MPLX (MPLX) 10-K 24 Feb 22 2021 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2021	Feb. 15, 2022	Jun. 30, 2021
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
Document Transition Report	false
Entity File Number	001-35714
Entity Registrant Name	MPLX LP
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	27-0005456
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	45840-3229
City Area Code	419
Local Phone Number	421-2414
Title of 12(b) Security	Common Units Representing Limited Partnership Interests
Trading Symbol	MPLX
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 11.2
Entity Common Stock, Shares Outstanding		1,014,627,674
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Entity Central Index Key	0001552000
Current Fiscal Year End Date	--12-31

Audit Information

Audit Information	12 Months Ended
	Dec. 31, 2021
Auditor Information [Abstract]
Auditor Firm ID	238
Auditor Name	PricewaterhouseCoopers LLP
Auditor Location	Toledo, Ohio

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenues and other income:
Operating Lease, Lease Income, Related Party	$ 743	$ 952	$ 1,196
Income (Loss) from Equity Method Investments	321	(936)	290
Other Income	21	5	12
Related Party Transaction, Other Revenues from Transactions with Related Party	110	102	107
Revenues, Total	10,027	7,569	9,041
Costs and expenses:
Purchases from related parties	1,219	1,116	1,231
Cost, Depreciation and Amortization	1,287	1,377	1,254
Goodwill and Intangible Asset Impairment	42	2,165	1,197
General and Administrative Expense	353	378	388
Restructuring Charges	0	37	0
Taxes, Miscellaneous	120	125	113
Costs and Expenses, Total	6,035	7,358	6,664
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent, Total	3,992	211	2,377
Interest And Other Financial Costs From Related Parties	8	5	11
Interest expense	785	829	851
Other Nonoperating Income (Expense)	86	62	53
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest, Total	3,113	(685)	1,462
Income Tax Expense (Benefit)	1	2	0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Total	3,112	(687)	1,462
Net Income (Loss) Attributable to Noncontrolling Interest	35	33	28
Income (Loss) Attributable to Predecessor	0	0	401
Net Income (Loss) Attributable to Parent, Total	3,077	(720)	1,033
Net Income (Loss) Allocated to Limited Partners	$ 2,936	$ (842)	$ 935
Limited Partners' Capital Account [Abstract]
Common - basic (in units)	1,027	1,051	906
Common - diluted (in units)	1,027	1,051	907
Rental cost of sales
Costs and expenses:
Labor and Related Expense	$ 136	$ 135	$ 141
Third Party
Revenues and other income:
Operating Lease, Lease Income	376	398	388
Sales-type Lease, Revenue	0	0	0
Marathon Petroleum Corporation [Member]
Revenues and other income:
Sales-type Lease, Revenue	435	152	7
Costs and expenses:
Labor and Related Expense		254
Restructuring Charges	0	37
Marathon Petroleum Corporation [Member] | Rental cost of sales - related parties [Member]
Costs and expenses:
Labor and Related Expense	$ 109	$ 160	$ 165
Limited Partners Common Units
Net Income Attributable To Parent Company Per Limited Partner Unit Basic And Diluted [Abstract]
Common - basic (in USD per unit)	$ 2.86	$ (0.80)	$ 1
Common - diluted (in USD per unit)	$ 2.86	$ (0.80)	$ 1
Limited Partners' Capital Account [Abstract]
Common - basic (in units)	1,027	1,051	906
Common - diluted (in units)	1,027	1,051	907
Service [Member]
Revenues and other income:
Revenue from Contract with Customer, Excluding Assessed Tax	$ 2,313	$ 2,397	$ 2,498
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties	3,628	3,580	3,455
Product [Member]
Revenues and other income:
Revenue from Contract with Customer, Excluding Assessed Tax	1,590	636	806
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties	145	128	142
Oil and Gas, Refining and Marketing [Member]
Costs and expenses:
Cost of Goods and Services Sold	1,184	1,326	1,489
Natural Gas, Midstream [Member]
Costs and expenses:
Cost of Goods and Services Sold	1,585	539	686
Service, Other [Member]
Revenues and other income:
Revenue from Contract with Customer, Excluding Assessed Tax	345	155	140
Series A Preferred Stock [Member] | Preferred Partner [Member]
Costs and expenses:
Net Income (Loss) Attributable to Parent, Total	100	81	81
Dividends, Preferred Stock	100	81	81
Series B Preferred Stock [Member] | Preferred Partner [Member]
Costs and expenses:
Net Income (Loss) Attributable to Parent, Total	41	41	42
Dividends, Preferred Stock	$ 41	$ 41	$ 17

