MPLX (MPLX) 10-Q 3 May 22 2022 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2022	Apr. 29, 2022
Document Information [Line Items]
Document Transition Report	false
Document Quarterly Report	true
Title of 12(b) Security	Common Units Representing Limited Partnership Interests
Entity Incorporation, State or Country Code	DE
Document Type	10-Q
Document Period End Date	Mar. 31, 2022
Amendment Flag	false
Entity File Number	001-35714
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q1
Trading Symbol	MPLX
Entity Registrant Name	MPLX LP
Entity Central Index Key	0001552000
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding		1,012,303,833
Entity Address, Address Line One	200 E. Hardin Street,
Entity Address, City or Town	Findlay,
Entity Address, State or Province	OH
Entity Address, Postal Zip Code	45840
City Area Code	419
Local Phone Number	421-2414
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
Security Exchange Name	NYSE
Entity Tax Identification Number	27-0005456

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Millions, $ in Millions		3 Months Ended
		Mar. 31, 2022	Mar. 31, 2021
Income from equity method investments		$ 99	$ 70
Other Income		(17)	1
Related Party Transaction, Other Revenues from Transactions with Related Party		27	28
Revenues		2,610	2,339
Related Party Transaction, Purchases from Related Party		319	298
Cost, Depreciation and Amortization	[1]	313	329
Taxes, Miscellaneous		34	32
Costs and Expenses		1,550	1,365
Interest And Other Financial Costs From Related Parties		4	0
Other Nonoperating Income (Expense)		20	27
Interest Expense, Debt, Excluding Amortization		198	198
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent, Total		1,060	974
Provision for income taxes		5	1
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest, Total		838	749
Less: Net income (loss) attributable to noncontrolling interest		8	9
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Total		833	748
Limited partners' interest in net income (loss) attributable to MPLX LP		793	708
Net income (loss) attributable to MPLX LP	[2]	825	739
Related Party and Third Party
General and Administrative Expense		78	86
Third Party [Member]
Operating Lease, Lease Income		91	99
Rental cost of sales
Labor and Related Expense		$ 37	$ 32
Limited Partners Common Units [Member]
Net income (loss) attributable to MPLX LP per limited partner unit:
Net Income (Loss), Per Outstanding Limited Partnership Unit, Basic, Net of Tax		$ 0.78	$ 0.68
Common - diluted (in USD per unit)		$ 0.78	$ 0.68
Weighted average limited partner units outstanding:
Common - basic (in shares)		1,015	1,037
Common - diluted (in shares)		1,015	1,037
Service [Member]
Total revenues from contracts with customers		$ 554	$ 589
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		915	872
Service, Other [Member]
Total revenues from contracts with customers		123	77
Product [Member]
Total revenues from contracts with customers		497	282
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		45	42
Oil and Gas, Refining and Marketing [Member]
Cost of Goods and Services Sold		287	273
Natural Gas, Midstream [Member]
Cost of Goods and Services Sold		467	276
Series A Preferred Stock [Member] | Preferred Partner [Member]
Dividends, Preferred Stock		21	20
Net income (loss) attributable to MPLX LP	[2]	23	20
Series B Preferred Stock [Member] | Preferred Partner [Member]
Dividends, Preferred Stock		11	11
Net income (loss) attributable to MPLX LP	[2]	11	11
Affiliated Entity
Sales-type Lease, Revenue		111	37
Operating Lease, Lease Income, Related Party [Line Items]		165	242
Affiliated Entity | Rental cost of sales - related parties
Labor and Related Expense		15	39
Affiliated Entity | Service [Member]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		915	872
Affiliated Entity | Product [Member]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		$ 45	$ 42
[1]	Depreciation and amortization attributable to L&S was $130 million and $147 million for the three months ended March 31, 2022 and March 31, 2021, respectively. Depreciation and amortization attributable to G&P was $183 million and $182 million for the three months ended March 31, 2022 and March 31, 2021, respectively.
[2]	Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

Consolidated Statements of In_2

Consolidated Statements of Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Income Statement [Abstract]
Interest Costs Capitalized	$ 2	$ 5

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Statement of Comprehensive Income [Abstract]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 833	$ 748
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest, Total	842	746
Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest [Abstract]
Less: Net income (loss) attributable to noncontrolling interest	8	9
Comprehensive Income (Loss), Net of Tax, Attributable to Parent, Total	834	737
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Statement of Comprehensive Income [Abstract]
Other Comprehensive Income (Loss), Net of Tax	9	(2)
Other Comprehensive Income (Loss), Net of Tax	$ 9	$ (2)

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) shares in Millions, $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Assets
Cash and cash equivalents	$ 42	$ 13
Receivables, net	741	654
Inventories	149	142
Total current assets	1,798	1,507
Equity method investments	4,079	3,981
Property, plant and equipment, net	19,912	20,042
Intangibles, net	800	831
Goodwill	7,657	7,657
Other noncurrent assets	50	60
Total assets	35,727	35,507
Liabilities
Accounts Payable, Current	214	172
Accrued Liabilities, Current	396	363
Accrued Property Plant and Equipment Current	91	97
Long-term Debt and Lease Obligation, Current	999	499
Interest Payable, Current	192	202
Operating Lease, Liability, Current	47	59
Other current liabilities	232	176
Total current liabilities	2,858	3,348
Long-term deferred revenue	405	383
Long-term debt	18,757	18,072
Deferred Income Taxes and Other Tax Liabilities, Noncurrent	14	10
Operating Lease, Liability, Noncurrent	228	205
Deferred credits and other liabilities	159	170
Total liabilities	22,726	22,490
Commitments and contingencies (see Note 14)
Equity
Total MPLX LP partners’ capital	11,796	11,811
Noncontrolling interests	240	241
Total equity	12,036	12,052
Total liabilities, preferred units and equity	35,727	35,507
Third Party [Member]
Assets
Other current assets	53	54
Operating Lease, Right-of-Use Asset	280	268
Affiliated Entity
Assets
Current Assets, Related Parties	813	644
Other current assets	3	3
Operating Lease, Right-of-Use Asset	229	229
Due from Related Parties, Noncurrent	1,151	1,161
Liabilities
Due to Related Parties, Current	687	1,780
Liabilities, Related Parties, Noncurrent	$ 305	$ 302
Series B Preferred Stock [Member]
Liabilities
Preferred Units, Issued	0.6	0.6
Preferred Units, Outstanding	0.6	0.6
Equity
Preferred Units, Preferred Partners' Capital Accounts	$ 601	$ 611
Limited Partners Common Units [Member] | Public [Member]
Liabilities
Units issued	366	369
Equity
Limited Partners' Capital Account	$ 8,505	$ 8,579
Units Outstanding	366	369
Limited Partners Common Units [Member] | Marathon Petroleum Corporation [Member]
Liabilities
Units issued	647	647
Equity
Limited Partners' Capital Account	$ 2,698	$ 2,638
Units Outstanding	647	647
Series A Convertible Preferred Units
Liabilities
Preferred Units, Issued	30	30
Preferred Units, Outstanding	30	30
Series A Preferred Stock [Member]
Liabilities
Series A preferred units (30 million and 30 million units issued and outstanding)	$ 965	$ 965
LOOP and Explorer
Equity
Accumulated other comprehensive loss	$ (8)	$ (17)

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - Limited Partners Common Units [Member] - shares shares in Millions	Mar. 31, 2022	Dec. 31, 2021
Public [Member]
Units issued	366	369
Units Outstanding	366	369
Marathon Petroleum Corporation [Member]
Units issued	647	647
Units Outstanding	647	647

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2022	Mar. 31, 2021
Operating activities:
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		$ 833	$ 748
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of deferred financing costs		18	17
Cost, Depreciation and Amortization	[1]	313	329
Deferred income taxes		4	0
Income from equity method investments		(99)	(70)
Proceeds from Equity Method Investment, Distribution		120	119
Increase (Decrease) in Derivative Assets and Liabilities		(9)	3
Changes in:
Current receivables		(87)	(67)
Inventories		(7)	(11)
Current accounts payable and accrued liabilities		73	26
Current assets/current liabilities - related parties		(112)	(8)
Increase (Decrease) in Other Operating Assets and Liabilities, Net		(1)	(1)
Deferred revenue		16	24
All other, net		45	15
Net cash provided by operating activities		1,125	1,124
Net Cash Provided by (Used in) Investing Activities [Abstract]
Additions to property, plant and equipment		(169)	(126)
Disposal of assets		3	70
Payments to Acquire Equity Method Investments		(110)	(35)
Payments for (Proceeds from) Other Investing Activities		0	1
Net cash used in investing activities		(276)	(90)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Long-term debt - borrowings		2,385	1,910
Long-term debt - repayments		(1,201)	(2,020)
Payments of Debt Issuance Costs		16	0
Payments for Repurchase of Common Stock		(100)	(155)
Distributions to noncontrolling interests		(9)	(10)
Distributions to unitholders and general partner		(716)	(713)
Proceeds from Contributions from Parent		10	7
All other, net		(4)	(3)
Net cash used in financing activities		(820)	(1,025)
Net increase in cash, cash equivalents and restricted cash		29	9
Cash, cash equivalents and restricted cash at beginning of period		13	15
Cash, cash equivalents and restricted cash at end of period		42	24
Loss on disposal of assets		18	0
Related Party Revolving Credit Agreement [Member] | MPC Investment [Member]
Net Cash Provided by (Used in) Financing Activities [Abstract]
Related party debt - borrowings		1,849	2,241
Repayments of Related Party Debt		(2,976)	(2,241)
Series A Preferred Stock [Member] | Preferred Partner [Member]
Net Cash Provided by (Used in) Financing Activities [Abstract]
Distributions to preferred unitholders		(21)	(20)
Series B Preferred Stock [Member] | Preferred Partner [Member]
Net Cash Provided by (Used in) Financing Activities [Abstract]
Distributions to preferred unitholders		$ (21)	$ (21)
[1]	Depreciation and amortization attributable to L&S was $130 million and $147 million for the three months ended March 31, 2022 and March 31, 2021, respectively. Depreciation and amortization attributable to G&P was $183 million and $182 million for the three months ended March 31, 2022 and March 31, 2021, respectively.

Consolidated Statements of Equi

Consolidated Statements of Equity - USD ($) $ in Millions	Total	LOOP and Explorer	Series B Preferred Stock [Member]	Series A Preferred Stock [Member]	Public [Member]Limited Partners Common Units [Member]	Marathon Petroleum Corporation [Member]Limited Partners Common Units [Member]	AOCI Attributable to Parent [Member]	Noncontrolling Interest [Member]
Preferred Units, Preferred Partners' Capital Accounts			$ 611
Limited Partners' Capital Account					$ 9,384	$ 2,792
Noncontrolling interests	$ 245
Accumulated other comprehensive loss		$ (15)
Series A preferred units (30 million and 30 million units issued and outstanding)				$ 968
Beginning Balance at Dec. 31, 2020	13,017
Distributions to:	729		11		266	443	$ 0	$ 9
Stock Repurchased and Retired During Period, Value	(155)		0	0	(155)	0	0	0
Partners' Capital Account, Distributions	(745)		(21)	(20)	(269)	(445)	0	(10)
Other	(3)		0		0	(1)	(2)	0
Ending Balance at Mar. 31, 2021	12,850
Temporary Equity, Net Income				20
Partners' Capital Account, Contributions	7		0	0	0	7	0	0
Temporary Equity, Other Changes				0
Preferred Units, Preferred Partners' Capital Accounts			601
Limited Partners' Capital Account					9,226	2,796
Noncontrolling interests	244
Accumulated other comprehensive loss		(17)
Series A preferred units (30 million and 30 million units issued and outstanding)				968
Preferred Units, Preferred Partners' Capital Accounts			611
Limited Partners' Capital Account					8,579	2,638
Noncontrolling interests	241
Accumulated other comprehensive loss		(17)
Series A preferred units (30 million and 30 million units issued and outstanding)				965
Beginning Balance at Dec. 31, 2021	12,052
Distributions to:	812		11		287	506	0	8
Stock Repurchased and Retired During Period, Value	(100)		0	0	(100)	0	0	0
Partners' Capital Account, Distributions	(746)		(21)	(21)	(260)	(456)	0	(9)
Other	8		0		(1)	0	9	0
Ending Balance at Mar. 31, 2022	12,036
Temporary Equity, Net Income				21
Partners' Capital Account, Contributions	10		0	0	0	10	$ 0	$ 0
Temporary Equity, Other Changes				0
Preferred Units, Preferred Partners' Capital Accounts			$ 601
Limited Partners' Capital Account					$ 8,505	$ 2,698
Noncontrolling interests	$ 240
Accumulated other comprehensive loss		$ (8)
Series A preferred units (30 million and 30 million units issued and outstanding)				$ 965

Description of the Business and

Description of the Business and Basis of Presentation	3 Months Ended
	Mar. 31, 2022
Accounting Policies [Abstract]
Business Description and Basis of Presentation [Text Block]	Description of the Business and Basis of Presentation Description of the Business MPLX LP is a diversified, large-cap master limited partnership formed by Marathon Petroleum Corporation that owns and operates midstream energy infrastructure and logistics assets, and provides fuels distribution services. References in this report to “MPLX LP,” “MPLX,” “the Partnership,” “we,” “ours,” “us,” or like terms refer to MPLX LP and its subsidiaries. References to “MPC” refer collectively to Marathon Petroleum Corporation as our sponsor and its subsidiaries, other than the Partnership. We are engaged in the gathering, transportation, storage and distribution of crude oil, refined products and other hydrocarbon-based products; the gathering, processing and transportation of natural gas; and the gathering, transportation, fractionation, storage and marketing of NGLs. MPLX’s principal executive office is located in Findlay, Ohio. MPLX’s business consists of two segments based on the nature of services it offers: Logistics and Storage (“L&S”), which relates primarily to crude oil, refined products and other hydrocarbon-based products; and Gathering and Processing (“G&P”), which relates primarily to natural gas and NGLs. See Note 7 for additional information regarding the operations and results of these segments. Basis of Presentation The accompanying interim consolidated financial statements are unaudited; however, in the opinion of MPLX’s management, these statements reflect all adjustments necessary for a fair statement of the results for the periods reported. All such adjustments are of a normal, recurring nature unless otherwise disclosed. These interim consolidated financial statements, including the notes, have been prepared in accordance with the rules and regulations of the SEC applicable to interim period financial statements and do not include all of the information and disclosures required by GAAP for complete financial statements. Certain information derived from our audited annual financial statements, prepared in accordance with GAAP, has been condensed or omitted from these interim financial statements. These interim consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in our Annual Report on Form 10-K for the year ended December 31, 2021. The results of operations for the three months ended March 31, 2022 are not necessarily indicative of the results to be expected for the full year. MPLX’s consolidated financial statements include all majority-owned and controlled subsidiaries. For non-wholly owned consolidated subsidiaries, the interests owned by third parties have been recorded as “Noncontrolling interests” on the accompanying Consolidated Balance Sheets. Intercompany investments, accounts and transactions have been eliminated. MPLX’s investments in which MPLX exercises significant influence but does not control and does not have a controlling financial interest are accounted for using the equity method. MPLX’s investments in VIEs in which MPLX exercises significant influence but does not control and is not the primary beneficiary are also accounted for using the equity method.

