| Significant Accounting Policies (Policies) | 12 Months Ended |
| Dec. 31, 2016 |
| Accounting Policies [Abstract] | |
| Basis of Presentation | Basis of Presentation The contribution by Dominion to Dominion Midstream of the general partner interest in Cove Point and a portion of the Preferred Equity Interest is considered to be a reorganization of entities under common control. As a result, Dominion Midstream’s basis is equal to Dominion’s cost basis in the general partner interest in Cove Point and a portion of the Preferred Equity Interest. As discussed in Note 14, Dominion Midstream is the primary beneficiary of, and therefore consolidates, Cove Point. As such, Dominion Midstream’s investment in the Preferred Equity Interest and Cove Point's preferred equity interest are eliminated in consolidation. Dominion's retained common equity interest in Cove Point is reflected as noncontrolling interest. The Questar Pipeline Acquisition is considered to be a reorganization of entities under common control. As a result, Dominion Midstream’s basis in Questar Pipeline is equal to Dominion’s cost basis in the assets and liabilities of Questar Pipeline. On December 1, 2016, Questar Pipeline became a wholly-owned subsidiary of Dominion Midstream and is therefore consolidated by Dominion Midstream. The accompanying financial statements and related notes have been retrospectively adjusted to include the historical results and financial position of Questar Pipeline beginning September 16, 2016, the inception date of common control. The DCG Acquisition is considered to be a reorganization of entities under common control. As a result, Dominion Midstream’s basis in DCG is equal to Dominion’s cost basis in the assets and liabilities of DCG. On April 1, 2015, DCG became a wholly-owned subsidiary of Dominion Midstream and is therefore consolidated by Dominion Midstream. The accompanying financial statements and related notes include the historical results and financial position of DCG beginning January 31, 2015, the inception date of common control. For the period 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 for accounting purposes. 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 periods 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, comprehensive 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 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, DCGS (Dominion Payroll prior to January 1, 2016) or QPC Services Company to Dominion Midstream and Cove Point on the basis of direct and allocated methods in accordance with Dominion Midstream's services agreements with DRS, DCGS (Dominion Payroll prior to January 1, 2016) and QPC Services Company and Cove Point's services agreement 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, DCGS (Dominion Payroll prior to January 1, 2016) or QPC Services Company 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, DCGS (Dominion Payroll prior to January 1, 2016) or QPC Services Company service. 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. |
| Combination of Entities under Common Control | The contribution by Dominion to Dominion Midstream of the general partner interest in Cove Point and a portion of the Preferred Equity Interest is considered to be a reorganization of entities under common control. As a result, Dominion Midstream’s basis is equal to Dominion’s cost basis in the general partner interest in Cove Point and a portion of the Preferred Equity Interest. As discussed in Note 14, Dominion Midstream is the primary beneficiary of, and therefore consolidates, Cove Point. As such, Dominion Midstream’s investment in the Preferred Equity Interest and Cove Point's preferred equity interest are eliminated in consolidation. Dominion's retained common equity interest in Cove Point is reflected as noncontrolling interest. The Questar Pipeline Acquisition is considered to be a reorganization of entities under common control. As a result, Dominion Midstream’s basis in Questar Pipeline is equal to Dominion’s cost basis in the assets and liabilities of Questar Pipeline. On December 1, 2016, Questar Pipeline became a wholly-owned subsidiary of Dominion Midstream and is therefore consolidated by Dominion Midstream. The accompanying financial statements and related notes have been retrospectively adjusted to include the historical results and financial position of Questar Pipeline beginning September 16, 2016, the inception date of common control. The DCG Acquisition is considered to be a reorganization of entities under common control. As a result, Dominion Midstream’s basis in DCG is equal to Dominion’s cost basis in the assets and liabilities of DCG. On April 1, 2015, DCG became a wholly-owned subsidiary of Dominion Midstream and is therefore consolidated by Dominion Midstream. The accompanying financial statements and related notes include the historical results and financial position of DCG beginning January 31, 2015, the inception date of common control. |