Consolidated Statements of In_2

Consolidated Statements of Income (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Interest costs capitalized	$ 14	$ 39	$ 51

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income Statement - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Statement of Comprehensive Income [Abstract]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 3,112	$ (687)	$ 1,462
Other comprehensive income/(loss), net of tax:
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Adjustment, Net of Tax	(2)	0	1
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest, Total	3,110	(687)	1,463
Less comprehensive income attributable to:
Net Income (Loss) Attributable to Noncontrolling Interest	35	33	28
Comprehensive Income (loss), Net of Tax, Attributable to Predecessor	0	0	401
Comprehensive Income (Loss), Net of Tax, Attributable to Parent, Total	$ 3,075	$ (720)	$ 1,034

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Assets, Current [Abstract]
Cash and Cash Equivalents, at Carrying Value	$ 13	$ 15
Accounts Receivable, after Allowance for Credit Loss, Current	654	452
Due from Related Parties, Current	644	677
Inventory, Gross	142	118
Disposal Group, Including Discontinued Operation, Assets, Current	0	188
Assets, Current, Total	1,507	1,515
Equity Method Investments	3,981	4,036
Property, Plant and Equipment, Net	20,042	21,218
Intangible Assets, Net (Excluding Goodwill)	831	959
Goodwill	7,657	7,657
Due from Related Parties, Noncurrent	1,161	672
Other Assets, Noncurrent	60	48
Assets, Total	35,507	36,414
Current liabilities:
Accounts Payable, Current	172	152
Accrued Liabilities, Current	363	194
Due to Related Parties, Current	1,780	356
Accrued Property Plant and Equipment Current	97	84
Debt, Current	499	764
Interest Payable	202	222
Other Liabilities, Current	176	150
Disposal Group, Including Discontinued Operation, Liabilities, Current	0	101
Total current liabilities	3,348	2,086
Deferred Revenue, Noncurrent	383	314
Due to Related Parties, Noncurrent	302	283
Long-term Debt and Lease Obligation	18,072	19,375
Deferred Income Tax Liabilities, Net	10	12
Deferred Credits and Other Liabilities, Noncurrent	170	115
Total liabilities	22,490	22,429
Commitments and contingencies (see Note 21)
Series A preferred units	965	968
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]
Total MPLX LP partners’ capital	11,811	12,772
Noncontrolling interests	241	245
Total equity	12,052	13,017
Total liabilities, preferred units and equity	35,507	36,414
Third Party
Assets, Current [Abstract]
Other Assets, Current	54	65
Operating Lease, Right-of-Use Asset	268	309
Current liabilities:
Operating Lease, Liability, Current	59	63
Operating Lease, Liability, Noncurrent	205	244
Marathon Petroleum Corporation [Member]
Assets, Current [Abstract]
Other Assets, Current	3	1
Operating Lease, Right-of-Use Asset	229	231
Limited Partners Common Units | Public
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]
Limited Partners' Capital Account	8,579	9,384
Limited Partners Common Units | Marathon Petroleum Corporation [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]
Limited Partners' Capital Account	2,638	2,792
Series B Preferred Stock [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]
Preferred Units, Preferred Partners' Capital Accounts	611	611
LOOP and Explorer
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]
Accumulated other comprehensive loss	$ (17)	$ (15)

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - shares	Dec. 31, 2021	Dec. 31, 2020
Limited Partners Common Units | Public
Units issued	369,000,000	391,000,000
Units outstanding	369,000,000	391,000,000
Limited Partners Common Units | Marathon Petroleum Corporation [Member]
Units issued	647,000,000	647,000,000
Units outstanding	647,415,452	647,000,000
Series B Preferred Stock [Member]
Units issued	600,000	600,000
Units outstanding	600,000	600,000