Accounting Standards Accounting

Accounting Standards Accounting Standards	3 Months Ended
	Mar. 31, 2022
Accounting Changes and Error Corrections [Abstract]
Accounting Standards Update and Change in Accounting Principle [Text Block]	Accounting Standards Recently Adopted ASU 2021-10, Government Assistance (Topic 832): Disclosures by Business Entities about Government Assistance In November 2021, the FASB issued guidance requiring disclosures for certain types of government assistance that have been accounted for by analogy to grant or contribution models. Disclosures will include information about the type of transactions, accounting and the impact on financial statements. MPLX prospectively adopted this standard in the first quarter of 2022. The adoption of this standard did not have a material impact on our financial statements or disclosures.

Investments and Noncontrolling

Investments and Noncontrolling Interest	3 Months Ended
	Mar. 31, 2022
Equity Method Investments and Joint Ventures [Abstract]
Investments and Noncontrolling Interests [Text Block]	Investments and Noncontrolling Interests The following table presents MPLX’s equity method investments at the dates indicated: Ownership as of Carrying value at March 31, March 31, December 31, (In millions, except ownership percentages) 2022 2022 2021 L&S MarEn Bakken Company LLC (1) 25% $ 502 $ 449 Illinois Extension Pipeline Company, L.L.C. 35% 249 243 LOOP LLC 41% 274 265 Andeavor Logistics Rio Pipeline LLC (2) 67% 181 183 Minnesota Pipe Line Company, LLC 17% 182 183 Whistler Pipeline LLC (2) 38% 166 155 Explorer Pipeline Company 25% 65 66 W2W Holdings LLC (2) 50% 56 58 Other (2) 125 116 Total L&S 1,800 1,718 G&P MarkWest Utica EMG, L.L.C. (2) 57% 681 680 Sherwood Midstream LLC (2) 50% 539 544 MarkWest EMG Jefferson Dry Gas Gathering Company, L.L.C. (2) 67% 336 332 MarkWest Torñado GP, L.L.C. (2) 60% 266 246 Rendezvous Gas Services, L.L.C. (2) 78% 145 147 Sherwood Midstream Holdings LLC (2) 51% 133 136 Centrahoma Processing LLC 40% 133 133 Other (2) 46 45 Total G&P 2,279 2,263 Total $ 4,079 $ 3,981 (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 referred to as the Bakken Pipeline system or DAPL. (2) Investments deemed to be VIEs. Some investments included within “Other” have also been deemed to be VIEs. For those entities that have been deemed to be VIEs, neither MPLX nor any of its subsidiaries have been deemed to be the primary beneficiary due to voting rights on significant matters. While we have the ability to exercise influence through participation in the management committees which make all significant decisions, we have equal influence over each committee as a joint interest partner and all significant decisions require the consent of the other investors without regard to economic interest; as such, we have determined that these entities should not be consolidated and apply the equity method of accounting with respect to our investments in each entity. Sherwood Midstream LLC (“Sherwood Midstream”) has been deemed the primary beneficiary of Sherwood Midstream Holdings LLC (“Sherwood Midstream Holdings”) due to its controlling financial interest through its authority to manage the joint venture. As a result, Sherwood Midstream consolidates Sherwood Midstream Holdings. Therefore, MPLX also reports its portion of Sherwood Midstream Holdings’ net assets as a component of its investment in Sherwood Midstream. As of March 31, 2022, MPLX has a 24.55 percent indirect ownership interest in Sherwood Midstream Holdings through Sherwood Midstream. MPLX’s maximum exposure to loss as a result of its involvement with equity method investments includes its equity investment, any additional capital contribution commitments and any operating expenses incurred by the subsidiary operator in excess of its compensation received for the performance of the operating services. MPLX did not provide any financial support to equity method investments that it was not contractually obligated to provide during the three months ended March 31, 2022. Summarized financial information for MPLX’s equity method investments for the three months ended March 31, 2022 and 2021 is as follows: Three Months Ended March 31, 2022 (In millions) VIEs Non-VIEs Total Revenues and other income $ 249 $ 308 $ 557 Costs and expenses 137 129 266 Income from operations 112 179 291 Net income 103 166 269 Income from equity method investments $ 55 $ 44 $ 99 Three Months Ended March 31, 2021 (In millions) VIEs Non-VIEs Total Revenues and other income $ 163 $ 284 $ 447 Costs and expenses 107 131 238 Income from operations 56 153 209 Net income 64 140 204 Income from equity method investments $ 39 $ 31 $ 70 Summarized balance sheet information for MPLX’s equity method investments as of March 31, 2022 and December 31, 2021 is as follows: March 31, 2022 (In millions) VIEs Non-VIEs Total Current assets $ 386 $ 370 $ 756 Noncurrent assets 7,482 4,875 12,357 Current liabilities 773 259 1,032 Noncurrent liabilities $ 1,929 $ 789 $ 2,718 December 31, 2021 (In millions) VIEs Non-VIEs Total Current assets $ 335 $ 411 $ 746 Noncurrent assets 7,439 4,895 12,334 Current liabilities 217 310 527 Noncurrent liabilities $ 2,461 $ 788 $ 3,249

Related Party Agreements and Tr

Related Party Agreements and Transactions	3 Months Ended
	Mar. 31, 2022
Related Party Transactions [Abstract]
Related Party Agreements and Transactions	Related Party Agreements and Transactions MPLX engages in transactions with both MPC and certain of its equity method investments as part of its normal business; however, transactions with MPC make up the majority of MPLX’s related party transactions. Transactions with related parties are further described below. MPLX has various long-term, fee-based commercial agreements with MPC. Under these agreements, MPLX provides transportation, gathering, terminal, fuels distribution, marketing, storage, management, operational and other services to MPC. MPC has committed to provide MPLX with minimum quarterly throughput volumes on crude oil and refined products, other fees for storage capacity, operating and management fees, as well as reimbursements for certain direct and indirect costs. MPC has also committed to provide a fixed fee for 100 percent of available capacity for boats, barges and third-party chartered equipment under the marine transportation service agreement. MPLX also has a keep-whole commodity agreement with MPC under which MPC pays us a processing fee for NGLs related to keep-whole agreements and delivers shrink gas to the producers on our behalf. We pay MPC a marketing fee in exchange for assuming the commodity risk. Additionally, MPLX has obligations to MPC for services provided to MPLX by MPC under omnibus and employee services-type agreements as well as other agreements. Related Party Loan MPLX is party to a loan agreement with MPC Investment LLC (“MPC Investment”) (the “MPC Loan Agreement”). Under the terms of the agreement, MPC Investment extends loans to MPLX on a revolving basis as requested by MPLX and as agreed to by MPC Investment. The borrowing capacity of the MPC Loan Agreement is $1.5 billion aggregate principal amount of all loans outstanding at any one time. The loan agreement is scheduled to expire, and borrowings under the loan agreement are scheduled to mature and become due and payable, on July 31, 2024, provided that MPC Investment may demand payment of all or any portion of the outstanding principal amount of the loan, together with all accrued and unpaid interest and other amounts (if any), at any time prior to maturity. Borrowings under the MPC Loan Agreement bear interest at LIBOR plus 1.25 percent or such lower rate as would be applicable to such loans under the MPLX Credit Agreement as discussed in Note 11. Activity on the MPC Loan Agreement was as follows: Three Months Ended March 31, (In millions) 2022 2021 Borrowings $ 1,849 $ 2,241 Average interest rate of borrowings 1.400 % 1.371 % Repayments $ 2,976 $ 2,241 Outstanding balance at end of period $ 323 $ — Related Party Revenue Related party sales to MPC primarily consist of crude oil and refined products pipeline and trucking transportation services based on tariff or contracted rates; storage, terminal and fuels distribution services based on contracted rates; and marine transportation services. Related party sales to MPC also consist of revenue related to volume deficiency credits. MPLX also has operating agreements with MPC under which it receives a fee for operating MPC’s retained pipeline assets and a fixed annual fee for providing oversight and management services required to run the marine business. MPLX also receives management fee revenue for engineering, construction and administrative services for operating certain of its equity method investments. These agreements are classified as “Other income - related parties” on the Consolidated Statements of Income. Certain product sales to MPC net to zero within the consolidated financial statements as the transactions are recorded net due to the terms of the agreements under which such product was sold. For the three months ended March 31, 2022 and March 31, 2021, these sales totaled $293 million and $168 million, respectively. Related Party Expenses MPC charges MPLX for executive management services and certain general and administrative services to MPLX under the terms of our omnibus agreements (“Omnibus charges”). Omnibus charges included in “Rental cost of sales - related parties” primarily relate to services that support MPLX’s rental operations and maintenance of assets available for rent, as well as compensation expenses. Omnibus charges included in “Purchases - related parties” primarily relate to services that support MPLX’s operations and maintenance activities, as well as compensation expenses. Omnibus charges included in “General and administrative expenses” primarily relate to services that support MPLX’s executive management, accounting and human resources activities. MPLX also obtains employee services from MPC under employee services agreements (“ESA charges”). ESA charges for personnel directly involved in or supporting operations and maintenance activities related to rental services are classified as “Rental cost of sales - related parties.” ESA charges for personnel directly involved in or supporting operations and maintenance activities related to other services are classified as “Purchases - related parties.” ESA charges for personnel involved in executive management, accounting and human resources activities are classified as “General and administrative expenses.” In addition to these agreements, MPLX purchases products from MPC, makes payments to MPC in its capacity as general contractor to MPLX, and has certain lease agreements with MPC. For the three months ended March 31, 2022 and March 31, 2021, “General and administrative expenses” incurred from MPC totaled $55 million and $57 million, respectively. Some charges incurred under the omnibus and ESA agreements are related to engineering services and are associated with assets under construction. These charges are added to “Property, plant and equipment, net” on the Consolidated Balance Sheets. For the three months ended March 31, 2022 and March 31, 2021, these charges totaled $19 million and $12 million, respectively. Related Party Assets and Liabilities Assets and liabilities with related parties appearing on the Consolidated Balance Sheets are detailed in the table below. This table identifies the various components of related party assets and liabilities, including those associated with leases and deferred revenue on minimum volume commitments. If MPC fails to meet its minimum committed volumes, MPC will pay MPLX a deficiency payment based on the terms of the agreement. The deficiency amounts received under these agreements (excluding payments received under agreements classified as sales-type leases) are recorded as “Current liabilities - related parties.” In many cases, MPC may then apply the amount of any such deficiency payments as a credit for volumes in excess of its minimum volume commitment in future periods under the terms of the applicable agreements. MPLX recognizes related party revenues for the deficiency payments when credits are used for volumes in excess of minimum quarterly volume commitments, where it is probable the customer will not use the credit in future periods or upon the expiration of the credits. The use or expiration of the credits is a decrease in “Current liabilities - related parties.” Deficiency payments under agreements that have been classified as sales-type leases are recorded as a reduction against the corresponding lease receivable. In addition, capital projects MPLX undertakes at the request of MPC are reimbursed in cash and recognized as revenue over the remaining term of the applicable agreements or in some cases, as a contribution from MPC. (In millions) March 31, 2022 December 31, 2021 Current assets - related parties Receivables $ 707 $ 555 Prepaid 17 4 Other 3 3 Lease receivables 86 82 Total 813 644 Noncurrent assets - related parties Long-term receivables 30 31 Right of use assets 229 229 Long-term lease receivables 828 854 Unguaranteed residual asset 64 47 Total 1,151 1,161 Current liabilities - related parties MPC loan agreement and other payables (1) 606 1,702 Operating lease liabilities 1 1 Deferred revenue - Minimum volume deficiencies 38 35 Deferred revenue - Project reimbursements 42 42 Total 687 1,780 Long-term liabilities - related parties Long-term operating lease liabilities 228 228 Long-term deferred revenue - Project reimbursements 77 74 Total $ 305 $ 302 (1) Includes $323 million as of March 31, 2022 and $1,450 million as of December 31, 2021 related to outstanding borrowings on the intercompany loan with MPC, which are included in “Current liabilities - related parties” on the Consolidated Balance Sheets.

