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Fair Value Measurements (Tables) | 3 Months Ended
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Mar. 31, 2025
Fair Value Disclosures [Abstract] |
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis | The following table presents the impact on the Consolidated Balance Sheets of MPLX’s financial instruments carried at fair value on a recurring basis as of March 31, 2025 and December 31, 2024 by fair value hierarchy level.
| March 31, 2025 |  | December 31, 2024
(In millions) | Asset |  | Liability |  | Asset |  | Liability
Embedded derivatives in commodity contracts (Level 3) |  |  |  |  |  |  |
Other current assets / Other current liabilities | $ | — |  |  | $ | 9 |  |  | $ | — |  |  | $ | 10 |
Other noncurrent assets / Other long-term liabilities | — |  |  | 53 |  |  | — |  |  | 48 |
Total carrying value in Consolidated Balance Sheets | $ | — |  |  | $ | 62 |  |  | $ | — |  |  | $ | 58 |
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation | The following table is a reconciliation of the net beginning and ending balances recorded for net liabilities classified as Level 3 in the fair value hierarchy.
| Three Months Ended March 31, |  |
(In millions) | 2025 |  | 2024 |  |  |  |
Beginning balance | $ | (58) |  |  | $ | (61) |  |  |  |  |
Unrealized and realized (loss)/gain included in Net Income(1) | (7) |  |  | (12) |  |  |  |  |
Settlements | 3 |  |  | 4 |  |  |  |  |
Ending balance | $ | (62) |  |  | $ | (69) |  |  |  |  |
The amount of total loss for the period included in earnings attributable to the change in unrealized (loss)/gain relating to liabilities still held at end of period | $ | (7) |  |  | $ | (11) |  |  |  |  |
(1) (Loss)/gain on derivatives embedded in commodity contracts are recorded in Purchased product costs in the Consolidated Statements of Income.
Schedule of Carrying Values and Estimated Fair Values of Debt Instruments | The following table summarizes the fair value and carrying value of our third-party debt, excluding finance leases and unamortized debt issuance costs:
| March 31, 2025 |  | December 31, 2024
(In millions) | Fair Value |  | Carrying Value |  | Fair Value |  | Carrying Value
Outstanding debt(1) | $ | 21,120 |  |  | $ | 22,553 |  |  | $ | 19,574 |  |  | $ | 21,068 |
(1) Any amounts outstanding under the MPC Loan Agreement are not included in the table above, as the carrying value approximates fair value. This balance is reflected in Current liabilities - related parties in the Consolidated Balance Sheets.

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- Definition Tabular disclosure of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset) using recurring unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-3 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 + Details
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- Definition Tabular disclosure of information pertaining to carrying amount and estimated fair value of short-term and long-term debt instruments or arrangements, including but not limited to, identification of terms, features, and collateral requirements. + References No definition available. + Details
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- Definition Tabular disclosure of assets and liabilities, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, that are measured at fair value on a recurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 + Details
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