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating activities:
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 3,112	$ (687)	$ 1,462
Adjustments to reconcile net income/(loss) to net cash provided by operating activities:
Amortization of deferred financing costs	70	61	42
Cost, Depreciation and Amortization	1,287	1,377	1,254
Goodwill and Intangible Asset Impairment	42	2,165	1,197
Deferred income taxes	(2)	(1)	(2)
Asset retirement expenditures	0	0	(1)
(Gain)/loss on disposal of assets	(13)	4	(6)
Income (Loss) from Equity Method Investments	(321)	936	(290)
Distributions from unconsolidated affiliates	508	459	525
Changes in:
Current receivables	(199)	62	17
Inventories	(24)	(12)	(9)
Fair value of derivatives	45	3	2
Current accounts payable and accrued liabilities	193	36	(59)
Current assets/current liabilities - related parties	101	8	(163)
Increase (Decrease) in Other Operating Assets and Liabilities, Net	(2)	(5)	4
Deferred revenue	88	112	100
All other, net	26	3	9
Net cash provided by operating activities	4,911	4,521	4,082
Investing activities:
Additions to property, plant and equipment	(529)	(1,183)	(2,408)
Proceeds from Previous Acquisition	0	0	6
Disposal of assets	126	56	30
Investments in unconsolidated affiliates	(151)	(266)	(713)
Distributions from unconsolidated affiliates - return of capital	36	123	18
All other, net	0	8	4
Net cash used in investing activities	(518)	(1,262)	(3,063)
Financing activities:
Proceeds from long-term lines of credit	4,175	6,810	9,174
Repayments of Debt	5,821	6,414	7,924
Related party debt - borrowings	8,493	6,264	9,313
Related party debt - repayments	(7,043)	(6,858)	(8,719)
Debt issuance costs	0	(25)	(20)
Payments for Repurchase of Common Stock	(630)	(33)	0
Distributions to unitholders and general partner	(3,432)	(2,884)	(2,435)
Distributions to noncontrolling interests	(39)	(37)	(30)
Contributions from MPC	45	50	74
Proceeds from Noncontrolling Interests	0	0	95
All other, net	(2)	(10)	(13)
Net Cash Provided by (Used in) Financing Activities	(4,395)	(3,259)	(1,089)
Net (decrease)/increase in cash, cash equivalents and restricted cash	(2)	0	(70)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Beginning Balance	15	15	85
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Ending Balance	13	15	15
Series A Preferred Stock [Member] | Preferred Partner [Member]
Financing activities:
Distributions to Series A preferred unitholders	(100)	(81)	(81)
Series B Preferred Stock [Member] | Preferred Partner [Member]
Financing activities:
Distributions to Series A preferred unitholders	(41)	(41)	(21)
Payments of Distributions on Preferred Units from Predecessor	$ 0	$ 0	$ (502)