Equity

Equity	3 Months Ended
	Mar. 31, 2022
Equity [Abstract]
Equity	Equity The changes in the number of common units during the three months ended March 31, 2022 are summarized below: (In units) Common Balance at December 31, 2021 1,016,178,378 Unit-based compensation awards 148,951 Units redeemed in unit repurchase program (3,119,522) Balance at March 31, 2022 1,013,207,807 Unit Repurchase Program On November 2, 2020, MPLX announced the board authorization of a unit repurchase program for the repurchase of up to $1 billion of MPLX’s outstanding common units held by the public. MPLX may utilize various methods to effect the repurchases, which could include open market repurchases, negotiated block transactions, tender offers, accelerated unit repurchases or open market solicitations for units, some of which may be effected through Rule 10b5-1 plans. The timing and amount of repurchases will depend upon several factors, including market and business conditions, and repurchases may be initiated, suspended or discontinued at any time. The repurchase authorization has no expiration date. During the three months ended March 31, 2022, we repurchased 3,119,522 common units at an average cost per unit of $32.06 per unit and paid $100 million of cash. As of March 31, 2022, we had $237 million remaining under our repurchase authorization. Series B Preferred Units MPLX has 600,000 outstanding units of 6.875 percent Fixed-to-Floating Rate Cumulative Redeemable Perpetual Preferred Units representing limited partner interests of MPLX with a price to the public of $1,000 per unit (the “Series B preferred units”). The Series B preferred units are pari passu with the Series A preferred units with respect to distribution rights and rights upon liquidation. Series B preferred unitholders are entitled to receive a fixed distribution of $68.75 per unit, per annum, payable semi-annually in arrears on the 15th day, or the first business day thereafter, of February and August of each year up to and including February 15, 2023. After February 15, 2023, the holders of Series B preferred units are entitled to receive cumulative, quarterly distributions payable in arrears on the 15th day of February, May, August and November of each year, or the first business day thereafter, based on a floating annual rate equal to the three-month LIBOR plus 4.652 percent, in each case assuming a distribution is declared by the Board of Directors. MPLX has the right to redeem some or all of the Series B preferred units, at any time, on or after February 15, 2023 at the Series B preferred unit redemption price of $1,000 per unit, plus any accumulated and unpaid distributions up to the redemption date. Cash distributions On April 26, 2022, MPLX declared a cash distribution for the first quarter of 2022, totaling $713 million, or $0.7050 per common unit. This distribution will be paid on May 13, 2022 to common unitholders of record on May 6, 2022. This rate will also be received by Series A preferred unitholders. Quarterly distributions for 2022 and 2021 are summarized below: (Per common unit) 2022 2021 March 31, $ 0.7050 $ 0.6875 In accordance with the distribution rights discussed above, MPLX made a cash distribution totaling $21 million to Series B unitholders on February 15, 2022. The allocation of total quarterly cash distributions to limited and preferred unitholders is as follows for the three months ended March 31, 2022 and 2021. Distributions, although earned, are not accrued until declared. MPLX’s distributions are declared subsequent to quarter end; therefore, the following table represents total cash distributions applicable to the period in which the distributions were earned. Three Months Ended March 31, (In millions) 2022 2021 Common and preferred unit distributions: Common unitholders, includes common units of general partner $ 713 $ 707 Series A preferred unit distributions 21 20 Series B preferred unit distributions 11 11 Total cash distributions declared $ 745 $ 738

Net Income Per Limited Partner

Net Income Per Limited Partner Unit	3 Months Ended
	Mar. 31, 2022
Earnings Per Share [Abstract]
Earnings Per Share [Text Block]	Net Income/(Loss) Per Limited Partner Unit Net income/(loss) per unit applicable to common units is computed by dividing net income attributable to MPLX LP less income allocated to participating securities by the weighted average number of common units outstanding. During the three months ended March 31, 2022 and 2021, MPLX had participating securities consisting of common units, certain equity-based compensation awards, Series A preferred units and Series B preferred units and had dilutive potential common units consisting of certain equity-based compensation awards. Potential common units omitted from the diluted earnings per unit calculation for the three months ended March 31, 2022 and 2021 were less than 1 million. Three Months Ended March 31, (In millions) 2022 2021 Net income attributable to MPLX LP $ 825 $ 739 Less: Distributions declared on Series A preferred units 21 20 Distributions declared on Series B preferred units 11 11 Limited partners’ distributions declared on MPLX common units (including common units of general partner) 713 707 Undistributed net gain attributable to MPLX LP $ 80 $ 1 Three Months Ended March 31, 2022 (In millions, except per unit data) Limited Partners’ Series A Preferred Units Series B Preferred Units Total Basic and diluted net income attributable to MPLX LP per unit Net income attributable to MPLX LP: Distributions declared $ 713 $ 21 $ 11 $ 745 Undistributed net gain attributable to MPLX LP 78 2 — 80 Net income attributable to MPLX LP (1) $ 791 $ 23 $ 11 $ 825 Weighted average units outstanding: Basic 1,015 Diluted 1,015 Net income attributable to MPLX LP per limited partner unit: Basic $ 0.78 Diluted $ 0.78 (1) Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period. Three Months Ended March 31, 2021 (In millions, except per unit data) Limited Partners’ Series A Preferred Units Series B Preferred Units Total Basic and diluted net income attributable to MPLX LP per unit Net income attributable to MPLX LP: Distributions declared $ 707 $ 20 $ 11 $ 738 Undistributed net gain attributable to MPLX LP 1 — — 1 Net income attributable to MPLX LP (1) $ 708 $ 20 $ 11 $ 739 Weighted average units outstanding: Basic 1,037 Diluted 1,037 Net income attributable to MPLX LP per limited partner unit: Basic $ 0.68 Diluted $ 0.68 (1) Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 2022
Segment Reporting [Abstract]
Segment Reporting Disclosure [Text Block]	Segment Information MPLX’s chief operating decision maker is the chief executive officer (“CEO”) of its general partner. The CEO reviews MPLX’s discrete financial information, makes operating decisions, assesses financial performance and allocates resources on a type of service basis. MPLX has two reportable segments: L&S and G&P. Each of these segments is organized and managed based upon the nature of the products and services it offers. • L&S – transports, gathers, stores and distributes crude oil, refined products, and other hydrocarbon-based products. Also includes the operation of refining logistics, fuels distribution and inland marine businesses, terminals, rail facilities, and storage caverns. • G&P – gathers, processes and transports natural gas; and gathers, transports, fractionates, stores and markets NGLs. Our CEO evaluates the performance of our segments using Segment Adjusted EBITDA. Amounts included in net income and excluded from Segment Adjusted EBITDA include: (i) depreciation and amortization; (ii) interest and other financial costs; (iii) impairment expense; (iv) income/(loss) from equity method investments; (v) distributions and adjustments related to equity method investments; (vi) noncontrolling interests; and (vii) other adjustments as deemed necessary. These items are either: (i) believed to be non-recurring in nature; (ii) not believed to be allocable or controlled by the segment; or (iii) are not tied to the operational performance of the segment. The tables below present information about revenues and other income, Segment Adjusted EBITDA, restructuring expenses, capital expenditures and investments in unconsolidated affiliates for our reportable segments: Three Months Ended March 31, (In millions) 2022 2021 L&S Service revenue $ 983 $ 953 Rental income 175 249 Product related revenue 4 4 Sales-type lease revenue 111 37 Income from equity method investments 52 36 Other income 12 15 Total segment revenues and other income (1) 1,337 1,294 Segment Adjusted EBITDA (2) 904 896 Capital expenditures 77 59 Investments in unconsolidated affiliates 68 9 G&P Service revenue 486 508 Rental income 81 92 Product related revenue 661 397 Income from equity method investments 47 34 Other income/(loss) (2) 14 Total segment revenues and other income (1) 1,273 1,045 Segment Adjusted EBITDA (2) 489 456 Capital expenditures 95 30 Investments in unconsolidated affiliates $ 42 $ 26 (1) Within the total segment revenues and other income amounts presented above, third party revenues for the L&S segment were $135 million and $129 million for the three months ended March 31, 2022 and March 31, 2021, respectively. Third party revenues for the G&P segment were $1,212 million and $989 million for the three months ended March 31, 2022 and March 31, 2021, respectively. (2) See below for the reconciliation from Segment Adjusted EBITDA to “Net income.” The table below provides a reconciliation between “Net income” and Segment Adjusted EBITDA. Three Months Ended March 31, (In millions) 2022 2021 Reconciliation to Net income: L&S Segment Adjusted EBITDA $ 904 $ 896 G&P Segment Adjusted EBITDA 489 456 Total reportable segments 1,393 1,352 Depreciation and amortization (1) (313) (329) Interest and other financial costs (222) (225) Income from equity method investments 99 70 Distributions/adjustments related to equity method investments (132) (121) Other (1) (9) Adjusted EBITDA attributable to noncontrolling interests 9 10 Net income $ 833 $ 748 (1) Depreciation and amortization attributable to L&S was $130 million and $147 million for the three months ended March 31, 2022 and March 31, 2021, respectively. Depreciation and amortization attributable to G&P was $183 million and $182 million for the three months ended March 31, 2022 and March 31, 2021, respectively.

Property, Plant and Equipment

Property, Plant and Equipment	3 Months Ended
	Mar. 31, 2022
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property, Plant and Equipment Property, plant and equipment with associated accumulated depreciation is shown below: March 31, 2022 December 31, 2021 (In millions) Gross PP&E Accumulated Depreciation Net PP&E Gross PP&E Accumulated Depreciation Net PP&E L&S $ 12,438 $ 3,347 $ 9,091 $ 12,371 $ 3,227 $ 9,144 G&P 14,253 3,432 10,821 14,175 3,277 10,898 Total $ 26,691 $ 6,779 $ 19,912 $ 26,546 $ 6,504 $ 20,042

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2022
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Fair Values – Recurring Fair value measurements and disclosures relate primarily to MPLX’s derivative positions as discussed in Note 10. Level 3 instruments relate to an embedded derivative liability for a natural gas purchase commitment embedded in a keep-whole processing agreement. The fair value calculation for these Level 3 instruments used significant unobservable inputs including: (1) NGL prices interpolated and extrapolated due to inactive markets ranging from $0.73 to $2.38 per gallon with a weighted average of $0.97 per gallon and (2) the probability of renewal of 100 percent for the five Changes in Level 3 Fair Value Measurements The following table is a reconciliation of the net beginning and ending balances recorded for net assets and liabilities classified as Level 3 in the fair value hierarchy. Three Months Ended March 31, 2022 2021 (In millions) Embedded Derivatives in Commodity Contracts (net) Embedded Derivatives in Commodity Contracts (net) Fair value at beginning of period $ (108) $ (63) Total gain/(loss) (realized and unrealized) included in earnings (1) 4 (6) Settlements 5 3 Fair value at end of period (99) (66) The amount of total gain/(loss) for the period included in earnings attributable to the change in unrealized gain/(loss) relating to liabilities still held at end of period $ 5 $ (5) (1) Gain/(loss) on derivatives embedded in commodity contracts are recorded in “Purchased product costs” on the Consolidated Statements of Income. Fair Values – Reported MPLX’s primary financial instruments are cash and cash equivalents, receivables, receivables from related parties, lease receivables from related parties, accounts payable, payables to related parties and debt. MPLX’s fair value assessment incorporates a variety of considerations, including (1) the duration of the instruments, (2) MPC’s investment-grade credit rating and (3) the historical incurrence of and expected future insignificance of bad debt expense, which includes an evaluation of counterparty credit risk. MPLX believes the carrying values of its current assets and liabilities approximate fair value. The recorded value of the amounts outstanding under the bank revolving credit facility, if any, approximates fair value due to the variable interest rate that approximate current market rates. Derivative instruments are recorded at fair value, based on available market information (see Note 10). The fair value of MPLX’s debt is estimated based on recent market non-binding indicative quotes. The debt fair values are considered Level 3 measurements. 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, 2022 December 31, 2021 (In millions) Fair Value Carrying Value Fair Value Carrying Value Outstanding debt (1) $ 20,392 $ 19,864 $ 20,779 $ 18,664 (1) 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” on the Consolidated Balance Sheets.

