Derivatives Financial Instruments - Derivative Income Statement Location (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	$ 21	$ 4	$ (50)	$ (3)
Commodity Contract [Member] \| Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	$ 2	$ 0	$ (6)	$ 0
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Revenue from Contract with Customer, Excluding Assessed Tax - Third parties	Revenue from Contract with Customer, Excluding Assessed Tax - Third parties	Revenue from Contract with Customer, Excluding Assessed Tax - Third parties	Revenue from Contract with Customer, Excluding Assessed Tax - Third parties
Commodity Contract [Member] \| Not Designated as Hedging Instrument, Economic Hedge
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	$ 15	$ 0	$ (33)	$ 0
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Revenue from Contract with Customer, Excluding Assessed Tax - Third parties	Revenue from Contract with Customer, Excluding Assessed Tax - Third parties	Revenue from Contract with Customer, Excluding Assessed Tax - Third parties	Revenue from Contract with Customer, Excluding Assessed Tax - Third parties
Embedded Derivative [Member] \| Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	$ 4	$ 4	$ (11)	$ (3)
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Purchased product costs	Purchased product costs	Purchased product costs	Purchased product costs
Income Statement Location [Axis]: us-gaap:CostDirectMaterial \| Embedded Derivative [Member] \| Not Designated as Hedging Instrument
Derivative [Line Items]
Realized gain (loss)	$ (3)	$ (3)	$ (5)	$ (6)
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	7	7	(6)	3
Income Statement Location [Axis]: mplx:RevenueFromContractWithCustomerExcludingAssessedTaxThirdParties \| Commodity Contract [Member] \| Not Designated as Hedging Instrument
Derivative [Line Items]
Realized gain (loss)	(3)	0	(4)	0
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	5	0	(2)	0
Income Statement Location [Axis]: mplx:RevenueFromContractWithCustomerExcludingAssessedTaxThirdParties \| Commodity Contract [Member] \| Not Designated as Hedging Instrument, Economic Hedge
Derivative [Line Items]
Realized gain (loss)	(17)	0	(21)	0
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	$ 32	$ 0	$ (12)	$ 0

Amount of realized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

No definition available.

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- Definition

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4A
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4A

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482881/825-10-55-10

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- Definition

Indicates line item in statement of income or comprehensive income that includes gain (loss) from derivative.

+ References

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 5A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-5A

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-18

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 20
-Name Accounting Standards Codification
-Section 25
-Paragraph 6A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480682/815-20-25-6A

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- Definition

The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of open derivatives, commodity, or energy contracts, held at each balance sheet date, that was included in earnings for the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (b)
-SubTopic 10
-Topic 230
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-28

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