Consolidated Statements of Equi

Consolidated Statements of Equity - USD ($) $ in Millions	Total	Series A Convertible Preferred Units	LOOP and Explorer	Series B Preferred Stock [Member]	Series A Preferred Stock [Member]	PublicLimited Partners Common Units	Marathon Petroleum Corporation [Member]	Marathon Petroleum Corporation [Member]Limited Partners Common Units	AOCI Attributable to Parent	Noncontrolling Interest	Equity of PredecessorMarathon Petroleum Corporation [Member]
Other Ownership Interests, Capital Account							$ 10,867
Limited Partners' Capital Account						$ 8,336		$ (1,612)
Preferred Units, Preferred Partners' Capital Accounts				$ 0
Accumulated other comprehensive loss			$ (16)
Noncontrolling interests	$ 156
Series A preferred units					$ 1,004
Beginning balance at Dec. 31, 2018	17,731
Stockholders' Equity, Other	13			0		12		0	$ 1	$ 0	$ 0
Net income (loss)	(1,381)			(17)		(340)		(595)	0	(28)	(401)
Allocation of MPC's net investment at acquisition	0			(615)		(2,983)		(7,199)	0	0	10,797
Partners' Capital Account, Distributions	(2,989)			(21)	(81)	(907)		(1,529)	0	(30)	(502)
Partners' Capital Account, Contributions	441			0		0		315	0	95	31
Unit conversion	36			0	(36)	36		0	0	0	0
Ending balance at Dec. 31, 2019	16,613
Net income allocated					81
Other Ownership Interests, Capital Account							0
Limited Partners' Capital Account						10,800		4,968
Preferred Units, Preferred Partners' Capital Accounts				611
Accumulated other comprehensive loss			(15)
Noncontrolling interests	249
Series A preferred units					968
Stockholders' Equity, Other	5			0		6		(1)	0	0	0
Net income (loss)	768			(41)		307		535	0	(33)	0
Stock Repurchased and Retired During Period, Value	(33)			0		(33)		0	0	0	0
Allocation of MPC's net investment at acquisition	102			0		0		102	0	0	0
Partners' Capital Account, Distributions	(2,959)			(41)	(81)	(1,082)		(1,799)	0	(37)	0
Partners' Capital Account, Contributions	261			0		0		261	0	0	0
Ending balance at Dec. 31, 2020	13,017
Net income allocated					81
Other Ownership Interests, Capital Account							0
Limited Partners' Capital Account						9,384		2,792
Preferred Units, Preferred Partners' Capital Accounts				611
Accumulated other comprehensive loss			(15)
Noncontrolling interests	245
Series A preferred units	968	$ 968
Stockholders' Equity, Other	2			0		4		0	(2)	0	0
Net income (loss)	(3,012)			(41)		(1,087)		(1,849)	0	(35)	0
Stock Repurchased and Retired During Period, Value	(630)			0		(630)		0	0	0	0
Partners' Capital Account, Distributions	(3,512)			(41)	(100)	(1,269)		(2,163)	0	(39)	0
Partners' Capital Account, Contributions	160			0		0		160	0	0	0
Unit conversion	3			0	(3)	3		0	$ 0	$ 0	$ 0
Ending balance at Dec. 31, 2021	12,052
Net income allocated					$ 100
Other Ownership Interests, Capital Account							$ 0
Limited Partners' Capital Account						$ 8,579		$ 2,638
Preferred Units, Preferred Partners' Capital Accounts				$ 611
Accumulated other comprehensive loss			$ (17)
Noncontrolling interests	241
Series A preferred units	$ 965	$ 965

Description of Business and Bas

Description of Business and Basis of Presentation	12 Months Ended
	Dec. 31, 2021
Limited Liability Company or Limited Partnership, Business Organization and Operations [Abstract]
Business Description and Basis of Presentation	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 (“MPC”) 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 was formed on March 27, 2012 as a Delaware limited partnership and completed its initial public offering on October 31, 2012. 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 10 for additional information regarding the operations and results of these segments. On July 31, 2020, MPLX completed the exchange of Western Refining Wholesale, LLC (WRW”) to Western Refining Southwest, Inc. (now known as Western Refining Southwest LLC) (“WRSW”), a wholly owned subsidiary of MPC, in exchange for the redemption of 18,582,088 MPLX common units held by WRSW (the “Wholesale Exchange”). See Note 4 for additional information regarding the Wholesale Exchange. These financial statements include the results of WRSW through July 31, 2020. On July 30, 2019, MPLX completed its acquisition of Andeavor Logistics LP (“ANDX” and such acquisition, the “Merger”). At the effective time of the Merger, each common unit held by ANDX’s public unitholders was converted into the right to receive 1.135 MPLX common units. ANDX common units held by certain affiliates of MPC were converted into the right to receive 1.0328 MPLX common units. See Note 4 for additional information regarding the Merger. Basis of Presentation – The accompanying consolidated financial statements of MPLX have been prepared in accordance with GAAP. The 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 a VIE in which MPLX exercises significant influence but does not control and is not the primary beneficiary are also accounted for using the equity method. In relation to the Merger described above and in Note 4, ANDX’s assets, liabilities and results of operations prior to the Merger are collectively included in what we refer to as the “Predecessor” from October 1, 2018, which was the date that MPC acquired Andeavor. MPLX’s acquisition of ANDX is considered a transfer between entities under common control due to MPC’s relationship with ANDX prior to the Merger. As an entity under common control with MPC, MPLX recorded the assets acquired and liabilities assumed on its consolidated balance sheets at MPC’s historical carrying value. For the acquiring entity, transfers of businesses between entities under common control require prior periods to be retrospectively adjusted for those dates that the entity was under common control. Accordingly, the accompanying financial statements and related notes of MPLX LP have been retrospectively adjusted to include the historical results of ANDX beginning October 1, 2018.