Derivative Financial Instrument

Derivative Financial Instruments	3 Months Ended
	Mar. 31, 2022
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments and Hedging Activities Disclosure [Text Block]	Derivative Financial Instruments As of March 31, 2022, MPLX had no commodity contracts beyond the embedded derivative discussed below. Embedded Derivative - MPLX has a natural gas purchase commitment embedded in a keep-whole processing agreement with a producer customer in the Southern Appalachian region expiring in December 2027. The customer has the unilateral option to extend the agreement for one five Certain derivative positions are subject to master netting agreements, therefore, MPLX has elected to offset derivative assets and liabilities that are legally permissible to be offset. As of March 31, 2022 and December 31, 2021, there were no derivative assets or liabilities that were offset on the Consolidated Balance Sheets. The impact of MPLX’s derivative instruments on its Consolidated Balance Sheets is summarized below: (In millions) March 31, 2022 December 31, 2021 Derivative contracts not designated as hedging instruments and their balance sheet location Asset Liability Asset Liability Commodity contracts (1) Other current assets / Other current liabilities $ — $ (16) $ — $ (15) Other noncurrent assets / Deferred credits and other liabilities — (83) — (93) Total $ — $ (99) $ — $ (108) (1) Includes the embedded derivative in the commodity contract discussed above. We make a distinction between realized or unrealized gains and losses on derivatives. During the period when a derivative contract is outstanding, changes in the fair value of the derivative are recorded as an unrealized gain or loss. When a derivative contract matures or is settled, the previously recorded unrealized gain or loss is reversed and the realized gain or loss of the contract is recorded. The impact of MPLX’s derivative contracts not designated as hedging instruments and the location of gains and losses recognized on the Consolidated Statements of Income is summarized below: Three Months Ended March 31, (In millions) 2022 2021 Purchased product costs Realized loss $ (5) $ (3) Unrealized gain/(loss) 9 (3) Purchased product cost derivative gain/(loss) $ 4 $ (6)

Debt

Debt	3 Months Ended
	Mar. 31, 2022
Debt Disclosure [Abstract]
Debt	Debt MPLX’s outstanding borrowings consist of the following: (In millions) March 31, 2022 December 31, 2021 MPLX LP: MPLX Credit Agreement $ — $ 300 Fixed rate senior notes 20,032 18,532 Consolidated subsidiaries: MarkWest 23 23 ANDX 45 45 Financing lease obligations 8 9 Total 20,108 18,909 Unamortized debt issuance costs (116) (102) Unamortized discount/premium (236) (236) Amounts due within one year (999) (499) Total long-term debt due after one year $ 18,757 $ 18,072 Credit Agreement MPLX’s amended and restated credit agreement (as amended, the “MPLX Credit Agreement”), provides for borrowings up to $3.5 billion and a term that extends to July 2024. During the three months ended March 31, 2022, MPLX borrowed $900 million under the MPLX Credit Agreement, at an average interest rate of 1.451 percent, and repaid $1,200 million. At March 31, 2022, MPLX had no outstanding borrowings and less than $1 million in letters of credit outstanding under the MPLX Credit Agreement, resulting in total availability of $3.5 billion, or 100 percent of the borrowing capacity . Fixed Rate Senior Notes MPLX’s senior notes, including those issued by consolidated subsidiaries, consist of various series of senior notes maturing between 2022 and 2058 with interest rates ranging from 1.750 percent to 5.500 percent. Interest on each series of notes is payable semi-annually in arrears on various dates depending on the series of the notes. On March 14, 2022, MPLX issued $1.5 billion aggregate principal amount of 4.950 percent senior notes due March 2052 (the “2052 Senior Notes”) in an underwritten public offering. The 2052 Senior Notes were offered at a price to the public of 98.982 percent with interest payable semi-annually in arrears, commencing on September 14, 2022. The net proceeds were used to repay amounts outstanding under the MPC Intercompany Loan Agreement and the MPLX Credit Agreement.

Revenue

Revenue	3 Months Ended
	Mar. 31, 2022
Revenue from Contract with Customer [Abstract]
Revenue from Contract with Customer [Text Block]	Revenue Disaggregation of Revenue The following tables represent a disaggregation of revenue for each reportable segment for the three months ended March 31, 2022 and 2021: Three Months Ended March 31, 2022 (In millions) L&S G&P Total Revenues and other income: Service revenue $ 72 $ 482 $ 554 Service revenue - related parties 911 4 915 Service revenue - product related — 123 123 Product sales 1 496 497 Product sales - related parties 3 42 45 Total revenues from contracts with customers $ 987 $ 1,147 2,134 Non-ASC 606 revenue (1) 476 Total revenues and other income $ 2,610 Three Months Ended March 31, 2021 (In millions) L&S G&P Total Revenues and other income: Service revenue $ 84 $ 505 $ 589 Service revenue - related parties 869 3 872 Service revenue - product related — 77 77 Product sales 1 281 282 Product sales - related parties 3 39 42 Total revenues from contracts with customers $ 957 $ 905 1,862 Non-ASC 606 revenue (1) 477 Total revenues and other income $ 2,339 (1) Non-ASC 606 Revenue includes rental income, sales-type lease revenue, income from equity method investments, and other income. Contract Balances Contract assets typically relate to deficiency payments related to minimum volume commitments and aid in construction agreements where the revenue recognized and MPLX’s rights to consideration for work completed exceeds the amount billed to the customer. Contract assets are included in “Other current assets” and “Other noncurrent assets” on the Consolidated Balance Sheets. Contract liabilities, which we refer to as “Deferred revenue” and “Long-term deferred revenue,” typically relate to advance payments for aid in construction agreements and deferred customer credits associated with makeup rights and minimum volume commitments. Related to minimum volume commitments, breakage is estimated and recognized into service revenue in instances where it is probable the customer will not use the credit in future periods. We classify contract liabilities as current or long-term based on the timing of when we expect to recognize revenue. “Receivables, net” primarily relate to our commodity sales. Portions of the “Receivables, net” balance are attributed to the sale of commodity product controlled by MPLX prior to sale while a significant portion of the balance relates to the sale of commodity product on behalf of our producer customers. The sales and related “Receivables, net” are commingled and excluded from the table below. MPLX remits the net sales price back to our producer customers upon completion of the sale. Each period end, certain amounts within accounts payable relate to our payments to producer customers. Such amounts are not deemed material at period end as a result of when we settle with each producer. The tables below reflect the changes in our contract balances for the three-month periods ended March 31, 2022 and 2021: (In millions) Balance at December 31, 2021 (1) Additions/ (Deletions) Revenue Recognized (2) Balance at March 31, 2022 Contract assets $ 25 $ (18) $ — $ 7 Long-term contract assets 2 — — 2 Deferred revenue 56 11 (9) 58 Deferred revenue - related parties 60 34 (26) 68 Long-term deferred revenue 135 2 — 137 Long-term deferred revenue - related parties 31 — — 31 Long-term contract liabilities $ 5 $ — $ — $ 5 (In millions) Balance at December 31, 2020 (1) Additions/ (Deletions) Revenue Recognized (2) Balance at Contract assets $ 40 $ (27) $ — $ 13 Long-term contract assets 2 — — 2 Deferred revenue 37 7 (1) 43 Deferred revenue - related parties 91 21 (20) 92 Long-term deferred revenue 119 4 — 123 Long-term deferred revenue - related parties 48 (4) — 44 Long-term contract liabilities $ 6 $ — $ — $ 6 (1) Balance represents ASC 606 portion of each respective line item. (2) No significant revenue was recognized related to past performance obligations in the current periods. Remaining Performance Obligations The table below includes estimated revenue expected to be recognized in the future related to performance obligations that are unsatisfied (or partially unsatisfied) at the end of the reporting period. As of March 31, 2022, the amounts allocated to contract assets and contract liabilities on the Consolidated Balance Sheets are $293 million and are reflected in the amounts below. This will be recognized as revenue as the obligations are satisfied, which is expected to occur over the next 22 years. Further, MPLX does not disclose variable consideration due to volume variability in the table below. (In millions) 2022 $ 1,432 2023 1,771 2024 1,633 2025 1,560 2026 and thereafter 3,362 Total revenue on remaining performance obligations (1)(2)(3) $ 9,758 (1) All fixed consideration from contracts with customers is included in the amounts presented above. Variable consideration that is constrained or not required to be estimated as it reflects our efforts to perform is excluded. (2) Arrangements deemed implicit leases and sales-type leases are excluded from this table. (3) Only minimum volume commitments that are deemed fixed are included in the table above. MPLX has various minimum volume commitments in processing arrangements that vary based on the actual Btu content of the gas received. These amounts are deemed variable consideration and are excluded from the table above. We do not disclose information on the future performance obligations for any contract with an original expected duration of one year or less.

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	3 Months Ended
	Mar. 31, 2022
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information [Text Block]	Supplemental Cash Flow Information Three Months Ended March 31, (In millions) 2022 2021 Net cash provided by operating activities included: Interest paid (net of amounts capitalized) $ 213 $ 231 The Consolidated Statements of Cash Flows exclude changes to the Consolidated Balance Sheets that do not affect cash. The following is the change of additions to property, plant and equipment related to capital accruals: Three Months Ended March 31, (In millions) 2022 2021 Increase/(decrease) in capital accruals $ 3 $ (37)

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies Disclosure [Text Block]	Commitments and Contingencies MPLX is the subject of, or a party to, a number of pending or threatened legal actions, contingencies and commitments involving a variety of matters, including laws and regulations relating to the environment. Some of these matters are discussed below. For matters for which MPLX has not recorded a liability, MPLX is unable to estimate a range of possible loss because the issues involved have not been fully developed through pleadings, discovery or court proceedings. However, the ultimate resolution of some of these contingencies could, individually or in the aggregate, be material. Environmental Matters MPLX is subject to federal, state and local laws and regulations relating to the environment. These laws generally provide for control of pollutants released into the environment and require responsible parties to undertake remediation of hazardous waste disposal sites. Penalties may be imposed for non-compliance. At March 31, 2022 and December 31, 2021, accrued liabilities for remediation totaled $42 million and $23 million, respectively. It is not presently possible to estimate the ultimate amount of all remediation costs that might be incurred or the penalties, if any, that may be imposed. MPLX is involved in environmental enforcement matters arising in the ordinary course of business. While the outcome and impact to MPLX cannot be predicted with certainty, management believes the resolution of these environmental matters will not, individually or collectively, have a material adverse effect on its consolidated results of operations, financial position or cash flows. MPLX is also a party to a number of other lawsuits and other proceedings arising in the ordinary course of business. While the ultimate outcome and impact to MPLX cannot be predicted with certainty, management believes the resolution of these other lawsuits and proceedings will not, individually or collectively, have a material adverse effect on its consolidated financial position, results of operations or cash flows. Guarantees Over the years, MPLX has sold various assets in the normal course of its business. Certain of the related agreements contain performance and general guarantees, including guarantees regarding inaccuracies in representations, warranties, covenants and agreements, and environmental and general indemnifications that require MPLX to perform upon the occurrence of a triggering event or condition. These guarantees and indemnifications are part of the normal course of selling assets. MPLX is typically not able to calculate the maximum potential amount of future payments that could be made under such contractual provisions because of the variability inherent in the guarantees and indemnities. Most often, the nature of the guarantees and indemnities is such that there is no appropriate method for quantifying the exposure because the underlying triggering event has little or no past experience upon which a reasonable prediction of the outcome can be based. We hold a 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 referred to as the Bakken Pipeline system or DAPL. In 2020, the U.S. District Court for the District of Columbia (the “D.D.C.”) ordered the U.S. 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 EIS is currently expected to be completed in the second half of 2022. In May 2021, the D.D.C. denied a renewed request for an injunction to shut down the pipeline while the EIS is being prepared. In June 2021, the D.D.C. issued an order dismissing without prejudice the tribes’ claims against the Dakota Access Pipeline. The litigation could be reopened or new litigation challenging the EIS, once completed, could be filed. The pipeline remains operational. 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 pipeline were temporarily shut down, 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 shutdown. MPLX also expects to contribute its 9.19 percent pro rata share of any costs to remediate any deficiencies to reinstate the permit and/or return the pipeline into operation. If the vacatur of the easement permit 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, 2022, our maximum potential undiscounted payments under the Contingent Equity Contribution Agreement were approximately $170 million. Other Legal Proceedings In July 2020, Tesoro High Plains Pipeline Company, LLC (“THPP”), a subsidiary of MPLX, received a Notification of Trespass Determination from the Bureau of Indian Affairs (“BIA”) relating to a portion of the Tesoro High Plains Pipeline that crosses the Fort Berthold Reservation in North Dakota. The notification demanded the immediate cessation of pipeline operations and assessed trespass damages of approximately $187 million. On appeal, the Assistant Secretary - Indian Affairs issued an order vacating the BIA’s trespass order and remanded to the Regional Director for the BIA Great Plains Region to issue a new decision based on specific criteria. On December 15, 2020, the Regional Director of the BIA issued a new trespass notice to THPP, finding that THPP was in trespass and assessing trespass damages of approximately $4 million (including interest), which has been paid. The order also required that THPP immediately cease and desist use of the portion of the pipeline that crosses the property at issue. THPP has complied with the Regional Director’s December 15, 2020 notice. In March 2021, THPP received a copy of an order purporting to vacate all orders related to THPP’s alleged trespass issued by the BIA between July 2, 2020 and January 14, 2021. The order directs the Regional Director of the BIA to reconsider the issue of THPP’s alleged trespass and issue a new order, if necessary, after all interested parties have had an opportunity to be heard. Subsequently, landowners voluntarily dismissed the suit filed in the District of North Dakota. On April 23, 2021, THPP filed a lawsuit in the District of North Dakota against the United States of America, the U.S. Department of the Interior and the BIA (together, the “U.S. Government Parties”) challenging the March order purporting to vacate all previous orders related to THPP’s alleged trespass. On February 8, 2022, the U.S. Government Parties filed their answer to THPP’s suit, asserting counterclaims for trespass and ejectment. The U.S. Government Parties claim THPP is in continued trespass with respect to the pipeline and seek disgorgement of pipeline profits from June 1, 2013 to present, removal of the pipeline and remediation. We intend to vigorously defend ourselves against these counterclaims. We continue to work towards a settlement of this matter with holders of the property rights at issue. Contractual Commitments and Contingencies

