regulatory Liabilities [Line Items]
Regulatory liabilities-current			0.8	[1]
Predecessor | LNG cargo obligations
Regulatory Liabilities [Line Items]
Regulatory liabilities-current			6.7	[2]
Predecessor | Other
Regulatory Liabilities [Line Items]
Regulatory liabilities-current			0.2
Regulatory liabilities-non-current			0.9
Predecessor | Provision for future cost of removal
Regulatory Liabilities [Line Items]
Regulatory liabilities-non-current			$29.50	[3]
[1]	Reflects unrecovered/overrecovered gas costs at Cove Point, which are subject to annual filings with the FERC.
[2]	Represents obligations to the Import Shippers for LNG cargo received. See Note 9 for further information.
[3]	Rates charged to customers by Cove Point include a provision for the cost of future activities to remove assets that are expected to be incurred at the time of retirement.

Employee_Benefit_Plans_Details

Employee Benefit Plans (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension and Other Postretirement Benefit Liabilities | Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amounts due to Dominion associated with benefit plans	$3.50
Pension and Other Postretirement Benefit Liabilities | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amounts due to Dominion associated with benefit plans	0.9
Other Operations And Maintenance Expense
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer matching contributions to plans	0.2
Other Operations And Maintenance Expense | Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic pension cost	1.1
Other Operations And Maintenance Expense | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic pension cost	-0.4
Predecessor | Pension and Other Postretirement Benefit Liabilities | Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amounts due to Dominion associated with benefit plans		2.5
Predecessor | Pension and Other Postretirement Benefit Liabilities | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amounts due to Dominion associated with benefit plans		1.6
Predecessor | Other Operations And Maintenance Expense
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer matching contributions to plans		0.2	0.2
Predecessor | Other Operations And Maintenance Expense | Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic pension cost		1.4	1.1
Predecessor | Other Operations And Maintenance Expense | Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic pension cost		$0.10	$0.20

CPCN_Obligation_Details

CPCN Obligation (Details) (USD $)	1 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014
Obligated Payments to Maryland Strategic Energy Investments Fund and Low Income Energy Assistance Programs
Other Commitments [Line Items]
Total amount of commitment	$48
Effective interest rate used to determine present value of obligation	1.90%
Obligated Payments to Maryland Strategic Energy Investments Fund
Other Commitments [Line Items]
Total amount of commitment	40
Period for required payments	5 years
Low Income Energy Assistance Programs
Other Commitments [Line Items]
Total amount of commitment	$8
Period for required payments	20 years

Commitments_and_Contingencies_

Commitments and Contingencies (Details) (USD $)	Dec. 31, 2014
Surety Bond
Other Commitments [Line Items]
Total amount of commitment	$10,800,000
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) (Customer Concentration Risk, Sales Revenue, Net)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
	customer	customer	customer
Concentration Risk [Line Items]
Number of customers	23
Marketers or End Users and Import Shippers
Concentration Risk [Line Items]
Number of customers	16
Three Largest Customers
Concentration Risk [Line Items]
Number of customers	3
Percentage of total transportation and storage revenues	93.00%
Largest Customer
Concentration Risk [Line Items]
Percentage of total transportation and storage revenues	72.00%
Predecessor | Three Largest Customers
Concentration Risk [Line Items]
Number of customers		3	3
Percentage of total transportation and storage revenues		94.00%	93.00%
Predecessor | Largest Customer
Concentration Risk [Line Items]
Percentage of total transportation and storage revenues		72.00%	72.00%

