| Summary of Significant Accounting Policies (Policies) | 12 Months Ended |
| Dec. 31, 2019 |
| Accounting Policies [Abstract] | |
| Basis of Presentation | Basis of Presentation Our consolidated financial statements have been prepared under the rules and regulations of the Securities and Exchange Commission (“SEC”). These rules and regulations conform to the accounting principles contained in the Financial Accounting Standards Board’s (“FASB”) Accounting Standards Codification, the single source of accounting principles generally accepted in the United States (“GAAP”). Prior to the IPO on October 30, 2017, our financial position, results of operations and cash flows consisted of the Predecessor's operations, which represented a combined reporting entity. All intercompany accounts and transactions within the Predecessor’s financial statements have been eliminated for all periods presented. The assets and liabilities contributed to us by the Predecessor have been reflected on the historical cost basis on the consolidated financial statements. Immediately prior to the IPO, the Predecessor’s assets and liabilities were transferred to the Partnership within our Parent’s consolidated group in a transaction under common control. Subsequent to the IPO, our financial position, results of operations and cash flows consist of consolidated BP Midstream Partners LP activities and balances. Prior to the IPO, our consolidated statements of operations also include expense allocations to the Predecessor for certain functions performed by our Parent on our behalf, including allocations of general corporate expenses related to finance, accounting, treasury, legal, information technology, human resources, shared services, government affairs, insurance, health, safety, security, employee benefits, incentives, severance and environmental functional support. The portion of expenses that are specifically identifiable to the Wholly Owned Assets are directly recorded to the Predecessor, with the remainder allocated on the basis of headcount, throughput volumes, miles of pipe and other measures. Our management believes the assumptions underlying the financial statements, including the assumptions regarding the allocation of general corporate expenses from our Parent, are reasonable. Nevertheless, the financial statements may not include all of the expenses that would have been incurred, had we been a stand-alone entity during the periods prior to the IPO and may not reflect our financial position, results of operations and cash flows, had we been a stand-alone entity during such periods. See Note 10 - Related Party Transactions . Prior to the IPO, the Wholly Owned Assets did not own or maintain separate bank accounts. Our Parent used a centralized approach to cash management and historically funded our operating and investing activities as needed within the boundaries of a documented funding agreement. Accordingly, cash held by our Parent at the corporate level was not allocated to us for any of the periods prior to the IPO. During such periods, we reflected the cash generated by our operations and expenses paid by our Parent on our behalf as a component of Net parent investment on our consolidated balance sheets, and as a net distribution to our Parent on our consolidated statements of cash flows. We also did not include any interest income on the net cash transfers to our Parent. In connection with the IPO, we established our own cash accounts for the funding of our operating and investing activities. See Note 3 - Acquisitions for additional details. All financial information presented for the periods after the IPO represents the consolidated results of operations, financial position and cash flows of the Partnership. Accordingly: • Our consolidated statements of operations and cash flows for the years ended December 31, 2019 and 2018 consist of the consolidated results of the Partnership. Our consolidated statements of operations and cash flows for the year ended December 31, 2017 consist of the consolidated results of the Partnership for the period from October 30, 2017 through December 31, 2017, and the combined results of the Predecessor for the period from January 1, 2017 through October 29, 2017. • Our consolidated balance sheet at December 31, 2019 and 2018 consist of the consolidated balances of the Partnership. |
| Principles of Consolidation | Principles of Consolidation Our consolidated financial statements include all subsidiaries, where the Partnership has control and a variable interest entity ("VIE") of which we are the primary beneficiary. The assets and liabilities in the consolidated financial statements have been reflected on a historical basis. All inter-company accounts and transactions are eliminated upon consolidation. We evaluate our ownership, contractual arrangements and other interests in entities to determine if these entities are VIEs and whether we are the primary beneficiary of the VIE. In determining whether we are the primary beneficiary of a VIE and therefore required to consolidate the VIE, we apply a qualitative approach that determines whether we have both (1) the power to direct the activities of the VIE that most significantly impact the economic performance and (2) the obligation to absorb the majority of losses of or the rights to receive the majority of the benefits from the VIE that could potentially be significant to the VIE. We continuously assess whether we are the primary beneficiary of a VIE as changes to existing relationships or future transactions may result in the consolidation or deconsolidation, as the case may be, of such VIE. We consolidate BP2, River Rouge and Diamondback, as we control these entities through 100% of the ownership interest. We control and consolidate Mardi Gras via an agreement between us and our Parent, under which we have the right to vote 100% of Mardi Gras' interests in each of the Mardi Gras Joint Ventures. We have determined that we are the primary beneficiary of Mardi Gras. See Note 17 - Variable Interest Entity for further discussion. |