Description of the Business a_2

Description of the Business and Basis of Presentation Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2022
Accounting Policies [Abstract]
Business Description and Basis of Presentation [Text Block]	Description of the Business and Basis of Presentation Description of the Business MPLX LP is a diversified, large-cap master limited partnership formed by Marathon Petroleum Corporation that owns and operates midstream energy infrastructure and logistics assets, and provides fuels distribution services. References in this report to “MPLX LP,” “MPLX,” “the Partnership,” “we,” “ours,” “us,” or like terms refer to MPLX LP and its subsidiaries. References to “MPC” refer collectively to Marathon Petroleum Corporation as our sponsor and its subsidiaries, other than the Partnership. We are engaged in the gathering, transportation, storage and distribution of crude oil, refined products and other hydrocarbon-based products; the gathering, processing and transportation of natural gas; and the gathering, transportation, fractionation, storage and marketing of NGLs. MPLX’s principal executive office is located in Findlay, Ohio. MPLX’s business consists of two segments based on the nature of services it offers: Logistics and Storage (“L&S”), which relates primarily to crude oil, refined products and other hydrocarbon-based products; and Gathering and Processing (“G&P”), which relates primarily to natural gas and NGLs. See Note 7 for additional information regarding the operations and results of these segments. Basis of Presentation The accompanying interim consolidated financial statements are unaudited; however, in the opinion of MPLX’s management, these statements reflect all adjustments necessary for a fair statement of the results for the periods reported. All such adjustments are of a normal, recurring nature unless otherwise disclosed. These interim consolidated financial statements, including the notes, have been prepared in accordance with the rules and regulations of the SEC applicable to interim period financial statements and do not include all of the information and disclosures required by GAAP for complete financial statements. Certain information derived from our audited annual financial statements, prepared in accordance with GAAP, has been condensed or omitted from these interim financial statements. These interim consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in our Annual Report on Form 10-K for the year ended December 31, 2021. The results of operations for the three months ended March 31, 2022 are not necessarily indicative of the results to be expected for the full year. MPLX’s consolidated financial statements include all majority-owned and controlled subsidiaries. For non-wholly owned consolidated subsidiaries, the interests owned by third parties have been recorded as “Noncontrolling interests” on the accompanying Consolidated Balance Sheets. Intercompany investments, accounts and transactions have been eliminated. MPLX’s investments in which MPLX exercises significant influence but does not control and does not have a controlling financial interest are accounted for using the equity method. MPLX’s investments in VIEs in which MPLX exercises significant influence but does not control and is not the primary beneficiary are also accounted for using the equity method.
Use of Estimates, Policy [Policy Text Block]	The accompanying interim consolidated financial statements are unaudited; however, in the opinion of MPLX’s management, these statements reflect all adjustments necessary for a fair statement of the results for the periods reported. All such adjustments are of a normal, recurring nature unless otherwise disclosed. These interim consolidated financial statements, including the notes, have been prepared in accordance with the rules and regulations of the SEC applicable to interim period financial statements and do not include all of the information and disclosures required by GAAP for complete financial statements. Certain information derived from our audited annual financial statements, prepared in accordance with GAAP, has been condensed or omitted from these interim financial statements.
Consolidation, Subsidiaries or Other Investments, Consolidated Entities, Policy [Policy Text Block]	MPLX’s consolidated financial statements include all majority-owned and controlled subsidiaries. For non-wholly owned consolidated subsidiaries, the interests owned by third parties have been recorded as “Noncontrolling interests” on the accompanying Consolidated Balance Sheets. Intercompany investments, accounts and transactions have been eliminated. MPLX’s investments in which MPLX exercises significant influence but does not control and does not have a controlling financial interest are accounted for using the equity method. MPLX’s investments in VIEs in which MPLX exercises significant influence but does not control and is not the primary beneficiary are also accounted for using the equity method.Certain prior period financial statement amounts have been reclassified to conform to current period presentation.
Nature of Operations	We are engaged in the gathering, transportation, storage and distribution of crude oil, refined products and other hydrocarbon-based products; the gathering, processing and transportation of natural gas; and the gathering, transportation, fractionation, storage and marketing of NGLs. MPLX’s principal executive office is located in Findlay, Ohio.MPLX’s business consists of two segments based on the nature of services it offers: Logistics and Storage (“L&S”), which relates primarily to crude oil, refined products and other hydrocarbon-based products; and Gathering and Processing (“G&P”), which relates primarily to natural gas and NGLs. See Note 7 for additional information regarding the operations and results of these segments.

Net Income Per Limited Partne_2

Net Income Per Limited Partner Unit Accounting Policy (Policies)	3 Months Ended
	Mar. 31, 2022
Accounting Policies [Abstract]
Earnings Per Share, Policy [Policy Text Block]	Net income/(loss) per unit applicable to common units is computed by dividing net income attributable to MPLX LP less income allocated to participating securities by the weighted average number of common units outstanding.

Investments and Noncontrollin_2

Investments and Noncontrolling Interests (Tables)	3 Months Ended
	Mar. 31, 2022
Equity Method Investments and Joint Ventures [Abstract]
Equity Method Investments [Table Text Block]	The following table presents MPLX’s equity method investments at the dates indicated: Ownership as of Carrying value at March 31, March 31, December 31, (In millions, except ownership percentages) 2022 2022 2021 L&S MarEn Bakken Company LLC (1) 25% $ 502 $ 449 Illinois Extension Pipeline Company, L.L.C. 35% 249 243 LOOP LLC 41% 274 265 Andeavor Logistics Rio Pipeline LLC (2) 67% 181 183 Minnesota Pipe Line Company, LLC 17% 182 183 Whistler Pipeline LLC (2) 38% 166 155 Explorer Pipeline Company 25% 65 66 W2W Holdings LLC (2) 50% 56 58 Other (2) 125 116 Total L&S 1,800 1,718 G&P MarkWest Utica EMG, L.L.C. (2) 57% 681 680 Sherwood Midstream LLC (2) 50% 539 544 MarkWest EMG Jefferson Dry Gas Gathering Company, L.L.C. (2) 67% 336 332 MarkWest Torñado GP, L.L.C. (2) 60% 266 246 Rendezvous Gas Services, L.L.C. (2) 78% 145 147 Sherwood Midstream Holdings LLC (2) 51% 133 136 Centrahoma Processing LLC 40% 133 133 Other (2) 46 45 Total G&P 2,279 2,263 Total $ 4,079 $ 3,981 (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 referred to as the Bakken Pipeline system or DAPL. (2) Investments deemed to be VIEs. Some investments included within “Other” have also been deemed to be VIEs.
Summarized Financial Information For Equity Method Investees Table [Table Text Block]	Summarized financial information for MPLX’s equity method investments for the three months ended March 31, 2022 and 2021 is as follows: Three Months Ended March 31, 2022 (In millions) VIEs Non-VIEs Total Revenues and other income $ 249 $ 308 $ 557 Costs and expenses 137 129 266 Income from operations 112 179 291 Net income 103 166 269 Income from equity method investments $ 55 $ 44 $ 99 Three Months Ended March 31, 2021 (In millions) VIEs Non-VIEs Total Revenues and other income $ 163 $ 284 $ 447 Costs and expenses 107 131 238 Income from operations 56 153 209 Net income 64 140 204 Income from equity method investments $ 39 $ 31 $ 70 Summarized balance sheet information for MPLX’s equity method investments as of March 31, 2022 and December 31, 2021 is as follows: March 31, 2022 (In millions) VIEs Non-VIEs Total Current assets $ 386 $ 370 $ 756 Noncurrent assets 7,482 4,875 12,357 Current liabilities 773 259 1,032 Noncurrent liabilities $ 1,929 $ 789 $ 2,718 December 31, 2021 (In millions) VIEs Non-VIEs Total Current assets $ 335 $ 411 $ 746 Noncurrent assets 7,439 4,895 12,334 Current liabilities 217 310 527 Noncurrent liabilities $ 2,461 $ 788 $ 3,249

Related Party Agreements and _2

Related Party Agreements and Transactions (Tables)	3 Months Ended
	Mar. 31, 2022
Related Party Transactions [Abstract]
Schedule of Short-term Debt	Activity on the MPC Loan Agreement was as follows: Three Months Ended March 31, (In millions) 2022 2021 Borrowings $ 1,849 $ 2,241 Average interest rate of borrowings 1.400 % 1.371 % Repayments $ 2,976 $ 2,241 Outstanding balance at end of period $ 323 $ —
Schedule of Related Party Transactions [Table Text Block]	(In millions) March 31, 2022 December 31, 2021 Current assets - related parties Receivables $ 707 $ 555 Prepaid 17 4 Other 3 3 Lease receivables 86 82 Total 813 644 Noncurrent assets - related parties Long-term receivables 30 31 Right of use assets 229 229 Long-term lease receivables 828 854 Unguaranteed residual asset 64 47 Total 1,151 1,161 Current liabilities - related parties MPC loan agreement and other payables (1) 606 1,702 Operating lease liabilities 1 1 Deferred revenue - Minimum volume deficiencies 38 35 Deferred revenue - Project reimbursements 42 42 Total 687 1,780 Long-term liabilities - related parties Long-term operating lease liabilities 228 228 Long-term deferred revenue - Project reimbursements 77 74 Total $ 305 $ 302 (1) Includes $323 million as of March 31, 2022 and $1,450 million as of December 31, 2021 related to outstanding borrowings on the intercompany loan with MPC, which are included in “Current liabilities - related parties” on the Consolidated Balance Sheets.

Equity (Tables)

Equity (Tables)	3 Months Ended
	Mar. 31, 2022
Equity [Abstract]
Schedule of Stockholders Equity [Table Text Block]	The changes in the number of common units during the three months ended March 31, 2022 are summarized below: (In units) Common Balance at December 31, 2021 1,016,178,378 Unit-based compensation awards 148,951 Units redeemed in unit repurchase program (3,119,522) Balance at March 31, 2022 1,013,207,807
Distributions Made to Limited Partner, by Distribution [Table Text Block]	The allocation of total quarterly cash distributions to limited and preferred unitholders is as follows for the three months ended March 31, 2022 and 2021. Distributions, although earned, are not accrued until declared. MPLX’s distributions are declared subsequent to quarter end; therefore, the following table represents total cash distributions applicable to the period in which the distributions were earned. Three Months Ended March 31, (In millions) 2022 2021 Common and preferred unit distributions: Common unitholders, includes common units of general partner $ 713 $ 707 Series A preferred unit distributions 21 20 Series B preferred unit distributions 11 11 Total cash distributions declared $ 745 $ 738

Net Income Per Limited Partne_3

Net Income Per Limited Partner Unit (Tables)	3 Months Ended
	Mar. 31, 2022
Earnings Per Share [Abstract]
Schedule of Distributions By Partner By Class [Table Text Block]	During the three months ended March 31, 2022 and 2021, MPLX had participating securities consisting of common units, certain equity-based compensation awards, Series A preferred units and Series B preferred units and had dilutive potential common units consisting of certain equity-based compensation awards. Potential common units omitted from the diluted earnings per unit calculation for the three months ended March 31, 2022 and 2021 were less than 1 million. Three Months Ended March 31, (In millions) 2022 2021 Net income attributable to MPLX LP $ 825 $ 739 Less: Distributions declared on Series A preferred units 21 20 Distributions declared on Series B preferred units 11 11 Limited partners’ distributions declared on MPLX common units (including common units of general partner) 713 707 Undistributed net gain attributable to MPLX LP $ 80 $ 1
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]	Three Months Ended March 31, 2022 (In millions, except per unit data) Limited Partners’ Series A Preferred Units Series B Preferred Units Total Basic and diluted net income attributable to MPLX LP per unit Net income attributable to MPLX LP: Distributions declared $ 713 $ 21 $ 11 $ 745 Undistributed net gain attributable to MPLX LP 78 2 — 80 Net income attributable to MPLX LP (1) $ 791 $ 23 $ 11 $ 825 Weighted average units outstanding: Basic 1,015 Diluted 1,015 Net income attributable to MPLX LP per limited partner unit: Basic $ 0.78 Diluted $ 0.78 (1) Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period. Three Months Ended March 31, 2021 (In millions, except per unit data) Limited Partners’ Series A Preferred Units Series B Preferred Units Total Basic and diluted net income attributable to MPLX LP per unit Net income attributable to MPLX LP: Distributions declared $ 707 $ 20 $ 11 $ 738 Undistributed net gain attributable to MPLX LP 1 — — 1 Net income attributable to MPLX LP (1) $ 708 $ 20 $ 11 $ 739 Weighted average units outstanding: Basic 1,037 Diluted 1,037 Net income attributable to MPLX LP per limited partner unit: Basic $ 0.68 Diluted $ 0.68 (1) Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

Segment Information (Tables)

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2022
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment [Table Text Block]	The tables below present information about revenues and other income, Segment Adjusted EBITDA, restructuring expenses, capital expenditures and investments in unconsolidated affiliates for our reportable segments: Three Months Ended March 31, (In millions) 2022 2021 L&S Service revenue $ 983 $ 953 Rental income 175 249 Product related revenue 4 4 Sales-type lease revenue 111 37 Income from equity method investments 52 36 Other income 12 15 Total segment revenues and other income (1) 1,337 1,294 Segment Adjusted EBITDA (2) 904 896 Capital expenditures 77 59 Investments in unconsolidated affiliates 68 9 G&P Service revenue 486 508 Rental income 81 92 Product related revenue 661 397 Income from equity method investments 47 34 Other income/(loss) (2) 14 Total segment revenues and other income (1) 1,273 1,045 Segment Adjusted EBITDA (2) 489 456 Capital expenditures 95 30 Investments in unconsolidated affiliates $ 42 $ 26 (1) Within the total segment revenues and other income amounts presented above, third party revenues for the L&S segment were $135 million and $129 million for the three months ended March 31, 2022 and March 31, 2021, respectively. Third party revenues for the G&P segment were $1,212 million and $989 million for the three months ended March 31, 2022 and March 31, 2021, respectively. (2) See below for the reconciliation from Segment Adjusted EBITDA to “Net income.”
Reconciliation of Other Significant Reconciling Items from Segments to Consolidated [Table Text Block]	The table below provides a reconciliation between “Net income” and Segment Adjusted EBITDA. Three Months Ended March 31, (In millions) 2022 2021 Reconciliation to Net income: L&S Segment Adjusted EBITDA $ 904 $ 896 G&P Segment Adjusted EBITDA 489 456 Total reportable segments 1,393 1,352 Depreciation and amortization (1) (313) (329) Interest and other financial costs (222) (225) Income from equity method investments 99 70 Distributions/adjustments related to equity method investments (132) (121) Other (1) (9) Adjusted EBITDA attributable to noncontrolling interests 9 10 Net income $ 833 $ 748 (1) Depreciation and amortization attributable to L&S was $130 million and $147 million for the three months ended March 31, 2022 and March 31, 2021, respectively. Depreciation and amortization attributable to G&P was $183 million and $182 million for the three months ended March 31, 2022 and March 31, 2021, respectively.