Summary of Principal Accounting

Summary of Principal Accounting Policies	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Significant Accounting Policies [Text Block]	Summary of Principal Accounting Policies Use of Estimates – The preparation of financial statements in accordance with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amounts of revenues and expenses during the respective reporting periods. Actual results could differ materially from those estimates. Estimates are subject to uncertainties due to the levels of subjectivity and judgment necessary to account for highly uncertain matters or the susceptibility of such matters to change and affect items such as valuing identified intangible assets; determining the fair value of derivative instruments; evaluating impairments of long-lived assets, goodwill and equity investments; establishing estimated useful lives for long-lived assets; acquisition accounting; estimating revenues, expense accruals and capital expenditures; valuing AROs; recognizing share-based compensation expense; and determining liabilities, if any, for environmental and legal contingencies. Revenue Recognition – Revenue is measured based on consideration specified in a contract with a customer. MPLX recognizes revenue when it satisfies a performance obligation by transferring control over a product or providing services to a customer. MPLX enters into a variety of contract types in order to generate “Product sales” and “Service revenue.” MPLX provides services under the following types of arrangements: • Fee-based arrangements – Under fee-based arrangements, MPLX receives a fee or fees for one or more of the following services: gathering, processing and transportation of natural gas; gathering, transportation, fractionation, exchange and storage of NGLs; and transportation, terminalling, storage and distribution of crude oil, refined products and other hydrocarbon-based products. The revenue MPLX earns from these arrangements is generally directly related to the volume of natural gas, NGLs, refined products or crude oil that is handled by or flows through MPLX’s systems and facilities and is not normally directly dependent on commodity prices. In certain cases, MPLX’s arrangements provide for minimum volume commitments. • Fee-based arrangements are reported as “Service revenue” on the Consolidated Statements of Income. Revenue is recognized over time as services are performed. In certain instances when specifically stated in the contract terms, MPLX purchases product after fee-based services have been provided. Revenue from the sale of products purchased after services are provided is reported as “Product sales” on the Consolidated Statements of Income and recognized on a gross basis, as MPLX takes control of the product and is the principal in the transaction. • Percent-of-proceeds arrangements – Under percent-of-proceeds arrangements, MPLX gathers and processes natural gas on behalf of producers; sells the resulting residue gas, condensate and NGLs at market prices; and remits to producers an agreed-upon percentage of the proceeds. In other cases, instead of remitting cash payments to the producer, MPLX delivers an agreed-upon percentage of the residue gas and NGLs to the producer (take-in-kind arrangements) and sells the volumes MPLX retains to third parties or related parties. Revenue is recognized on a net basis when MPLX acts as an agent and does not have control of the gross amount of gas and/or NGLs prior to it being sold. Percent-of-proceeds revenue is reported as “Service revenue - product related” on the Consolidated Statements of Income. • Keep-whole arrangements – Under keep-whole arrangements, MPLX gathers natural gas from the producer, processes the natural gas and sells the resulting condensate and NGLs to third parties at market prices. Because the extraction of the condensate and NGLs from the natural gas during processing reduces the Btu content of the natural gas, MPLX must either purchase natural gas at market prices for return to producers or make cash payment to the producers equal to the value of the energy content of this natural gas. Certain keep-whole arrangements also have provisions that require MPLX to share a percentage of the keep-whole profits with the producers based on the oil to gas ratio or the NGL to gas ratio. “Service revenue - product related” is recorded based on the value of the NGLs received on the date the services are performed. Natural gas purchased to return to the producer and shared NGL profits are recorded as a reduction of “Service revenue - product related” on the Consolidated Statements of Income on the date the services are performed. Sales of NGLs under these arrangements are reported as “Product sales” on the Consolidated Statements of Income and are reported on a gross basis as MPLX is the principal in the arrangement and controls the product prior to sale. The sale of the NGLs may occur shortly after services are performed at the tailgate of the plant, or after a period of time as determined by MPLX. • Purchase arrangements – Under purchase arrangements, MPLX purchases natural gas at either the wellhead or the tailgate of a plant. MPLX then gathers and delivers the natural gas to pipelines where MPLX may resell the natural gas. Wellhead purchase arrangements