Related_Party_Transactions_Det

Related Party Transactions (Details) (USD $)	12 Months Ended						0 Months Ended	10 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012		Oct. 20, 2014	Oct. 19, 2014
Related Party Transaction [Line Items]
Capital expenditures	$572,200,000
Interest costs and AFUDC capitalized to property, plant and equipment			700,000		1,300,000
Imbalances payable to affiliates	2,700,000	[1]
Equity contribution from Dominion to relieve payables to affiliates
Related Party Transaction [Line Items]
Equity contribution from affiliate	20,000,000
Equity contribution from Dominion related to income taxes prior to the Offering
Related Party Transaction [Line Items]
Equity contribution from affiliate	1,200,000
Affiliates
Related Party Transaction [Line Items]
Sales of natural gas transportation services to affiliates	2,400,000
Capital expenditures	6,700,000
Imbalances payable to affiliates	2,500,000
Affiliates | Purchased gas from affiliates
Related Party Transaction [Line Items]
Purchased gas from affiliates	600,000
Affiliates | Services provided by DRS
Related Party Transaction [Line Items]
Amounts from transactions with related parties	12,300,000	[2],[3]
Affiliates | Goods and services provided by affiliates to Cove Point
Related Party Transaction [Line Items]
Amounts from transactions with related parties	3,800,000	[2]
General Partner Dominion (non-economic interest) | Credit Facility with Dominion | Credit Facility | IPO
Related Party Transaction [Line Items]
Borrowing capacity of credit facility							300,000,000
Amount of commitment fees							0
Ongoing facility or similar charges							0
Term of credit facility							5 years
General Partner Dominion (non-economic interest) | Tax Sharing Agreement | Equity contribution from Dominion related to income taxes prior to the Offering
Related Party Transaction [Line Items]
Equity contribution from affiliate							147,900,000
General Partner Dominion (non-economic interest) | Right of First Offer Agreement | IPO
Related Party Transaction [Line Items]
Period of ROFO Assets							30 days
General Partner Dominion (non-economic interest) | Right of First Offer Agreement | IPO | Maximum
Related Party Transaction [Line Items]
Period of ROFO Assets							150 days
Predecessor
Related Party Transaction [Line Items]
Capital expenditures			294,600,000		51,100,000
Imbalances payable to affiliates			9,400,000	[1]
Predecessor | Equity contribution from Dominion to relieve payables to affiliates
Related Party Transaction [Line Items]
Equity contribution from affiliate			100,900,000		0
Predecessor | Equity contribution from Dominion related to income taxes prior to the Offering
Related Party Transaction [Line Items]
Equity contribution from affiliate			3,200,000		3,400,000
Predecessor | Affiliates
Related Party Transaction [Line Items]
Sales of natural gas transportation services to affiliates			2,300,000		2,100,000
Capital expenditures			4,800,000		2,100,000
Imbalances payable to affiliates			8,600,000
Predecessor | Affiliates | Payables to Affiliates
Related Party Transaction [Line Items]
Advance from affiliate			20,000,000
Predecessor | Affiliates | Equity contribution from Dominion to relieve payables to affiliates
Related Party Transaction [Line Items]
Equity contribution from affiliate			100,900,000
Predecessor | Affiliates | Purchased gas from affiliates
Related Party Transaction [Line Items]
Purchased gas from affiliates			700,000		0
Predecessor | Affiliates | Services provided by DRS
Related Party Transaction [Line Items]
Amounts from transactions with related parties			9,300,000	[2],[3]	6,100,000	[2],[3]
Predecessor | Affiliates | Goods and services provided by affiliates to Cove Point
Related Party Transaction [Line Items]
Amounts from transactions with related parties			3,200,000	[2]	3,000,000	[2]
Predecessor | General Partner Dominion (non-economic interest)
Related Party Transaction [Line Items]
Interest charges related borrowings from Dominion			700,000		1,400,000
Interest costs and AFUDC capitalized to property, plant and equipment			700,000		1,300,000
Outstanding current borrowings converted to equity contribution			360,000,000
Predecessor | General Partner Dominion (non-economic interest) | Tax Sharing Agreement | Accrued Payroll and Taxes
Related Party Transaction [Line Items]
Current (recorded in accrued payroll and taxes)			1,500,000
Predecessor | General Partner Dominion (non-economic interest) | Tax Sharing Agreement | Other Liabilities
Related Party Transaction [Line Items]
Noncurrent (recorded in other liabilities)			300,000
Predecessor | General Partner Dominion (non-economic interest) | Tax Sharing Agreement | Equity contribution from Dominion related to income taxes prior to the Offering
Related Party Transaction [Line Items]
Equity contribution from affiliate			$3,200,000					$1,200,000
[1]	See Note 14 for amounts attributable to related parties.
[2]	Includes $6.7 million, $4.8 million and $2.1 million of capitalized expenditures in 2014, 2013 and 2012, respectively.
[3]	Dominion Midstream determined that neither it nor Cove Point is the most closely associated entity with DRS, an affiliated variable interest entity, and therefore neither is the primary beneficiary. DRS provides accounting, legal, finance and certain administrative and technical services to all Dominion subsidiaries, including Dominion Midstream and Cove Point. Neither Dominion Midstream nor Cove Point has an obligation to absorb more than its allocated share of DRS costs.

Income_Taxes_Schedule_of_Detai

Income Taxes (Schedule of Details of Income Tax Expense) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012
Current:
Federal	$33.60	[1]
State	5.1	[1]
Total current expense	38.7	[1]
Deferred:
Federal	9.9	[1]
State	3.2	[1]
Total deferred expense	13.1	[1]
Income tax expense	51.8	[1]
Predecessor
Current:
Federal			47.4	35.5
State			7	8.3
Total current expense			54.4	43.8
Deferred:
Federal			11.7	17
State			-4.4	5.1
Total deferred expense			7.3	22.1
Income tax expense			$61.70	$65.90
[1]	Income taxes recognized prior to the Offering.

