| Significant Accounting Policies (Policies) | 12 Months Ended |
| Dec. 31, 2017 |
| Accounting Policies [Abstract] | |
| Basis of Presentation | Basis of Presentation The contribution by Dominion Energy to Dominion Energy 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 Energy Midstream’s basis is equal to Dominion Energy’s cost basis in the general partner interest in Cove Point and a portion of the Preferred Equity Interest. As discussed in Note 16, Dominion Energy Midstream is the primary beneficiary of, and therefore consolidates, Cove Point. As such, Dominion Energy Midstream’s investment in the Preferred Equity Interest and Cove Point's preferred equity interest are eliminated in consolidation. Dominion Energy's retained common equity interest in Cove Point is reflected as noncontrolling interest. The Dominion Energy Questar Pipeline Acquisition is considered to be a reorganization of entities under common control. As a result, Dominion Energy Midstream’s basis in Dominion Energy Questar Pipeline is equal to Dominion Energy’s cost basis in the assets and liabilities of Dominion Energy Questar Pipeline. On December 1, 2016, Dominion Energy Questar Pipeline became a wholly-owned subsidiary of Dominion Energy Midstream and is therefore consolidated by Dominion Energy Midstream. The accompanying financial statements and related notes have been retrospectively adjusted to include the historical results and financial position of Dominion Energy Questar Pipeline beginning September 16, 2016, the inception date of common control. The DECG Acquisition is considered to be a reorganization of entities under common control. As a result, Dominion Energy Midstream’s basis in DECG is equal to Dominion Energy’s cost basis in the assets and liabilities of DECG. On April 1, 2015, DECG became a wholly-owned subsidiary of Dominion Energy Midstream and is therefore consolidated by Dominion Energy Midstream. The accompanying financial statements and related notes include the historical results and financial position of DECG beginning January 31, 2015, the inception date of common control. The financial statements for all years presented include costs for certain general, administrative and corporate expenses assigned by DES, DECGS (DEPC prior to January 1, 2016) or DEQPS to Dominion Energy Midstream on the basis of direct and allocated methods in accordance with Dominion Energy Midstream's services agreements with DES, DECGS (DEPC prior to January 1, 2016) and DEQPS. Where costs incurred cannot be determined by specific identification, the costs are allocated based on the proportional level of effort devoted by DES, DECGS (DEPC prior to January 1, 2016) or DEQPS resources that is attributable to the entities, determined by reference to number of employees, salaries and wages and other similar measures for the relevant DES, DECGS (DEPC prior to January 1, 2016) or DEQPS service. Management believes the assumptions and methodologies underlying the allocation of general corporate overhead expenses are reasonable. Dominion Energy Midstream reports one operating segment, Gas Infrastructure, which consists of gas transportation, LNG terminalling services and storage. In addition to Gas Infrastructure, Dominion Energy 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 or in allocating resources. See Note 25 for further discussions of Dominion Energy Midstream's operating segment. |
| 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 Energy 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 and affiliated receivables at December 31, 2017 and 2016 included $33.5 million and $50.6 million, respectively, of accrued unbilled revenue based on estimated amounts of services provided but not yet billed to its customers. See Note 22 for amounts related to affiliates. Cove Point renegotiated certain import-related contracts which resulted in annual payments in the years 2013 through 2016 totaling approximately $50 million. DECG 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 2018. At December 31, 2017, DECG has collected $14.5 million in facility charges, including $13.5 million collected subsequent to the DECG 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:
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Gas transportation and storage revenue
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Regulated gas sales
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Other revenue |
| 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 Energy 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 Energy 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 Energy 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 Energy Midstream would be taxed as a corporation. For the period October 20, 2014, through December 31, 2017, Dominion Energy Midstream’s qualifying income exceeded the required amount. The Consolidated Financial Statements reflect management’s conclusion that Dominion Energy Midstream’s status as a pass-through entity, if examined, would be sustained based on the technical merits of applicable tax law. DECG operated as a taxable corporation at the time of Dominion Energy’s acquisition of DECG. In March 2015, DECG 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 Energy's acquisition of DECG through March 2015 were included in the consolidated U.S. federal and certain state income tax returns of Dominion Energy. Dominion Energy Midstream's Consolidated Financial Statements reflect income taxes for the same period. Dominion Energy 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 the Dominion Energy Questar Combination through November 2016 were included in the consolidated U.S. federal and certain state income tax returns of Dominion Energy. Dominion Energy Midstream’s Consolidated Financial Statements reflect income taxes for the same period. Current income taxes for DECG and Dominion Energy 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 Energy’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 Energy Midstream's reported amounts of assets and liabilities exceeded tax bases by $1.5 billion at December 31, 2017. 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. The settlements of the federal and state net income tax payables and deferred income taxes of DECG and Dominion Energy Questar Pipeline are reflected as equity transactions in Dominion Energy 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, 2017 and 2016, accounts payable included $0.9 million and $0.3 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. |