| Net Parent Investment | Net Parent Investment Net parent investment represents our Parent’s historical investment in us, our accumulated net earnings after taxes, and the net effect of transactions with and allocations from our Parent through October 29, 2017. |
| Use of Estimates | Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported on the consolidated financial statements and disclosures included in the accompanying notes. Actual results could differ from these estimates. |
| Common Control Transactions | Common Control TransactionsAssets and businesses acquired from our Parent and its subsidiaries are accounted for as common control transactions whereby the net assets acquired are included in our consolidated balance sheets at their historical carrying value. If any recognized consideration transferred in such a transaction exceeds the historical carrying value of the net assets acquired, the excess is treated as a capital distribution to our Parent, similar to a dividend. If the historical carrying value of the net assets acquired exceeds any recognized consideration transferred including, if applicable, the fair value of any limited partner units issued, such excess is treated as a capital contribution from our Parent. |
| Revenue Recognition | Revenue Recognition We adopted Accounting Standards Codification (“ASC”) Topic 606, Revenue from Contracts with Customers (“ASC 606”), applying the modified retrospective transition method, which required us to apply the new standard to (i) all revenue contracts entered into, and (ii) revenue contracts which were not completed as of January 1, 2018. ASC 606 replaces existing revenue recognition requirements in GAAP and requires us to recognize revenue at an amount that reflects the consideration to which we expect to be entitled in exchange for transferring goods or services to a customer. ASC 606 also requires certain disclosures regarding qualitative and quantitative information regarding the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. The adoption of ASC 606 did not result in a transition adjustment nor did it have a material impact on the timing or amount of our revenue recognition. Please see Note 4 - Revenue Recognition for further discussion. |
| Equity Method Investments | Equity Method Investments We account for an investment under the equity method if we have the ability to exercise significant influence, but not control, over the investee. Under the equity method of accounting, the investment is recorded at its initial carrying value on the consolidated balance sheets and is adjusted for capital contributions, dividends received and our share of the investee’s earnings or losses, which is recorded as a component of Income from equity method investments on the consolidated statements of operations. We evaluate equity method investments for impairment when events or changes in circumstances indicate, in our management’s judgment, that a decline in value is other than temporary. Factors that may indicate that a decline in value is other than temporary include a deterioration in the financial condition of the investee, decisions to sell the investee, significant losses incurred by the investee, a change in the economic environment that is expected to adversely affect the investee’s operations, an investee’s loss of a principal customer or supplier and an investee’s recording of impairment charges. If we determine that a decline in value is other than temporary, the investment is written down to its fair value, which establishes the investment’s new cost basis. |
| Property, plant and equipment | Property, plant and equipment Our property, plant and equipment is recorded at its historical cost of construction, or the carrying value of the transferring entity in a transaction under common control, or at fair value in a business combination. We record depreciation using the straight-line method with the following useful lives: Depreciable Land — ROW assets — Buildings and improvements 16 - 40 Pipelines and equipment 17 - 40 Other 4 - 23 Construction in progress — Upon the sale or retirement of property, plant and equipment, the cost and related accumulated depreciation are removed, and any resulting gain or loss is recorded on the consolidated statements of operations. Ordinary maintenance and repair costs are generally expensed as incurred. Such costs are recorded in Maintenance expenses- third parties and Maintenance expenses-related parties on our consolidated statements of operations. Costs of major renewals, betterments and replacements are capitalized as Property, plant and equipment. For constructed assets, we capitalize all construction-related direct labor and material costs, as well as indirect construction costs. |
| Impairment of Long-lived Assets | Impairment of Long-lived AssetsWe evaluate long-lived assets of identifiable business activities for impairment when events or changes in circumstances indicate, in our management’s judgment, that the carrying value of such assets may not be recoverable. These events include market declines that are believed to be other than temporary, changes in the manner in which we intend to use a long-lived asset, decisions to sell an asset and adverse changes in the legal or business environment, such as adverse actions by regulators. If an event occurs, which is a determination that involves judgment, we evaluate the recoverability of our carrying values of an asset group based on the long-lived assets’ ability to generate future cash flows on an undiscounted basis. If the carrying amount is higher than the undiscounted cash flows, we further evaluate the impairment loss by comparing management’s estimate of the fair value of the assets to the carrying value of such assets. We record a loss for the amount that the carrying value exceeds the estimated fair value. |