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	3 Months Ended
	Mar. 31, 2022
Property, Plant and Equipment [Abstract]
Summary of Property, Plant and Equipment	Property, plant and equipment with associated accumulated depreciation is shown below: March 31, 2022 December 31, 2021 (In millions) Gross PP&E Accumulated Depreciation Net PP&E Gross PP&E Accumulated Depreciation Net PP&E L&S $ 12,438 $ 3,347 $ 9,091 $ 12,371 $ 3,227 $ 9,144 G&P 14,253 3,432 10,821 14,175 3,277 10,898 Total $ 26,691 $ 6,779 $ 19,912 $ 26,546 $ 6,504 $ 20,042

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2022
Fair Value Disclosures [Abstract]
Fair Value Inputs Assets and Liabilities Quantitative Information [Table Text Block]	Level 3 instruments relate to an embedded derivative liability for a natural gas purchase commitment embedded in a keep-whole processing agreement. The fair value calculation for these Level 3 instruments used significant unobservable inputs including: (1) NGL prices interpolated and extrapolated due to inactive markets ranging from $0.73 to $2.38 per gallon with a weighted average of $0.97 per gallon and (2) the probability of renewal of 100 percent for the five
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block]	The following table is a reconciliation of the net beginning and ending balances recorded for net assets and liabilities classified as Level 3 in the fair value hierarchy. Three Months Ended March 31, 2022 2021 (In millions) Embedded Derivatives in Commodity Contracts (net) Embedded Derivatives in Commodity Contracts (net) Fair value at beginning of period $ (108) $ (63) Total gain/(loss) (realized and unrealized) included in earnings (1) 4 (6) Settlements 5 3 Fair value at end of period (99) (66) The amount of total gain/(loss) for the period included in earnings attributable to the change in unrealized gain/(loss) relating to liabilities still held at end of period $ 5 $ (5) (1) Gain/(loss) on derivatives embedded in commodity contracts are recorded in “Purchased product costs” on the Consolidated Statements of Income.
Fair Value Carrying Value by Balance Sheet Grouping [Table Text Block]	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, 2022 December 31, 2021 (In millions) Fair Value Carrying Value Fair Value Carrying Value Outstanding debt (1) $ 20,392 $ 19,864 $ 20,779 $ 18,664 (1) 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” on the Consolidated Balance Sheets.

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2022
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block]	The impact of MPLX’s derivative instruments on its Consolidated Balance Sheets is summarized below: (In millions) March 31, 2022 December 31, 2021 Derivative contracts not designated as hedging instruments and their balance sheet location Asset Liability Asset Liability Commodity contracts (1) Other current assets / Other current liabilities $ — $ (16) $ — $ (15) Other noncurrent assets / Deferred credits and other liabilities — (83) — (93) Total $ — $ (99) $ — $ (108) (1) Includes the embedded derivative in the commodity contract discussed above.
Derivative Instruments, Gain (Loss) [Table Text Block]	The impact of MPLX’s derivative contracts not designated as hedging instruments and the location of gains and losses recognized on the Consolidated Statements of Income is summarized below: Three Months Ended March 31, (In millions) 2022 2021 Purchased product costs Realized loss $ (5) $ (3) Unrealized gain/(loss) 9 (3) Purchased product cost derivative gain/(loss) $ 4 $ (6)

Debt (Tables)

Debt (Tables)	3 Months Ended
	Mar. 31, 2022
Debt Disclosure [Abstract]
Schedule of Debt [Table Text Block]	MPLX’s outstanding borrowings consist of the following: (In millions) March 31, 2022 December 31, 2021 MPLX LP: MPLX Credit Agreement $ — $ 300 Fixed rate senior notes 20,032 18,532 Consolidated subsidiaries: MarkWest 23 23 ANDX 45 45 Financing lease obligations 8 9 Total 20,108 18,909 Unamortized debt issuance costs (116) (102) Unamortized discount/premium (236) (236) Amounts due within one year (999) (499) Total long-term debt due after one year $ 18,757 $ 18,072

Revenue (Tables)

Revenue (Tables)	3 Months Ended
	Mar. 31, 2022
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue [Table Text Block]	The following tables represent a disaggregation of revenue for each reportable segment for the three months ended March 31, 2022 and 2021: Three Months Ended March 31, 2022 (In millions) L&S G&P Total Revenues and other income: Service revenue $ 72 $ 482 $ 554 Service revenue - related parties 911 4 915 Service revenue - product related — 123 123 Product sales 1 496 497 Product sales - related parties 3 42 45 Total revenues from contracts with customers $ 987 $ 1,147 2,134 Non-ASC 606 revenue (1) 476 Total revenues and other income $ 2,610 Three Months Ended March 31, 2021 (In millions) L&S G&P Total Revenues and other income: Service revenue $ 84 $ 505 $ 589 Service revenue - related parties 869 3 872 Service revenue - product related — 77 77 Product sales 1 281 282 Product sales - related parties 3 39 42 Total revenues from contracts with customers $ 957 $ 905 1,862 Non-ASC 606 revenue (1) 477 Total revenues and other income $ 2,339
Contract with Customer, Contract Asset, Contract Liability, and Receivable [Table Text Block]	The tables below reflect the changes in our contract balances for the three-month periods ended March 31, 2022 and 2021: (In millions) Balance at December 31, 2021 (1) Additions/ (Deletions) Revenue Recognized (2) Balance at March 31, 2022 Contract assets $ 25 $ (18) $ — $ 7 Long-term contract assets 2 — — 2 Deferred revenue 56 11 (9) 58 Deferred revenue - related parties 60 34 (26) 68 Long-term deferred revenue 135 2 — 137 Long-term deferred revenue - related parties 31 — — 31 Long-term contract liabilities $ 5 $ — $ — $ 5 (In millions) Balance at December 31, 2020 (1) Additions/ (Deletions) Revenue Recognized (2) Balance at Contract assets $ 40 $ (27) $ — $ 13 Long-term contract assets 2 — — 2 Deferred revenue 37 7 (1) 43 Deferred revenue - related parties 91 21 (20) 92 Long-term deferred revenue 119 4 — 123 Long-term deferred revenue - related parties 48 (4) — 44 Long-term contract liabilities $ 6 $ — $ — $ 6 (1) Balance represents ASC 606 portion of each respective line item.
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table Text Block]	As of March 31, 2022, the amounts allocated to contract assets and contract liabilities on the Consolidated Balance Sheets are $293 million and are reflected in the amounts below. This will be recognized as revenue as the obligations are satisfied, which is expected to occur over the next 22 years. Further, MPLX does not disclose variable consideration due to volume variability in the table below. (In millions) 2022 $ 1,432 2023 1,771 2024 1,633 2025 1,560 2026 and thereafter 3,362 Total revenue on remaining performance obligations (1)(2)(3) $ 9,758 (1) All fixed consideration from contracts with customers is included in the amounts presented above. Variable consideration that is constrained or not required to be estimated as it reflects our efforts to perform is excluded. (2) Arrangements deemed implicit leases and sales-type leases are excluded from this table. (3) Only minimum volume commitments that are deemed fixed are included in the table above. MPLX has various minimum volume commitments in processing arrangements that vary based on the actual Btu content of the gas received. These amounts are deemed variable consideration and are excluded from the table above. We do not disclose information on the future performance obligations for any contract with an original expected duration of one year or less.

Supplemental Cash Flow Inform_2

Supplemental Cash Flow Information (Tables)	3 Months Ended
	Mar. 31, 2022
Supplemental Cash Flow Elements [Abstract]
Summary of Supplemental Cash Flow Information [Table Text Block]	Three Months Ended March 31, (In millions) 2022 2021 Net cash provided by operating activities included: Interest paid (net of amounts capitalized) $ 213 $ 231
Summary of Reconciliation of Additions to Property, Plant and Equipment to Total Capital Expenditures [Table Text Block]	The Consolidated Statements of Cash Flows exclude changes to the Consolidated Balance Sheets that do not affect cash. The following is the change of additions to property, plant and equipment related to capital accruals: Three Months Ended March 31, (In millions) 2022 2021 Increase/(decrease) in capital accruals $ 3 $ (37)

Description of Business and Bas

Description of Business and Basis of Presentation - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2022
Accounting Policies [Abstract]
Number of reportable segments	2

Investments and Noncontrollin_3

Investments and Noncontrolling Interests (Summary of Equity Method Investment Financial Information) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Schedule of Equity Method Investments [Line Items]
Equity method investments		$ 4,079		$ 3,981
Revenues		2,610	$ 2,339
Costs and Expenses		1,550	1,365
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		833	748
Income from equity method investments		99	70
Assets, Current		1,798		1,507
Liabilities, Current		$ 2,858		3,348
MarEn Bakken Company LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		25.00%
Illinois Extension
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		35.00%
LOOP
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		41.00%
Andeavor Logistics Rio Pipeline [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		67.00%
Minnesota Pipe Line Company, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		17.00%
Whistler Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		38.00%
Explorer
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		25.00%
W2W Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		50.00%
MarkWest Utica EMG
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		57.00%
Sherwood Midstream
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		50.00%
MarkWest EMG Jefferson Dry Gas Gathering Company, L.L.C. [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		67.00%
MarkWest Tornado GP, L.L.C.
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		60.00%
Rendezvous Gas Services, L.L.C. [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		78.00%
Centrahoma Processing LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		40.00%
Indirect Ownership Interest [Member] | Bakken Pipeline System [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		9.19%
Indirect Ownership Interest [Member] | Sherwood Midstream Holdings
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		24.55%
Direct Ownership Interest [Member] | Sherwood Midstream Holdings
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		51.00%
G&P | MarkWest Utica EMG
Schedule of Equity Method Investments [Line Items]
Equity method investments	[1]	$ 681		680
G&P | Sherwood Midstream
Schedule of Equity Method Investments [Line Items]
Equity method investments	[1]	539		544
G&P | MarkWest EMG Jefferson Dry Gas Gathering Company, L.L.C. [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[1]	336		332
G&P | MarkWest Tornado GP, L.L.C.
Schedule of Equity Method Investments [Line Items]
Equity method investments	[1]	266		246
G&P | Rendezvous Gas Services, L.L.C. [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[1]	145		147
G&P | Sherwood Midstream Holdings
Schedule of Equity Method Investments [Line Items]
Equity method investments	[1]	133		136
G&P | Centrahoma Processing LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments		133		133
G&P | Other VIEs and Non-VIEs [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[1]	46		45
L&S | MarEn Bakken Company LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[2]	502		449
L&S | Illinois Extension
Schedule of Equity Method Investments [Line Items]
Equity method investments		249		243
L&S | LOOP
Schedule of Equity Method Investments [Line Items]
Equity method investments		274		265
L&S | Andeavor Logistics Rio Pipeline [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[1]	181		183
L&S | Minnesota Pipe Line Company, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments		182		183
L&S | Whistler Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[1]	166		155
L&S | Explorer
Schedule of Equity Method Investments [Line Items]
Equity method investments		65		66
L&S | W2W Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[1]	56		58
L&S | Other VIEs and Non-VIEs [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[1]	125		116
Operating Segments | G&P
Schedule of Equity Method Investments [Line Items]
Equity method investments		2,279		2,263
Revenues	[3]	1,273	1,045
Income from equity method investments		47	34
Operating Segments | L&S
Schedule of Equity Method Investments [Line Items]
Equity method investments		1,800		1,718
Revenues	[3]	1,337	1,294
Income from equity method investments		52	36
Other VIEs and Non-VIEs [Member]
Schedule of Equity Method Investments [Line Items]
Revenues		557	447
Costs and Expenses		266	238
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest		291	209
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		269	204
Assets, Current		756		746
Assets, Noncurrent		12,357		12,334
Liabilities, Current		1,032		527
Liabilities, Noncurrent		2,718		3,249
Non-VIEs [Member]
Schedule of Equity Method Investments [Line Items]
Revenues		308	284
Costs and Expenses		129	131
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest		179	153
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		166	140
Income from equity method investments		44	31
Assets, Current		370		411
Assets, Noncurrent		4,875		4,895
Liabilities, Current		259		310
Liabilities, Noncurrent		789		788
Other VIEs [Member]
Schedule of Equity Method Investments [Line Items]
Revenues		249	163
Costs and Expenses		137	107
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest		112	56
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		103	64
Income from equity method investments		55	$ 39
Assets, Current		386		335
Assets, Noncurrent		7,482		7,439
Liabilities, Current		773		217
Liabilities, Noncurrent		$ 1,929		$ 2,461
[1]	Investments deemed to be VIEs. Some investments included within “Other” have also been deemed to be VIEs.
[2]	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 referred to as the Bakken Pipeline system or DAPL.
[3]	Within the total segment revenues and other income amounts presented above, third party revenues for the L&S segment were $135 million and $129 million for the three months ended March 31, 2022 and March 31, 2021, respectively. Third party revenues for the G&P segment were $1,212 million and $989 million for the three months ended March 31, 2022 and March 31, 2021, respectively.