| Restricted Cash | Restricted Cash Restricted cash includes customer deposits required under FERC gas tariffs and a distribution reserve. In October 2016, Cove Point fully funded a distribution reserve of $25.0 million, sufficient to pay two quarters of Preferred Return Distributions. In November 2017, $12.5 million was utilized to fund the quarterly Preferred Return Distribution. In February 2018, the remaining $12.5 million was utilized to fund the quarterly Preferred Return Distribution. |
| Derivative Instruments | Derivative Instruments Effective March 2017, Dominion Energy Midstream uses derivative instruments such as swaps to manage interest rate risks of its business operations. All derivatives, except those for which an exception applies, are required to be reported in the Consolidated Balance Sheets at fair value. Derivative contracts representing unrealized gain positions are reported as derivative assets. Derivative contracts representing unrealized losses are reported as derivative liabilities. Dominion Energy Midstream does not offset amounts recognized for the right to reclaim cash collateral or the obligation to return cash collateral against amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement. Dominion Energy Midstream had no margin assets or liabilities associated with cash collateral at December 31, 2017. See Note 9 for further information about derivatives. Derivative Instruments Designated as Hedging Instruments Dominion Energy Midstream has designated all of its derivative instruments as cash flow hedges for accounting purposes. For all derivatives designated as hedges, Dominion Energy Midstream formally documents the relationship between the hedging instrument and the hedged item, as well as the risk management objective and the strategy for using the hedging instrument. Dominion Energy Midstream assesses whether the hedging relationship between the derivative and the hedged item is highly effective at offsetting changes in cash flows both at the inception of the hedging relationship and on an ongoing basis. Any change in the fair value of the derivative that is not effective at offsetting changes in the cash flows of the hedged item is recognized currently in earnings. Hedge accounting is discontinued prospectively for derivatives that cease to be highly effective hedges. The cash flows from the cash flow hedge derivatives and from the related hedged items are classified in operating cash flows. Dominion Energy Midstream uses interest rate swaps to hedge its exposure to the variability of cash flows as a result of the variable interest rates on long-term debt. Changes in the fair value of the derivatives are reported in AOCI, to the extent they are effective at offsetting changes in the hedged item. Any derivative gains or losses reported in AOCI are reclassified to earnings when the forecasted item is included in earnings, or earlier, if it becomes probable that the forecasted transaction will not occur. Hedge accounting is discontinued if the occurrence of the forecasted transaction is no longer probable . Dominion Energy Midstream is exposed to the impact of market fluctuations in interest rate risks of its business operations. Dominion Energy Midstream uses derivative instruments to manage exposure to this risk, and has designated all of its derivative instruments as cash flow hedges for accounting purposes. See Note 8 for further information about fair value measurements and associated valuation methods for derivatives. Derivative assets and liabilities are presented gross on Dominion Energy Midstream's Consolidated Balance Sheets. Dominion Energy Midstream's derivative contracts include over-the-counter transactions. Over-the-counter contracts are bilateral contracts that are transacted directly with a third party. Certain over-the-counter contracts contain contractual rights of setoff through master netting arrangements, derivative clearing agreements, and contract default provisions. In addition, the contracts are subject to conditional rights of setoff through counterparty nonperformance, insolvency, or other conditions. |
| Investment in Equity Method Affiliates | Investment in Equity Method Affiliates Investments in affiliates where Dominion Energy 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 Energy 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 Energy 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 2017, 2016 and 2015, Dominion Energy Midstream capitalized interest costs and AFUDC of $10.8 million, $5.7 million and $2.0 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 Energy 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,
2017
2016
2015
(percent)
Storage
2.52
2.41
2.38
Transmission
2.89
2.93
3.15
Gas gathering and processing
5.06
5.04
—
General and other
6.32
8.05
7.01
In connection with its rate case filing in November 2016, Cove Point revised its depreciation rates effective January 2017, which resulted in an increase of $3.0 million to depreciation expense in 2017. Upon the approval of the rate case settlement agreement by FERC in 2017, depreciation rates were revised effective October 2017 reflecting a decrease of $3.0 million annually compared to the rates in effect through December 1, 2016. In 2017, this resulted in a $1.0 million decrease to depreciation expense in the Consolidated Statements of Income. |
| Long-Lived and Intangible Assets | Long-Lived and Intangible Assets Dominion Energy 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 Energy 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 Energy 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 Energy Midstream from other parties are reported as current assets and imbalances that Dominion Energy Midstream owes to other parties are reported within other current liabilities in the Consolidated Balance Sheets. |