| Cash Equivalents | Cash Equivalents Cash equivalents are highly liquid, short-term investments that are readily convertible to known amounts of cash and will mature within 90 days or less from the date of acquisition. We record cash equivalents, if any, at its carrying value, which approximates its fair value. |
| Accounts Receivable and Allowance for Doubtful Accounts | Accounts Receivable and Allowance for Doubtful AccountsAccounts receivable represent valid claims against customers for services rendered, net of allowances for doubtful accounts. We assess the creditworthiness of our counterparties on an ongoing basis and require security, including prepayments and other forms of collateral, when appropriate. We establish provisions for losses on accounts receivable due from shippers if we determine that we will not collect all or part of the outstanding balance. Outstanding customer receivables are regularly reviewed for possible nonpayment indicators, and allowances for doubtful accounts are recorded based upon management’s estimate of collectability at each balance sheet date. At December 31, 2019 and 2018, our allowance for doubtful account balances were zero. |
| Income Taxes | Income Taxes Prior to the IPO on October 30, 2017, the Predecessor was not a standalone entity for income tax purposes and was included as part of BPA federal income tax returns. Our provision for income taxes was prepared on a separate return basis with consideration to the tax laws and rates applicable in the jurisdictions in which we operated and earned income. We used the asset and liability method of accounting for income taxes. Under the asset and liability method, deferred tax assets and liabilities were recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of the existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities were measured by applying the expected enacted income tax rates to taxable income in the years in which those differences were expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in income tax rates was recognized in the results of operations in the period that included the enactment date. The realizability of deferred tax assets was evaluated quarterly based on a “more likely than not” standard and, to the extent this threshold was not met, a valuation allowance would be recorded. Prior to the IPO, we would recognize the impact of an uncertain tax position only if it was more likely than not of being sustained upon examination by the relevant taxing authority based on the technical merits of the position. There were no uncertain tax positions recorded for the Predecessor at the end of each period presented. Had there been any uncertain tax positions, our policy was to classify interest and penalties as a component of income tax expense. BP Midstream Partners LP is treated as a partnership for federal and state income tax purposes, with each partner being separately taxed on its share of taxable income. Therefore, we have excluded income taxes from these financial statements subsequent to the IPO date of October 30, 2017. The deferred tax liability of the Predecessor was removed from our consolidated balance sheets with an offset to equity at that date. We are a partnership, which is not subject to U.S. federal income taxes. Rather, our taxable income flows through to the owners, who are responsible for paying the applicable income taxes on the income allocated to them. For tax years beginning on or after January 1, 2018, we are subject to partnership audit rules enacted as part of the Bipartisan Budget Act of 2015 (the “Centralized Partnership Audit Regime”). Under the Centralized Partnership Audit Regime, any IRS audit of the Partnership would be conducted at the Partnership level, and if the IRS determines an adjustment, the default rule is that we would pay an “imputed underpayment” including interest and penalties, if applicable. We may instead elect to make a “push-out” election, in which case the partners for the year that is under audit would be required to take into account the adjustments on their own personal income tax returns. |
| Asset Retirement Obligations | Asset Retirement Obligations Asset retirement obligations represent legal and constructive obligations associated with the retirement of long-lived assets that result from the acquisition, construction, development and/or normal use of the asset. We record liabilities for obligations related to the retirement and removal of long-lived assets used in our businesses at fair value on a discounted basis when they are incurred and can be reasonably estimated. Amounts recorded for the related assets are increased by the amount of these obligations. Over time, the liabilities increase due to the change in their present value, and the initial capitalized costs are depreciated over the useful lives of the related assets. The liabilities are eventually extinguished when settled at the time the asset is taken out of service. Although the Wholly Owned Assets will be replaced as needed, the pipelines will continue to exist for an indefinite period of time. Therefore, there is uncertainty around the asset retirement settlement dates. As a result, we determined that there is not sufficient information to make a reasonable estimate of the asset retirement obligations for the Wholly Owned Assets, and we did not recognize any asset retirement obligations as of December 31, 2019 and 2018. |
| Legal | Legal We are subject to litigation and regulatory proceedings as the result of our business operations and transactions. We utilize both internal and external counsel in evaluating our potential exposure to adverse outcomes from orders, judgments or settlements. In general, we expense legal costs as incurred. |