Income_Taxes_Effective_Income_

Income Taxes (Effective Income Tax Rate Reconciliation) (Details)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Income Taxes [Line Items]
U.S. statutory rate	35.00%
Partnership income not subject to income taxes(1)	-5.80%	[1]
Increases resulting from:
State taxes, net of federal benefit	3.40%
Other, net	0.10%
Effective tax rate	32.70%
Predecessor
Income Taxes [Line Items]
U.S. statutory rate			35.00%		35.00%
Partnership income not subject to income taxes(1)			0.00%	[1]	0.00%	[1]
Increases resulting from:
State taxes, net of federal benefit			1.00%		5.30%
Other, net			0.10%		0.10%
Effective tax rate			36.10%		40.40%
[1]	Reflects the pass-through entity status of Dominion Midstream and Cove Point subsequent to the Offering.

Income_Taxes_Schedule_of_Defer

Income Taxes (Schedule of Deferred Income Taxes) (Details) (USD $)	Dec. 31, 2014		Dec. 31, 2013
In Millions, unless otherwise specified
Deferred income taxes:
Total deferred income tax assets	$0	[1]
Total deferred income tax liabilities	0	[1]
Total net deferred income tax liabilities	0	[1]
Total deferred income taxes:
Plant and equipment, primarily depreciation method and basis differences	0	[1]
Uncovered energy costs consumed in operations	0	[1]
Deferred state income taxes	0	[1]
Deferred state income taxes	0	[1]
Pension and other postretirement benefits	0	[1]
Other	0	[1]
Total net deferred income tax liabilities	0	[1]
Predecessor
Deferred income taxes:
Total deferred income tax assets			36
Total deferred income tax liabilities			170.1
Total net deferred income tax liabilities			134.1
Total deferred income taxes:
Plant and equipment, primarily depreciation method and basis differences			128.3
Uncovered energy costs consumed in operations			2
Deferred state income taxes			15.3
Deferred state income taxes			-5.4
Pension and other postretirement benefits			-1.4
Other			-4.7
Total net deferred income tax liabilities			$134.10
[1]	Reflects the settlement of Cove Point's existing deferred taxes at the time of the Offering.

Unit_Based_Compensation_Detail

Unit Based Compensation (Details) (Dominion Midstream LTIP, USD $)	1 Months Ended
In Millions, except Share data, unless otherwise specified	Oct. 31, 2014	Jan. 31, 2015
Share-based Goods and Nonemployee Services Transaction [Line Items]
Common units issued	2,322
Subsequent Event
Share-based Goods and Nonemployee Services Transaction [Line Items]
Common units issued		5,055
Other Operations And Maintenance Expense
Share-based Goods and Nonemployee Services Transaction [Line Items]
Recognized unit based compensation expense	0.1
Directors, Employees and Consultants of General Partner
Share-based Goods and Nonemployee Services Transaction [Line Items]
Common units available for delivery under Dominion Midstream 2014 LTIP	3,000,000

Operating_Segment_Narrative_De

Operating Segment (Narrative) (Details) (Corporate and Other, USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Net charge related to severance	$0
Predecessor
Segment Reporting Information [Line Items]
Net charge related to severance		$100,000