| Segment Reporting | Dominion Midstream reports one operating segment, Dominion Energy, which consists of gas transportation, LNG import 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 23 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. Dominion Midstream is currently generating significant revenue and earnings from annual reservation payments under long-term regasification, firm peaking storage and firm transportation contracts. Straight-fixed-variable rate designs are used to allow for recovery of substantially all fixed costs in demand or reservation charges, thereby reducing the earnings impact of volume changes on gas transportation and storage operations. Customer receivables at December 31, 2016 and 2015 included $50.6 million and $19.9 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 resulted in annual payments in the years 2013 through 2016 totaling approximately $50 million . DCG collects facility charges related with certain of its expansion projects. These facility charges are expected to total approximately $15.5 million and will be collected in the years 2014 through 2017. At December 31, 2016, DCG has collected $14.0 million in facility charges, including $13.0 million collected subsequent to the DCG Acquisition. These facility charges are amortized to revenue over the term of the related transportation contract once the related projects have been placed into service. 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 FERC-regulated sales of storage and transmission services; • Regulated gas sales consist primarily of FERC-regulated natural gas sales; and • Other revenue consists primarily of sales of purchased gas retained for use in routine operations and LNG cargoes 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, 2016, 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 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. DCG operated as a taxable corporation at the time of Dominion’s acquisition of DCG. In March 2015, DCG converted to a single member limited liability company and as a result, became a disregarded entity for income tax purposes and was treated as a taxable division of its corporate parent. Its business activities from the time of Dominion's acquisition of DCG through March 2015 were included in the consolidated U.S. federal and certain state income tax returns of Dominion. Dominion Midstream's Consolidated Financial Statements reflect income taxes for the same period. Questar Pipeline is a disregarded entity for income tax purposes and was treated as a taxable division of its corporate parent. Its business activities from the time of Dominion’s acquisition of Dominion Questar through November 2016 will be included in the consolidated U.S. federal and certain state income tax returns of Dominion. Dominion Midstream’s Consolidated Financial Statements reflect income taxes for the same period. Current income taxes for Cove Point, DCG and Questar Pipeline 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. Dominion Midstream's reported amounts of assets and liabilities exceeded tax bases by $1.4 billion at December 31, 2016. 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 payroll and taxes on the Consolidated Balance Sheets. Under Dominion’s tax sharing agreement, federal and state income taxes of $38.6 million were paid to Dominion and DCPI for the year ended December 31, 2014. In addition, the settlements of the federal and state net income tax payables and deferred income taxes of Cove Point, DCG and Questar Pipeline are reflected as equity transactions 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, 2016 and 2015, accounts payable included $0.3 million and $0.8 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. |
| Investment in Equity Method Affiliates | Investment in Equity Method Affiliates Investments in affiliates where Dominion Midstream exercises significant influence over the operating activities of the entity, but does not control the entity, are accounted for using the equity method. Such investments are included in investment in equity method affiliates in the Consolidated Balance Sheets. Dominion Midstream records equity method adjustments in earnings from equity method affiliates in the Consolidated Statements of Income, including its proportionate share of investee income or loss and other adjustments required by the equity method. Dominion Midstream periodically evaluates its equity method investments to determine whether a decline in fair value should be considered other-than-temporary. If a decline in fair value of an investment is determined to be other-than-temporary, the investment is written down to its fair value at the end of the reporting period. |
| 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 2016, 2015 and 2014, Dominion Midstream capitalized interest costs and AFUDC of $5.7 million , $2.0 million and $0.1 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, 2016 2015 2014 (percent) Storage 2.41 2.38 2.39 Transmission 2.93 3.15 2.81 Gas gathering and processing 5.04 General and other 8.05 7.01 4.09 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 connection with its rate case filing in November 2016, Cove Point revised its depreciation rates effective January 2017. The estimated annual impact is a $4.1 million increase to depreciation expense. |
| 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 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 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 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 FERC, legislation or historical experience, as well as discussions with FERC and legal counsel. 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. |
| Inventories | Inventories Materials and supplies and gas stored 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 the tariff for each regulated entity. Imbalances are settled in-kind and in cash. 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. |