| Environmental Matters | Environmental Matters We are subject to federal, state, and local environmental laws and regulations. These laws require us to take future action to remediate the effects on the environment of prior disposal or release of chemicals or petroleum substances by us or other parties. Environmental expenditures that are required to obtain future economic benefits from its assets are capitalized as part of those assets. Expenditures that relate to an existing condition caused by past operations and that do not contribute to current or future earnings shall be expensed, unless already provisioned for, which then shall be charged against provisions. Provisions are recognized when we have a present legal or constructive obligation as a result of a past event, if it is probable that an outflow of resources embodying economic benefits will be required to settle the obligation and a reliable estimate can be made of the amount of the obligation. We do not discount environmental liabilities, and we record environmental liabilities when environmental assessments and/or remedial efforts are probable, and when we can reasonably estimate the costs. In making environmental liability estimations, we consider the material effect of environmental compliance, pending legal actions against us and potential third-party liability claims. Often, as the remediation evaluation and effort progresses, additional information is obtained, requiring revisions to estimated costs. Generally, our recording of these provisions coincides with our commitment to a formal plan of action, or if earlier, on the closure or divestment of inactive sites. We recognize receivables for anticipated associated insurance recoveries when such recoveries are deemed to be probable. The ultimate requirement for remediation and its cost are inherently difficult to estimate. We believe that the outcome of these uncertainties should not have a material adverse effect on our financial condition, cash flows, or operating results. Our existing environmental conditions prior to the IPO are obligations contributed to us by the prior operator of these facilities, BP Pipelines, who has agreed to indemnify us with respect to such conditions under the terms of an omnibus agreement that we entered into in connection with the IPO. For provisions related to such conditions, we record indemnification assets in our consolidated balance sheets in the amounts that equal the provisions. Subsequent to the IPO, revisions to the estimated environmental liability for conditions that are not indemnified under the omnibus agreement with our Parent are reflected in our consolidated statements of operations when they are probable and reasonably estimable. For additional information regarding our environmental matters, see Note 14 - Commitments and Contingencies . |
| Other Contingencies | Other Contingencies We recognize liabilities for contingencies when we have an exposure that indicates it is both probable that a liability has been incurred and the amount of loss can be reasonably estimated. Where the most likely outcome of a contingency can be reasonably estimated, we accrue a liability for that amount. Where the most likely outcome cannot be estimated, a range of potential losses is established and if no one amount in that range is more likely than any other, the lower end of the range is accrued. To the extent that actual outcomes differ from our estimates, or additional facts and circumstances cause us to revise our estimates, our earnings will be affected. |
| Fair Value Estimates | Fair Value Estimates Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. We categorize assets and liabilities measured at fair value into one of three levels depending on the ability to observe inputs employed in their measurement: • Level 1 inputs are quoted prices in active markets for identical assets or liabilities. • Level 2 inputs are inputs that are observable, either directly or indirectly, other than quoted prices included within level 1 for the asset or liability. • Level 3 inputs are unobservable inputs for the asset or liability reflecting significant modifications to observable related market data or our assumptions about pricing by market participants. |
| Net Income per Unit | Net Income per UnitNet 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 for the period subsequent to the IPO by the weighted average number of common units and subordinated units, respectively, outstanding for the period. Because we have more than one class of participating securities, we use the two-class method when calculating the net income per unit applicable to limited partners. The classes of participating securities include common units, subordinated units and incentive distribution rights. |
| Unit-Based Compensation | Unit-Based Compensation The fair value of phantom unit awards granted to non-employee directors is based on the fair market value of our common units on the date of grant. Our unit-based compensation expenses are recognized ratably over the vesting term of the awards. We have elected to recognize the impact of forfeitures only when they occur. |
| Recent Accounting Pronouncements | Accounting Pronouncements Adopted in 2019 As of January 1, 2019, we adopted ASU 2016-02, “Leases” utilizing the modified retrospective approach. The adoption required the recognition of a lease liability and a corresponding lease asset for virtually all lease contracts. It also required additional disclosures about leasing arrangements. The adoption of ASC 842 resulted in the recognition of approximately $0.6 million in right-of-use assets and the same amount of lease liability on our balance sheet for the present value of the rights and obligations. We have elected the optional practical expedients permitted under the transition guidance within the new lease standard, which among other things, allows us to carry forward the historical accounting treatment relating to classification for existing leases upon adoption, allows us to not be required to reassess whether an expired or existing contract is or contains a lease, and allows us not to have to reassess initial direct costs for an existing lease. In addition, we elected the optional transition guidance related to land easements that allows us to carry forward our historical accounting treatment on existing agreements upon adoption. This allowed us to not be required to assess existing land easements that were not historically accounted for as leases under Topic 840, therefore they are excluded from this disclosure. |