Operating_Segment_Schedule_of_

Operating Segment (Schedule of Segment Reporting Information, by Segment) (Details) (USD $)	3 Months Ended			12 Months Ended		3 Months Ended							10 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2014	Dec. 31, 2014		Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Oct. 19, 2014	Dec. 31, 2013		Dec. 31, 2012
Segment Reporting Information [Line Items]
Operating Revenue			$67.50	$313.30	[1]
Depreciation and amortization				37.7
Interest and related charges				0	[1]
Income tax expense				51.8	[2]
Net income	26.3	[3]	31.7	106.9
Net income attributable to limited partners subsequent to initial public offering	9.5
Capital expenditures				572.2
Total assets at December 31	2,258.40		2,258.40	2,258.40
Dominion Energy
Segment Reporting Information [Line Items]
Operating Revenue				313.3
Depreciation and amortization				37.7
Interest and related charges				0
Income tax expense				51.8
Net income	26.3
Net income attributable to limited partners subsequent to initial public offering	9.5
Capital expenditures				572.2
Total assets at December 31	2,258.40		2,258.40	2,258.40
Corporate and Other
Segment Reporting Information [Line Items]
Operating Revenue				0
Depreciation and amortization				0
Interest and related charges				0
Income tax expense				0
Net income	0
Net income attributable to limited partners subsequent to initial public offering	0
Capital expenditures				0
Total assets at December 31	0		0	0
Predecessor
Segment Reporting Information [Line Items]
Operating Revenue						65.7	111.2	68.9	67.5	104.2	67.1	104.7		343.5	[1]	293	[1]
Depreciation and amortization														31.7		33.3
Interest and related charges														0	[1]	0.1	[1]
Income tax expense														61.7		65.9
Net income				106.9		26.4	24.2	24.6	27.3	26.5	31.1	24.5	80.6	109.4		97.2
Capital expenditures														294.6		51.1
Total assets at December 31									1,498.20					1,498.20
Predecessor | Dominion Energy
Segment Reporting Information [Line Items]
Operating Revenue														343.5		293
Depreciation and amortization														31.7		33.3
Interest and related charges														0		0.1
Income tax expense														61.7		65.9
Net income				106.9										109.5		97.2
Capital expenditures														294.6		51.1
Total assets at December 31									1,498.20					1,498.20
Predecessor | Corporate and Other
Segment Reporting Information [Line Items]
Operating Revenue														0		0
Depreciation and amortization														0		0
Interest and related charges														0		0
Income tax expense														0		0
Net income				0										-0.1		0
Capital expenditures														0		0
Total assets at December 31									$0					$0
[1]	See Note 14 for amounts attributable to related parties.
[2]	Income taxes recognized prior to the Offering.
[3]	Allocation of net income attributable to partners' ownership interest subsequent to initial public offering has been adjusted for rounding.

Quarterly_Financial_and_Per_Un2

Quarterly Financial and Per Unit Data (Unaudited) (Details) (USD $)	3 Months Ended			12 Months Ended		0 Months Ended	3 Months Ended							10 Months Ended	12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2014	Dec. 31, 2014		Jan. 23, 2015	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Oct. 19, 2014	Dec. 31, 2013		Dec. 31, 2012
Effect of Fourth Quarter Events [Line Items]
Operating Revenue			$67.50	$313.30	[1]
Income from operations			36.9	158.7
Net income	26.3	[2]	31.7	106.9
Net income attributable to limited partners subsequent to initial public offering	9.5
Net income subsequent to initial public offering per unit (basic and diluted)
Net income subsequent to initial public offering per unit (basic and diluted)	$0.15
Distributions declared per unit	$0.14
Minimum
Net income subsequent to initial public offering per unit (basic and diluted)
Distributions declared per unit	$0.18
Subsequent Event
Net income subsequent to initial public offering per unit (basic and diluted)
Distributions declared per unit						$0.14
Distribution declared on Common unitholders and Subordinated unitholder						8.9
Common Units
Effect of Fourth Quarter Events [Line Items]
Net income attributable to limited partners subsequent to initial public offering	4.8	[2]
Net income subsequent to initial public offering per unit (basic and diluted)
Net income subsequent to initial public offering per unit (basic and diluted)	$0.15
Distribution declared on Common unitholders and Subordinated unitholder	4.5	[3],[4]
Subordinated Units
Effect of Fourth Quarter Events [Line Items]
Net income attributable to limited partners subsequent to initial public offering	4.7	[2]
Net income subsequent to initial public offering per unit (basic and diluted)
Net income subsequent to initial public offering per unit (basic and diluted)	$0.15
Distribution declared on Common unitholders and Subordinated unitholder	4.4	[3],[4]
Predecessor
Effect of Fourth Quarter Events [Line Items]
Operating Revenue							65.7	111.2	68.9	67.5	104.2	67.1	104.7		343.5	[1]	293	[1]
Income from operations							42.8	39.2	39.8	43.9	43	43.1	41.1		171.1		163.2
Net income				$106.90			$26.40	$24.20	$24.60	$27.30	$26.50	$31.10	$24.50	$80.60	$109.40		$97.20
[1]	See Note 14 for amounts attributable to related parties.
[2]	Allocation of net income attributable to partners' ownership interest subsequent to initial public offering has been adjusted for rounding.
[3]	On January 23, 2015, the Board of Directors of our general partner declared a prorated initial quarterly cash distribution of $0.1389 per unit, totaling $8.9 million, for the period subsequent to the Offering. This distribution was paid on February 13, 2015 to unitholders of record on February 3, 2015. The initial quarterly cash distribution was calculated as the minimum quarterly distribution of $0.1750 per unit prorated for the portion of the quarter subsequent to the Offering.
[4]	Allocation of distributions declared has been adjusted for rounding.