| Debt Issuance Costs | Debt Issuance Costs Dominion Energy 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 Energy 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 Energy 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. Quarterly, Dominion Energy Midstream assesses its AROs to determine if circumstances indicate that estimates of the amounts or timing of future cash flows associated with retirement activities have changed. AROs are adjusted when significant changes in the amounts or timing of future cash flows are identified. Dominion Energy 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 Standard | New Accounting Standard 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 Energy Midstream, the revised accounting guidance is effective for interim and annual periods beginning January 1, 2018. We have completed the evaluation of the impact of this guidance and expect no significant impact on our results of operations. However, Dominion Energy Midstream will have offsetting decreases in operating revenues and purchased gas for fuel retained to offset costs on certain transportation and storage arrangements. Dominion Energy Midstream will apply the standard using the modified retrospective method as opposed to the full retrospective method. |
| Fair Value Measurements | Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (exit price) in an orderly transaction between market participants at the measurement date. However, the use of a mid-market pricing convention (the mid-point between bid and ask prices) is permitted. Fair values are based on assumptions that market participants would use when pricing an asset or liability, including assumptions about risk and the risks inherent in valuation techniques and the inputs to valuations. This includes not only the credit standing of counterparties involved and the impact of credit enhancements but also the impact of Dominion Energy Midstream's own nonperformance risk on its liabilities. Fair value measurements assume that the transaction occurs in the principal market for the asset or liability (the market with the most volume and activity for the asset or liability from the perspective of the reporting entity), or in the absence of a principal market, the most advantageous market for the asset or liability (the market in which the reporting entity would be able to maximize the amount received or minimize the amount paid). Dominion Energy Midstream applies fair value measurements to assets and liabilities associated with interest rate derivative instruments in accordance with the requirements discussed above. Credit adjustments are not considered material to the interest rate derivative fair values. Inputs and Assumptions Dominion Energy Midstream maximizes the use of observable inputs and minimizes the use of unobservable inputs when measuring fair value. Fair value is based on actively-quoted market prices, if available. In the absence of actively-quoted market prices, price information is sought from external sources, including broker quotes and industry publications. When evaluating pricing information provided by brokers and other pricing services, Dominion Energy Midstream considers whether the broker is willing and able to trade at the quoted price, if the broker quotes are based on an active market or an inactive market and the extent to which brokers are utilizing a particular model if pricing is not readily available. If pricing information from external sources is not available, or if Dominion Energy Midstream believes that observable pricing is not indicative of fair value, judgment is required to develop the estimates of fair value. In those cases, Dominion Energy Midstream must estimate prices based on available historical and near-term future price information that reflect its market assumptions. The inputs and assumptions used in measuring fair value for interest rate derivative contracts include the following:
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Interest rate curves
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Credit quality of counterparties and Dominion Energy Midstream
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Notional value
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Credit enhancements
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Time value Levels Dominion Energy Midstream also utilizes the following fair value hierarchy, which prioritizes the inputs to valuation techniques used to measure fair value into three broad levels:
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Level 1-Quoted prices (unadjusted) in active markets for identical assets and liabilities that it has the ability to access at the measurement date.
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Level 2-Inputs other than quoted prices included within Level 1 that are either directly or indirectly observable for the asset or liability, including quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in inactive markets, inputs other than quoted prices that are observable for the asset or liability, and inputs that are derived from observable market data by correlation or other means. Instruments categorized in Level 2 include interest rate swaps.
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Level 3-Unobservable inputs for the asset or liability, including situations where there is little, if any, market activity for the asset or liability. The fair value hierarchy gives the highest priority to quoted prices in active markets (Level 1) and the lowest priority to unobservable data (Level 3). In some cases, the inputs used to measure fair value might fall in different levels of the fair value hierarchy. In these cases, the lowest level input that is significant to a fair value measurement in its entirety determines the applicable level in the fair value hierarchy. Assessing the significance of a particular input to the fair value measurement in its entirety requires judgment, considering factors specific to the asset or liability. For derivative contracts, Dominion Energy Midstream recognizes transfers among Level 1, Level 2 and Level 3 based on fair values as of the first day of the month in which the transfer occurs. Transfers out of Level 3 represent assets and liabilities that were previously classified as Level 3 for which the inputs became observable for classification in either Level 1 or Level 2. |
| Commitments and Contingencies | As a result of issues generated in the ordinary course of business, Dominion Energy 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 Energy Midstream to estimate a range of possible loss. For such matters that Dominion Energy 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 Energy Midstream is able to estimate a range of possible loss. For legal proceedings and governmental examinations for which Dominion Energy 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 Energy 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 Energy Midstream’s financial position, liquidity or results of operations. |