| Revenue Recognition | Revenue Recognition Topic 606 requires entities to recognize revenue through the application of a five-step model, which includes: (1) identification of the contract; (2) identification of the performance obligations; (3) determination of the transaction price; (4) allocation of the transaction price to the performance obligations; and (5) recognition of revenue as the entity satisfies the performance obligations. Under Topic 606, we recognize revenue over time or at a point in time, depending on the nature of the performance obligations contained in the respective contract with our customer. A performance obligation is our unit of account and it represents a promise in a contract to transfer goods or services to the customer. The contract transaction price, which is the amount of consideration to which an entity expects to be entitled in exchange for transferring promised goods or services to a customer, is allocated to each performance obligation and recognized as revenue when or as the performance obligation is satisfied. The following is an overview of our significant revenue stream, including a description of the respective performance obligations and related methods of revenue recognition. Pipeline Transportation Revenue from pipeline transportation is comprised of tariffs and fees associated with the transportation of liquid petroleum products, generally at published tariffs and in certain instances, revenue from minimum volume commitment contracts at negotiated rates. Tariff revenue is recognized either at the point of delivery or at the point of receipt, pursuant to specifications outlined in the respective tariffs. We record revenue for crude oil, refined products and diluent transportation over the period in which they are earned (i.e., either physical delivery of product has taken place or the services designated in the contract have been performed.) Our services are typically billed on a monthly basis, and we generally do not offer extended payment terms. We accrue revenue based on services rendered but not billed for that accounting month. Billings to BP Products for deficiency volumes under its minimum volume commitments, if any, are recorded as deferred revenue and credits, a contract liability, on our consolidated balance sheets, as BP Products has the right to make up the deficiency volumes within the measurement period specified by the agreements. Deferred revenue under these arrangements is recognized into revenue once it is deemed remote that the customer will meet its required annual minimum volume commitments. If the customer does satisfy its minimum volume commitment by shipping the deficiency volumes within the same calendar year, it may receive a refund of excess payments. Allowance Oil Our tariff for crude oil transportation at BP2 includes a fixed loss allowance (“FLA”). An FLA factor per barrel, a fixed percentage, is a separate fee that is considered a part of the transaction price under the applicable crude oil tariff to cover evaporation and other losses in transit. The fixed product loss allowance factor intends to cover evaporation, crude viscosity, temperature differences and other losses in transit. Revenue related to allowance oil sales is recognized as a part of the transportation revenue from the shipper during the month the throughput volume is transported on the pipeline. The amount of revenue recognized is a product of the quantity transported, the applicable FLA factor and the settlement price during the month the product is transported. The settlement price for volumes accumulated prior to October 1, 2017 was a summation of the calendar-month average of West Texas Intermediate (“WTI”) on the New York Mercantile Exchange and a differential provided by our Parent. The differential represents the difference in market price between WTI and the type of allowance oil to be settled and the difference in market price between the settlement month and the month prior to settlement. The fluctuation in commodity prices between the month of movement and the month of settlement resulted in an embedded derivative, which we measured along with the allowance oil receivable in their entirety at fair value because the economic characteristics and risks of the embedded derivative were clearly and closely related to the economic characteristics and risks of the host arrangement. The allowance oil volumes accumulated prior to October 1, 2017 were entirely settled upon October 30, 2017. While such volumes were outstanding, we recognized the changes in their fair value in Other income on the consolidated statements of operations. The embedded derivative was not designated as a hedging instrument. The settlement price for volumes accumulated on and after October 1, 2017 is determined using the same equation as the prior periods but with pricing input from the month of movement, instead of the month of settlement, pursuant to a related party agreement that we entered into with our affiliate. The settlement price is fixed and determinable upon the completion of transportation. As a result, the allowance oil balances at December 31, 2017 and onward no longer contain a derivative feature or result in a gain or loss related to the change in its fair value. We now settle the allowance oil at the end of each period; therefore, the balances are entirely recorded in Accounts receivable - related parties after October 1, 2017. |
