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Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions | 1 Months Ended | 3 Months Ended |
--- | --- | --- | ---
Dec. 31, 2020 | Jul. 31, 2020 | Mar. 31, 2025 | Dec. 31, 2024
Commitments And Contingencies [Line Items] |  |  |  |
Accrued liabilities for environmental remediation |  |  | $ 16 | $ 15
Environmental Loss Contingency, Statement of Financial Position [Extensible Enumeration] |  |  | Other current liabilities, Long-term liabilities - related parties | Other current liabilities, Long-term liabilities - related parties
Loss Contingency, Damages Sought, Value |  | $ 187 |  |
Loss Contingency, Damages Paid, Value | $ 4 |  |  |
Guarantor Obligations, Origin and Purpose |  |  | Guarantees related to indebtedness of equity method investeesDakota Access We hold a 9.19 percent indirect interest in Dakota Access, which owns and operates the Bakken Pipeline system. In 2020, the U.S. District Court for the District of Columbia (the “D.D.C.”) ordered the United States Army Corps of Engineers (“Army Corps”), which granted permits and an easement for the Bakken Pipeline system, to prepare an environmental impact statement (“EIS”) relating to an easement under Lake Oahe in North Dakota. The D.D.C. later vacated the easement. The Army Corps issued a draft EIS in September 2023 detailing various options for the easement going forward, including denying the easement, approving the easement with additional measures, rerouting the easement, or approving the easement with no changes. The Army Corps has not selected a preferred alternative, but will make a decision in its final review, after considering input from the public and other agencies. The pipeline remains operational while the Army Corps finalizes its decision which will follow the issuance of the final EIS. According to public statements from Army Corps officials, the EIS is now expected to be issued in 2025.We have entered into a Contingent Equity Contribution Agreement whereby MPLX LP, along with the other joint venture owners in the Bakken Pipeline system, has agreed to make equity contributions to the joint venture upon certain events occurring to allow the entities that own and operate the Bakken Pipeline system to satisfy their senior note payment obligations. The senior notes were issued to repay amounts owed by the pipeline companies to fund the cost of construction of the Bakken Pipeline system. If the vacatur of the easement results in a temporary shutdown of the pipeline, MPLX would have to contribute its 9.19 percent pro rata share of funds required to pay interest accruing on the notes and any portion of the principal that matures while the pipeline is shut down. MPLX also expects to contribute its 9.19 percent pro rata share of any costs to remediate any deficiencies to reinstate the easement and/or return the pipeline into operation. If the vacatur of the easement results in a permanent shutdown of the pipeline, MPLX would have to contribute its 9.19 percent pro rata share of the cost to redeem the bonds (including the one percent redemption premium required pursuant to the indenture governing the notes) and any accrued and unpaid interest. As of March 31, 2025, our maximum potential undiscounted payments under the Contingent Equity Contribution Agreement were approximately $78 million.BANGL, LLCMPLX’s maximum exposure to loss for BANGL, LLC includes a $40 million payment guaranty of an unsecured bank term loan for which BANGL, LLC is the borrower and obligor.Other guaranteesMPLX’s maximum exposure to loss for WPC Parent, LLC includes an $82 million commitment to indemnify a joint venture member for our pro rata share of any payments made under a performance guarantee for construction of a pipeline by an equity method investee. |
Financial Guarantee [Member] | Bakken Pipeline System [Member] | Guarantee of Indebtedness of Others [Member] |  |  |  |
Commitments And Contingencies [Line Items] |  |  |  |
Guarantor Obligations, Maximum Exposure, Undiscounted |  |  | $ 78 |
Financial Guarantee [Member] | BANGL, LLC | Guarantee of Indebtedness of Others [Member] |  |  |  |
Commitments And Contingencies [Line Items] |  |  |  |
Guarantor Obligations, Maximum Exposure, Undiscounted |  |  | 40 |
Performance Guarantee | WPC Parent, LLC |  |  |  |
Commitments And Contingencies [Line Items] |  |  |  |
Guarantor Obligations, Maximum Exposure, Undiscounted |  |  | $ 82 |

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