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Investments and Noncontrolling Interests (Schedule of Equity Method Investments) (Details) - USD ($)
$ in Millions

3 Months Ended

9 Months Ended

May 29, 2024

Sep. 30, 2025

Mar. 31, 2025

Sep. 30, 2025

Sep. 30, 2024

Dec. 31, 2024

Jul. 31, 2024

Schedule of Equity Method Investments

Equity method investments

$ 4,792

$ 4,792

$ 4,531

Equity Method Investments, Including Held for Sale

4,915

4,915

4,531

Investments - redemptions, repayments, return of capital and sales proceeds

143

$ 138

BANGL, LLC

Schedule of Equity Method Investments

Equity method investment, ownership percentage

45.00%

MarkWest EMG Jefferson Dry Gas Gathering Company, L.L.C.(4)

Schedule of Equity Method Investments

Investments - redemptions, repayments, return of capital and sales proceeds

$ 21

$ 21

Contribution of Property

$ 125

WPC Parent, LLC

Schedule of Equity Method Investments

Investments - redemptions, repayments, return of capital and sales proceeds

$ 134

Indirect Ownership Interest [Member] | Bakken Pipeline System [Member]

Schedule of Equity Method Investments

Equity method investment, ownership percentage

9.19%

9.19%

Crude Oil and Products Logistics

Schedule of Equity Method Investments

Equity method investments

$ 1,592

$ 1,592

1,595

Crude Oil and Products Logistics | Illinois Extension Pipeline Company, L.L.C.

Schedule of Equity Method Investments

Equity method investment, ownership percentage

35.00%

35.00%

Equity method investments

$ 219

$ 219

218

Crude Oil and Products Logistics | LOOP LLC

Schedule of Equity Method Investments

Equity method investment, ownership percentage

41.00%

41.00%

Equity method investments

$ 314

$ 314

310

Crude Oil and Products Logistics | MarEn Bakken Company LLC(1)

Schedule of Equity Method Investments

Equity method investment, ownership percentage

25.00%

25.00%

Equity method investments

^[1]

$ 508

$ 508

526

Crude Oil and Products Logistics | Other VIEs and Non-VIEs

Schedule of Equity Method Investments

Equity method investments

^[2]

551

551

541

Natural Gas and NGL Services

Schedule of Equity Method Investments

Equity method investments

$ 3,323

$ 3,323

2,936

Natural Gas and NGL Services | BANGL, LLC

Schedule of Equity Method Investments

Equity method investment, ownership percentage

100.00%

100.00%

Equity method investments

^[3]

$ 0

$ 0

281

Natural Gas and NGL Services | MarkWest EMG Jefferson Dry Gas Gathering Company, L.L.C.(4)

Schedule of Equity Method Investments

Equity method investment, ownership percentage

67.00%

67.00%

Equity method investments

$ 410

^[4]

$ 410

^[4]

329

Natural Gas and NGL Services | MarkWest Utica EMG, L.L.C.

Schedule of Equity Method Investments

Equity method investment, ownership percentage

60.00%

60.00%

Equity method investments

$ 836

$ 836

742

Natural Gas and NGL Services | Ohio Gathering Company L.L.C.

Schedule of Equity Method Investments

Equity method investment, ownership percentage

33.00%

33.00%

Equity method investments

^[5]

$ 451

$ 451

470

Natural Gas and NGL Services | Sherwood Midstream LLC

Schedule of Equity Method Investments

Equity method investment, ownership percentage

50.00%

50.00%

Equity method investments

$ 479

$ 479

488

Natural Gas and NGL Services | WPC Parent, LLC

Schedule of Equity Method Investments

Equity method investment, ownership percentage

30.00%

30.00%

Equity method investments

$ 389

$ 389

208

Natural Gas and NGL Services | Other VIEs and Non-VIEs

Schedule of Equity Method Investments

Equity method investments

^[2]

$ 758

$ 758

$ 418

Natural Gas and NGL Services | Indirect Ownership Interest [Member] | Ohio Gathering Company L.L.C.

Schedule of Equity Method Investments

Equity method investment, ownership percentage

40.00%

40.00%

[1]	The investment in MarEn Bakken Company LLC includes our 9.19 percent indirect interest in a joint venture (“Dakota Access”) that owns and operates the Dakota Access Pipeline and Energy Transfer Crude Oil Pipeline projects (collectively, the “Bakken Pipeline system”).
[2]	Included within Other are certain equity method investments that have been deemed to be VIEs, as well as $123 million in investments classified as held for sale as part of the Rockies operations divestiture discussed in Note 3.
[3]	At December 31, 2024, we owned a 45 percent interest in BANGL. On July 1, 2025, we acquired the remaining 55 percent interest in BANGL. As a result of acquiring the remaining interest, we obtained control of and now consolidate BANGL.
[4]	On March 31, 2025, MPLX contributed a 100 percent owned subsidiary with a fair value of $125 million to MarkWest EMG Jefferson Dry Gas Gathering Company, L.L.C. As a result of the transaction, MPLX received special distributions of $21 million in the first quarter of 2025 and $21 million in the third quarter of 2025, which are reflected as a return of capital on the Consolidated Statement of Cash Flows.
[5]	MPLX also holds a 40 percent indirect interest in OGC through our ownership interest in MarkWest Utica EMG, L.L.C.

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