Related Party Agreements and _3

Related Party Agreements and Transactions MPC Loan Agreement (Details) - Related Party Revolving Credit Agreement [Member] - MPC Investment [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Related Party Transaction [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 1,500
Debt Instrument, Description of Variable Rate Basis	LIBOR plus 1.25 percent
Related party debt - borrowings	$ 1,849	$ 2,241
Line of Credit Facility, Interest Rate During Period	1.40%	1.371%
Repayments of Lines of Credit	$ 2,976	$ 2,241
Line of Credit, Current	$ 323	$ 0	$ 1,450

Related Party Disclosures (Deta

Related Party Disclosures (Details) - Marathon Petroleum Corporation [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Related Party Transaction [Line Items]
Sales Revenue, Goods, Related Party, Net Zero	$ 293	$ 168
Asset under Construction [Member]
Related Party Transaction [Line Items]
Property, Plant and Equipment, Additions	$ 19	$ 12

Summary of Charges for Employee

Summary of Charges for Employee Services and Omnibus Agreements (Details) - Marathon Petroleum Corporation [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Related Party Transaction [Line Items]
General and Administrative Expense	$ 55	$ 57
Asset under Construction [Member]
Related Party Transaction [Line Items]
Property, Plant and Equipment, Additions	$ 19	$ 12

Other Assets and Liabilities fr

Other Assets and Liabilities from Related Parties (Details) - USD ($) $ in Millions		Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021
Affiliated Entity
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties, Current		$ 707	$ 555
Prepaid Insurance		17	4
Other current assets		3	3
Sales-type Lease, Interest Income		86	82
Current Assets, Related Parties		813	644
Accounts Receivable, Related Parties, Noncurrent		30	31
Due from Related Parties, Noncurrent		1,151	1,161
Accounts Payable, Related Parties, Current	[1]	606	1,702
Operating Lease, Right-of-Use Asset		229	229
Net Investment in Lease, Noncurrent		828	854
Sales-type Lease, Unguaranteed Residual Asset		64	47
Due to Related Parties, Current		687	1,780
Operating Lease, Liability, Current		1	1
Operating Lease, Liability, Noncurrent		228	228
Liabilities, Related Parties, Noncurrent		305	302
MPC Investment [Member] | Related Party Revolving Credit Agreement [Member]
Related Party Transaction [Line Items]
Line of Credit, Current		323	1,450	$ 0
Minimum Committed Volume Contracts [Member] | Affiliated Entity
Related Party Transaction [Line Items]
Deferred Revenue Related Parties		38	35
Reimbursable Projects [Member] | Affiliated Entity
Related Party Transaction [Line Items]
Deferred Revenue Related Parties		42	42
Deferred Revenue, Noncurrent, Related Parties		$ 77	$ 74
[1]	Includes $323 million as of March 31, 2022 and $1,450 million as of December 31, 2021 related to outstanding borrowings on the intercompany loan with MPC, which are included in “Current liabilities - related parties” on the Consolidated Balance Sheets.

Equity - Changes in Partners Ca

Equity - Changes in Partners Capital, Unit Rollforward (Details) - USD ($) $ / shares in Units, $ in Millions	Apr. 26, 2022	Feb. 15, 2022	Apr. 27, 2021	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2023	Dec. 31, 2021	Nov. 02, 2020
Stockholders Equity [Line Items]
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders				$ (746)	$ (745)
Distribution Made to Limited Partner, Cash Distributions Declared				$ 745	738
Stock Repurchase Program, Authorized Amount								$ 1,000
Treasury Stock Acquired, Average Cost Per Share				$ 32.06
Stock Repurchase Program, Remaining Authorized Repurchase Amount				$ 237
Cash distributions declared per limited partner common unit			$ 0.6875
Payments for Repurchase of Common Stock				$ 100	155
Limited Partners Common Units [Member]
Stockholders Equity [Line Items]
Balance at December 31, 2021				1,016,178,378
Unit-based compensation awards				148,951
Stock Repurchased and Retired During Period, Shares				3,119,522
Balance at March 31, 2022				1,013,207,807
Distribution Made to Limited Partner, Cash Distributions Declared				$ 713	707
Series B Preferred Stock [Member]
Stockholders Equity [Line Items]
Preferred Units, Outstanding				600,000			600,000
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders				$ (21)	(21)
Subsequent Event
Stockholders Equity [Line Items]
Cash distributions declared per limited partner common unit	$ 0.7050
Series B Preferred Stock [Member]
Stockholders Equity [Line Items]
Preferred Units, Outstanding				600,000
Dividend rate, percentage				6.875%
Price per share				$ 1,000
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders		$ (21)
Preferred Stock, Redemption Terms				MPLX has the right to redeem some or all of the Series B preferred units, at any time, on or after February 15, 2023 at the Series B preferred unit redemption price of $1,000 per unit, plus any accumulated and unpaid distributions up to the redemption date.
Series B Preferred Stock [Member] | Preferred Partner [Member]
Stockholders Equity [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared				$ 11	$ 11
Cash distributions declared per limited partner common unit				$ 68.75
Series B Preferred Stock [Member] | Subsequent Event
Stockholders Equity [Line Items]
Dividend rate, percentage						4.652%
Preferred Stock, Dividend Payment Rate, Variable						LIBOR plus

Equity - Cash Distributions (De

Equity - Cash Distributions (Details) - USD ($) $ / shares in Units, $ in Millions	May 13, 2022	May 06, 2022	Apr. 26, 2022	Feb. 15, 2022	Apr. 27, 2021	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2023
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared						$ 745	$ 738
Cash distributions declared per limited partner common unit					$ 0.6875
Partners' Capital Account, Distributions						$ 746	745
Series B Preferred Stock [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Preferred Units, Outstanding						600,000
Distribution date				Feb. 15, 2022
Partners' Capital Account, Distributions				$ 21
Preferred Stock, Dividend Rate, Percentage						6.875%
Subsequent Event
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution Made to Limited Partner, Declaration Date			Apr. 26, 2022
Cash distributions declared per limited partner common unit			$ 0.7050
Distribution date	May 13, 2022
Date of record		May 6, 2022
Subsequent Event | Series B Preferred Stock [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Preferred Stock, Dividend Payment Rate, Variable								LIBOR plus
Preferred Stock, Dividend Rate, Percentage								4.652%
Limited Partners Common Units [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared						$ 713	707
Series A Preferred Stock [Member] | Series B Preferred Stock [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared						$ 11	11
Cash distributions declared per limited partner common unit						$ 68.75
Series A Preferred Stock [Member] | Series A Preferred Stock [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared						$ 21	$ 20

Net Income Per Limited Partne_4

Net Income Per Limited Partner Unit - Schedule of Distributions by Partner by Class (Details) - USD ($) shares in Millions, $ in Millions		3 Months Ended
		Mar. 31, 2022	Mar. 31, 2021
Net Income Per Share [Line Items]
Potentially dilutive units		1	1
Net Income (Loss) Attributable to Parent	[1]	$ 825	$ 739
Distribution Made to Limited Partner, Cash Distributions Declared		745	738
Undistributed net income (loss) attributable to MPLX LP		80	1
Limited Partners Common Units [Member]
Net Income Per Share [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared		713	707
Undistributed net income (loss) attributable to MPLX LP		78	1
Series A Preferred Stock [Member] | Series A Preferred Stock [Member]
Net Income Per Share [Line Items]
Net Income (Loss) Attributable to Parent	[1]	23	20
Distribution Made to Limited Partner, Cash Distributions Declared		21	20
Undistributed net income (loss) attributable to MPLX LP		2	0
Series B Preferred Stock [Member] | Series A Preferred Stock [Member]
Net Income Per Share [Line Items]
Net Income (Loss) Attributable to Parent	[1]	11	11
Distribution Made to Limited Partner, Cash Distributions Declared		11	11
Undistributed net income (loss) attributable to MPLX LP		0	0
Common Stock | Limited Partners Common Units [Member]
Net Income Per Share [Line Items]
Net Income (Loss) Attributable to Parent	[1]	$ 791	$ 708
[1]	Allocation of net income attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

Net Income Per Limited Partne_5

Net Income Per Limited Partner Unit - Basic and Diluted Earnings Per Unit (Details) - Limited Partners Common Units [Member] - $ / shares shares in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Weighted average units outstanding:
Common - basic (in shares)	1,015	1,037
Common - diluted (in shares)	1,015	1,037
Net Income (Loss), Per Outstanding Limited Partnership Unit, Basic, Net of Tax	$ 0.78	$ 0.68
Common - diluted (in USD per unit)	$ 0.78	$ 0.68

Segment Information (Details)

Segment Information (Details)	3 Months Ended
	Mar. 31, 2022
Segment Reporting [Abstract]
Number of reportable segments	2

Segment Information - Segment A

Segment Information - Segment Adjusted EBITDA (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2022	Mar. 31, 2021
Segment Reporting Information [Line Items]
Income from equity method investments		$ 99	$ 70
Total segment revenues and other income		(2,610)	(2,339)
Payments to Acquire Equity Method Investments		(110)	(35)
L&S
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		987	957
Payments to Acquire Equity Method Investments		(68)	(9)
L&S | Marathon Petroleum Corporation [Member]
Segment Reporting Information [Line Items]
Sales-type Lease, Revenue		111	37
G&P
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		1,147	905
Payments to Acquire Equity Method Investments		(42)	(26)
Operating Segments
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		2,134	1,862
Adjusted EBITDA		1,393	1,352
Operating Segments | L&S
Segment Reporting Information [Line Items]
Operating Lease, Lease Income		175	249
Income from equity method investments		52	36
Other income		12	15
Total segment revenues and other income	[1]	(1,337)	(1,294)
Adjusted EBITDA	[2]	904	896
Capital Expenditure		77	59
Operating Segments | G&P
Segment Reporting Information [Line Items]
Operating Lease, Lease Income		81	92
Income from equity method investments		47	34
Other income		(2)	14
Total segment revenues and other income	[1]	(1,273)	(1,045)
Adjusted EBITDA	[2]	489	456
Capital Expenditure		95	30
Service [Member]
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		554	589
Service [Member] | L&S
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		72	84
Service [Member] | G&P
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		482	505
Service [Member] | Operating Segments | L&S
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		983	953
Service [Member] | Operating Segments | G&P
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		486	508
Product [Member]
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		497	282
Product [Member] | L&S
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		1	1
Product [Member] | G&P
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		496	281
Product [Member] | Operating Segments | L&S
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		4	4
Product [Member] | Operating Segments | G&P
Segment Reporting Information [Line Items]
Total revenues from contracts with customers		661	397
Third Party [Member] | L&S
Segment Reporting Information [Line Items]
Total segment revenues and other income		(135)	(129)
Third Party [Member] | G&P
Segment Reporting Information [Line Items]
Total segment revenues and other income		$ (1,212)	$ (989)
[1]	Within the total segment revenues and other income amounts presented above, third party revenues for the L&S segment were $135 million and $129 million for the three months ended March 31, 2022 and March 31, 2021, respectively. Third party revenues for the G&P segment were $1,212 million and $989 million for the three months ended March 31, 2022 and March 31, 2021, respectively.
[2]	See below for the reconciliation from Segment Adjusted EBITDA to “Net income.”

Segment Information - Reconcili

Segment Information - Reconciliation to Net Income (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2022	Mar. 31, 2021
Segment Reporting, Revenue Reconciling Item [Line Items]
Cost, Depreciation and Amortization	[1]	$ (313)	$ (329)
Interest and Other Financial Costs		(222)	(225)
Income from equity method investments		99	70
Proceeds from Equity Method Investment, Distribution		(120)	(119)
Other Cost and Expense, Operating		(1)	(9)
Net income		833	748
Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted EBITDA		1,393	1,352
Segment Reconciling Items [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Proceeds from Equity Method Investment, Distribution		(132)	(121)
Adjusted EBITDA attributable to noncontrolling interests		9	10
L&S
Segment Reporting, Revenue Reconciling Item [Line Items]
Cost, Depreciation and Amortization		(130)	(147)
L&S | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted EBITDA	[2]	904	896
Income from equity method investments		52	36
G&P
Segment Reporting, Revenue Reconciling Item [Line Items]
Cost, Depreciation and Amortization		(183)	(182)
G&P | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted EBITDA	[2]	489	456
Income from equity method investments		$ 47	$ 34
[1]	Depreciation and amortization attributable to L&S was $130 million and $147 million for the three months ended March 31, 2022 and March 31, 2021, respectively. Depreciation and amortization attributable to G&P was $183 million and $182 million for the three months ended March 31, 2022 and March 31, 2021, respectively.
[2]	See below for the reconciliation from Segment Adjusted EBITDA to “Net income.”

Property, Plant and Equipment_2

Property, Plant and Equipment (Summary of Property, Plant and Equipment) (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 26,691	$ 26,546
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	6,779	6,504
Property, Plant and Equipment, Net, Total	19,912	20,042
L&S
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	12,438	12,371
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	3,347	3,227
Property, Plant and Equipment, Net, Total	9,091	9,144
G&P
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	14,253	14,175
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	3,432	3,277
Property, Plant and Equipment, Net, Total	$ 10,821	$ 10,898

Fair Value Measurements - Recur

Fair Value Measurements - Recurring - Financial Instruments by Valuation Hierarchy (Details) - USD ($) $ in Millions		Mar. 31, 2022	Dec. 31, 2021
Commodity Contract [Member] | Not Designated as Hedging Instrument [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Asset	[1]	$ 0	$ 0
Derivative Liability, Fair Value, Gross Liability	[1]	(99)	(108)
Embedded Derivative Financial Instruments [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability		$ 99	$ 108
[1]	Includes the embedded derivative in the commodity contract discussed above.