| Debt Issuance Costs | Debt Issuance Costs Dominion Midstream defers and amortizes debt issuance costs over the expected lives of the respective debt issues, considering maturity dates and, if applicable, redemption rights held by others. Deferred debt issuance costs are recorded as a reduction of long-term debt in the Consolidated Balance Sheets. Amortization of the issuance costs is reported as interest expense. Unamortized costs associated with the redemptions of debt securities prior to stated maturity dates are generally recognized and recorded in interest expense immediately. As permitted by regulatory authorities, gains or losses resulting from the refinancing of debt allocable to utility operations subject to cost-based rate regulation are deferred and amortized over the lives of the new issuances. |
| 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 a reporting unit below its carrying value. |
| Asset Retirement Obligations | Asset Retirement Obligations Dominion Midstream recognizes AROs at fair value as incurred or when sufficient information becomes available to determine a reasonable estimate of the fair value of future retirement activities to be performed, for which a legal obligation exists. These amounts are generally capitalized as costs of the related tangible long-lived assets. Since relevant market information is not available, fair value is estimated using discounted cash flow analyses. Periodically, Dominion Midstream evaluates the key assumptions underlying its AROs including estimates of the amounts and timing of future cash flows associated with retirement activities. AROs are adjusted when significant changes in these assumptions are identified. Dominion Midstream reports accretion of AROs and depreciation on asset retirement costs associated with its natural gas pipeline assets as an adjustment to the related regulatory liabilities when revenue is recoverable from customers for AROs. |
| New Accounting Standards | New Accounting Standards In May 2014, the FASB issued revised accounting guidance for revenue recognition from contracts with customers. The core principle of this revised accounting guidance is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The amendments in this update also require disclosure of the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. For Dominion Midstream, the revised accounting guidance is effective for interim and annual periods beginning January 1, 2018. We have completed the preliminary stages of evaluating the impact of this guidance and, pending evaluation of the item discussed below expect no significant impact on our results of operations. Now that our preliminary evaluation is complete, we will expand the scope of our assessment to include all contracts with customers. In addition, we are considering certain issues including recognition of revenue in contracts with variable consideration. Dominion Midstream intends to apply the standard using the modified retrospective method as opposed to the full retrospective method. |
| Commitments and Contingencies | As a result of issues generated in the ordinary course of business, Dominion Midstream is involved in legal proceedings before various courts and is periodically subject to governmental examinations (including by FERC), inquiries and investigations. Certain legal proceedings and governmental examinations involve demands for unspecified amounts of damages, are in an initial procedural phase, involve uncertainty as to the outcome of pending appeals or motions, or involve significant factual issues that need to be resolved, such that it is not possible for Dominion Midstream to estimate a range of possible loss. For such matters that Dominion Midstream cannot estimate, a statement to this effect is made in the description of the matter. Other matters may have progressed sufficiently through the litigation or investigative processes such that Dominion Midstream is able to estimate a range of possible loss. For legal proceedings and governmental examinations for which Dominion Midstream is able to reasonably estimate a range of possible losses, an estimated range of possible loss is provided, in excess of the accrued liability (if any) for such matters. Estimated ranges of loss are inclusive of legal fees and net of any anticipated insurance recoveries. Any estimated range is based on currently available information and involves elements of judgment and significant uncertainties. Any accrued liability is recorded on a gross basis with a receivable also recorded for any probable insurance recoveries. Any estimated range of possible loss may not represent Dominion Midstream’s maximum possible loss exposure. The circumstances of such legal proceedings and governmental examinations will change from time to time and actual results may vary significantly from the current estimate. Management does not anticipate that the liabilities, if any, arising from such proceedings would have a material effect on Dominion Midstream’s financial position, liquidity or results of operations. |
| Credit Risk | Credit risk is the risk of financial loss if counterparties fail to perform their contractual obligations. In order to minimize overall credit risk, credit policies are maintained, including the evaluation of counterparty financial condition. In addition, counterparties may make available collateral, including letters of credit, payment guarantees, or cash deposits. |