Fair Value Measurments - Recurr

Fair Value Measurments - Recurring - Significant Unobservable Inputs in Level 3 Valuation (Details)	3 Months Ended
	Mar. 31, 2022USD ($)$ / gal
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Derivative, Average Forward Price | $ / gal	0.97
Embedded Derivative Financial Instruments [Member] | Natural Gas [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Embedded Derivative Renewal Term	5 years
Fair Value, Inputs, Level 3 [Member] | Embedded Derivative Financial Instruments [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Probability of Renewal	100.00%
Minimum [Member] | Fair Value, Inputs, Level 3 [Member] | Commodity Contract [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Forward Commodity Price	$ 0.73
Maximum [Member] | Fair Value, Inputs, Level 3 [Member] | Commodity Contract [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Forward Commodity Price	$ 2.38

Fair Value Measurements - Rec_2

Fair Value Measurements - Recurring - Changes in Level 3 Measurements (Details) - Embedded Derivatives in Commodity Contracts (net) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2022	Mar. 31, 2021
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value at beginning of period		$ (108)	$ (63)
Total gains (losses) (realized and unrealized) included in earnings	[1]	4	(6)
Settlements		5	3
Fair value at end of period		(99)	(66)
The amount of total gains (losses) for the period included in earnings attributable to the change in unrealized losses relating to liabilities still held at end of period		$ 5	$ (5)
[1]	Gain/(loss) on derivatives embedded in commodity contracts are recorded in “Purchased product costs” on the Consolidated Statements of Income.

Fair Value Measurements - Repor

Fair Value Measurements - Reported (Details) - USD ($) $ in Millions		Mar. 31, 2022	Dec. 31, 2021
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	[1]	$ 19,864	$ 18,664
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	[1]	$ 20,392	$ 20,779
[1]	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” on the Consolidated Balance Sheets.

Derivative Financial Instrume_3

Derivative Financial Instruments - Embedded Derivatives in Commodity Contracts (Details) - Embedded Derivative Financial Instruments [Member] $ in Millions	3 Months Ended
	Mar. 31, 2022USD ($)	Dec. 31, 2021USD ($)
Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member]
Derivative [Line Items]
Derivative Liability	$ (99)	$ (108)
Natural Gas [Member]
Derivative [Line Items]
Number of Renewals	1
Embedded Derivative Renewal Term	5 years

Derivative Financial Instrume_4

Derivative Financial Instruments - Derivatives Balance Sheet Location (Details) - Not Designated as Hedging Instrument [Member] - Commodity Contract [Member] - USD ($) $ in Millions		Mar. 31, 2022	Dec. 31, 2021
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	[1]	$ 0	$ 0
Derivative Liability, Fair Value, Gross Liability	[1]	99	108
Other current assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	[1]	0	0
Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	[1]	16	15
Other noncurrent assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	[1]	0	0
Other Noncurrent Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	[1]	$ 83	$ 93
[1]	Includes the embedded derivative in the commodity contract discussed above.

Derivatives Financial Instrumen

Derivatives Financial Instruments - Derivative Income Statement Location (Details) - Purchased product costs - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Derivative [Line Items]
Realized gain (loss)	$ (5)	$ (3)
Total gain (loss)	4	(6)
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	$ 9	$ (3)

Debt - Summary of Outstanding B

Debt - Summary of Outstanding Borrowings (Detail) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Total	$ 20,108	$ 18,909
Unamortized debt issuance costs	(116)	(102)
Unamortized discount/premium	(236)	(236)
Long-term Debt and Lease Obligation, Current	999	499
Total long-term debt due after one year	18,757	18,072
Fixed Rate Senior Notes [Member] | MPLX LP [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	20,032	18,532
Fixed Rate Senior Notes [Member] | MarkWest [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	23	23
Fixed Rate Senior Notes [Member] | ANDX LP [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	45	45
Finance Lease [Member] | MPLX LP [Member]
Debt Instrument [Line Items]
Financing lease obligations	8	9
MPLX Revolving Credit Facility due July 2024 [Member]
Debt Instrument [Line Items]
Long-term Line of Credit	$ 0	$ 300
Senior Note Due March 2052 [Domain] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.95%
Percent of Par	98.982%
Minimum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	1.75%
Maximum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.50%

Debt - Additional Information (

Debt - Additional Information (Detail) - USD ($) $ in Millions	Mar. 14, 2022	Mar. 31, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Debt and Lease Obligation		$ 20,108	$ 18,909
Unamortized Debt Issuance Expense		116	102
Debt Instrument, Unamortized Discount		236	236
Long-term debt		18,757	18,072
MPLX Revolving Credit Facility due July 2024 [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity		3,500
Long-term Line of Credit		0	300
MPLX Revolving Credit Facility due July 2024 [Member] | MPLX LP [Member]
Debt Instrument [Line Items]
Proceeds from Lines of Credit		$ 900
Debt Instrument, Interest Rate, Effective Percentage		1.451%
Repayments of Long-term Lines of Credit		$ 1,200
Letters of Credit Outstanding		1
Line of Credit Facility, Remaining Borrowing Capacity		$ 3,500
Line of Credit Facility, Remaining Borrowing Capacity, Percentage		100.00%
Fixed Rate Senior Notes [Member] | MPLX LP [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 20,032	18,532
Fixed Rate Senior Notes [Member] | ANDX LP [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		45	45
Fixed Rate Senior Notes [Member] | MarkWest [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		23	23
Finance Lease [Member] | MPLX LP [Member]
Debt Instrument [Line Items]
Finance Lease, Liability		$ 8	$ 9
Senior Notes [Member] | Senior Note Due March 2052 [Domain]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		4.95%
Percent of Par		98.982%
Debt Instrument, Face Amount		$ 1,500
Debt Instrument, Issuance Date	Mar. 14, 2022
Minimum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		1.75%
Maximum [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		5.50%

Revenue Disaggregation of Reven

Revenue Disaggregation of Revenue (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2022	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Product and Service [Extensible Enumeration]		Product and Service, Other [Member]	Product and Service, Other [Member]
Revenue Not from Contract with Customer, Other	[1]	$ 476	$ 477
Revenues		2,610	2,339
Operating Segments
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		2,134	1,862
L&S
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		$ 987	$ 957
Revenue from Contract with Customer, Product and Service [Extensible Enumeration]		Product and Service, Other [Member]	Product and Service, Other [Member]
L&S | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	[2]	$ 1,337	$ 1,294
G&P
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		$ 1,147	$ 905
Revenue from Contract with Customer, Product and Service [Extensible Enumeration]		Product and Service, Other [Member]	Product and Service, Other [Member]
G&P | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	[2]	$ 1,273	$ 1,045
Service [Member]
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		554	589
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		915	872
Service [Member] | L&S
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		72	84
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		911	869
Service [Member] | L&S | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		983	953
Service [Member] | G&P
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		482	505
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		4	3
Service [Member] | G&P | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		486	508
Service, Other [Member]
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		123	77
Service, Other [Member] | L&S
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		0	0
Service, Other [Member] | G&P
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		123	77
Product [Member]
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		497	282
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		45	42
Product [Member] | L&S
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		1	1
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		3	3
Product [Member] | L&S | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		4	4
Product [Member] | G&P
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		496	281
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		42	39
Product [Member] | G&P | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		$ 661	$ 397
[1]	Non-ASC 606 Revenue includes rental income, sales-type lease revenue, income from equity method investments, and other income.
[2]	Within the total segment revenues and other income amounts presented above, third party revenues for the L&S segment were $135 million and $129 million for the three months ended March 31, 2022 and March 31, 2021, respectively. Third party revenues for the G&P segment were $1,212 million and $989 million for the three months ended March 31, 2022 and March 31, 2021, respectively.

Revenue Contract Balances (Deta

Revenue Contract Balances (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021	[1]	Dec. 31, 2020
Long-term deferred revenue, beginning balance		$ 383
Long-term deferred revenue, ending balance		405
Liability, change in timeframe, performance obligation satisfied, revenue recognized		0	$ 0
Contract Liability, Noncurrent, Period Increase (Decrease)		0	0
ASC 606
Contract assets, beginning balance	[1]	25	40
Contract assets, additions/(deletions)		(18)	(27)
Contract assets, revenue recognized	[2]	0	0
Contract assets, ending balance		7	13
Contract With Customer Non Current Asset Reclassified To Receivable [Line Items]		0	0
Contract with Customer, Asset, before Allowance for Credit Loss, Noncurrent		2	2	$ 2		$ 2
Deferred revenue, beginning balance	[1]	56	37
Deferred revenue, additions/(deletions)		11	7
Deferred revenue, revenue recognized	[2]	(9)	(1)
Deferred revenue, ending balance		58	43
Deferred revenue - related parties, beginning balance	[1]	60	91
Deferred revenue - related party, additions/(deletions)		34	21
Deferred revenue - related parties, revenue recognized	[2]	(26)	(20)
Deferred revenue - related parties, ending balance		68	92
Long-term deferred revenue, beginning balance	[1]	135	119
Long-term deferred revenue, additions/(deletions)		2	4
Long-term deferred revenue, revenue recognized	[2]	0	0
Long-term deferred revenue, ending balance		137	123
Long-term deferred revenue - related parties, beginning balance	[1]	31	48
Long-term deferred revenue - related party, additions/(deletions)		0	(4)
Long-term deferred revenue - related parties, revenue recognized	[2]	0	0
Long-term deferred revenue - related parties, ending balance		31	44
Contract Liability, Noncurrent, Revenue Recognized		0	0
Contract with Customer, Liability, Noncurrent		5	6	$ 5		$ 6
Contract with Customer, Asset Increase (Decrease), Noncurrent		$ 0	$ 0
[1]	Balance represents ASC 606 portion of each respective line item.
[2]	No significant revenue was recognized related to past performance obligations in the current periods.

Revenue Remaining Performance O

Revenue Remaining Performance Obligations (Details) $ in Millions	Mar. 31, 2022USD ($)
Revenue from Contract with Customer [Abstract]
Contract with customer, liability	$ 293
Revenue, Remaining Performance Obligation, Amount	9,758	[1],[2],[3]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-04-01
Revenue from Contract with Customer [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 1,432
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, expected timing of satisfaction, years	9 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue from Contract with Customer [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 1,771
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, expected timing of satisfaction, years	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue from Contract with Customer [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 1,633
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, expected timing of satisfaction, years	2 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01
Revenue from Contract with Customer [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 1,560
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, expected timing of satisfaction, years	3 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01
Revenue from Contract with Customer [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 3,362
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, expected timing of satisfaction, years	4 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2043-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, expected timing of satisfaction, years	22 years
[1]	All fixed consideration from contracts with customers is included in the amounts presented above. Variable consideration that is constrained or not required to be estimated as it reflects our efforts to perform is excluded.
[2]	Arrangements deemed implicit leases and sales-type leases are excluded from this table.
[3]	Only minimum volume commitments that are deemed fixed are included in the table above. MPLX has various minimum volume commitments in processing arrangements that vary based on the actual Btu content of the gas received. These amounts are deemed variable consideration and are excluded from the table above.

Supplemental Cash Flow Inform_3

Supplemental Cash Flow Information - Summary of Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Supplemental Cash Flow Information [Abstract]
Interest Paid, Excluding Capitalized Interest, Operating Activities	$ 213	$ 231

Supplemental Cash Flow Inform_4

Supplemental Cash Flow Information - Summary of Reconciliation of Additions to Property, Plant and Equipment to Total Capital Expenditures (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Supplemental Cash Flow Elements [Abstract]
Increase/(decrease) in capital accruals	$ 3	$ (37)

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2021
Commitments And Contingencies [Line Items]
Accrued liabilities for environmental remediation	$ 42			$ 23
Loss Contingency, Damages Sought, Value			$ 187
Loss Contingency, Damages Paid, Value		$ 4
Guarantor Obligations, Origin and Purpose	GuaranteesOver the years, MPLX has sold various assets in the normal course of its business. Certain of the related agreements contain performance and general guarantees, including guarantees regarding inaccuracies in representations, warranties, covenants and agreements, and environmental and general indemnifications that require MPLX to perform upon the occurrence of a triggering event or condition. These guarantees and indemnifications are part of the normal course of selling assets. MPLX is typically not able to calculate the maximum potential amount of future payments that could be made under such contractual provisions because of the variability inherent in the guarantees and indemnities. Most often, the nature of the guarantees and indemnities is such that there is no appropriate method for quantifying the exposure because the underlying triggering event has little or no past experience upon which a reasonable prediction of the outcome can be based.We hold a 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 referred to as the Bakken Pipeline system or DAPL. In 2020, the U.S. District Court for the District of Columbia (the “D.D.C.”) ordered the U.S. 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 EIS is currently expected to be completed in the second half of 2022.In May 2021, the D.D.C. denied a renewed request for an injunction to shut down the pipeline while the EIS is being prepared. In June 2021, the D.D.C. issued an order dismissing without prejudice the tribes’ claims against the Dakota Access Pipeline. The litigation could be reopened or new litigation challenging the EIS, once completed, could be filed. The pipeline remains operational.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 pipeline were temporarily shut down, 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 shutdown. MPLX also expects to contribute its 9.19 percent pro rata share of any costs to remediate any deficiencies to reinstate the permit and/or return the pipeline into operation. If the vacatur of the easement permit 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, 2022, our maximum potential undiscounted payments under the Contingent Equity Contribution Agreement were approximately $170 million.
Indirect Ownership Interest [Member] | Bakken Pipeline System [Member]
Commitments And Contingencies [Line Items]
Equity method investment, ownership percentage	9.19%
Guarantee Type, Other [Member]
Commitments And Contingencies [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 170