represent an arrangement with a supplier and are recorded in “Purchased product costs.” Often, MPLX earns fees for services performed prior to taking control of the product in these arrangements and “Service revenue” is recorded for these fees. Revenue generated from the sale of product obtained in tailgate purchase arrangements is reported as “Product sales” on the Consolidated Statements of Income and is recognized on a gross basis as MPLX purchases and takes control of the product prior to sale and is the principal in the transaction. In many cases, MPLX provides services under contracts that contain a combination of more than one of the arrangements described above. When fees are charged (in addition to product received) under percent-of-proceeds arrangements, keep-whole arrangements or purchase arrangements, MPLX records such fees as “Service revenue” on the Consolidated Statements of Income. The terms of MPLX’s contracts vary based on gas quality conditions, the competitive environment when the contracts are signed, and customer requirements. Performance obligations are determined based on the specific terms of the arrangements, economics of the geographical regions, and the services offered and whether they are deemed distinct. MPLX allocates the consideration earned between the performance obligations based on the stand-alone selling price when multiple performance obligations are identified. Revenue from MPLX’s service arrangements will generally be recognized over time as the performance obligation is satisfied as services are provided. MPLX has elected to use the output measure of progress to recognize revenue based on the units delivered, processed or transported. The transaction price has fixed components related to minimum volume commitments and variable components, which are primarily dependent on volumes. Variable consideration will generally not be estimated at contract inception as the transaction price is specifically allocable to the services provided each period. In instances in which tiered pricing structures do not reflect our efforts to perform, MPLX will estimate variable consideration at contract inception. “Product sales” will be recognized at a point in time when control of the product transfers to the customer. Minimum volume commitments may create contract liabilities or deferred credits if current period payments can be used for future services. Breakage is estimated and recognized into service revenue in instances where it is probable the customer will not use the credit in future periods. Amounts billed to customers for shipping and handling, electricity, and other costs to perform services are included in “Service revenue” on the Consolidated Statements of Income. Shipping and handling costs associated with product sales are included in “Purchased product costs” on the Consolidated Statements of Income. Facility expenses, costs of revenues and depreciation represent those expenses related to operating our various facilities and are necessary to provide both “Product sales” and “Service revenue.” Customers usually pay monthly based on the products purchased or services performed that month. Taxes collected from customers and remitted to the appropriate taxing authority are excluded from revenue. Based on the terms of certain natural gas gathering, transportation and processing agreements, MPLX is considered to be the lessor under several implicit operating lease arrangements in accordance with GAAP. Revenue and costs related to the portion of the revenue earned under these contracts considered to be implicit leases are recorded as “Rental income” and “Rental cost of sales,” respectively, on the Consolidated Statements of Income. Revenue and Expense Accruals – MPLX routinely makes accruals based on estimates for both revenues and expenses due to the timing of compiling billing information, receiving certain third-party information and reconciling MPLX’s records with those of third parties. The delayed information from third parties includes, among other things, actual volumes purchased, transported or sold, adjustments to inventory and invoices for purchases, actual natural gas and NGL deliveries, and other operating expenses. MPLX makes accruals to reflect estimates for these items based on its internal records and information from third parties. Estimated accruals are adjusted when actual information is received from third parties and MPLX’s internal records have been reconciled. Cash and Cash Equivalents – Cash and cash equivalents include cash on hand and on deposit and investments in highly liquid debt instruments with initial maturities of three months or less. Restricted Cash – Restricted cash consists of cash and investments that must be maintained as collateral for letters of credit issued to certain third-party producer customers. The balances will be outstanding until certain capital projects are completed and the third party releases the restriction. Restricted cash also consists of cash advances to be used for the operation and maintenance of an operated pipeline system. MPLX had no restricted cash as of the years ended December 31, 2021 or 2020. Receivables – Receivables primarily consist of customer accounts receivable, which are recorded at the invoiced amount and generally do not bear interest. Allowances for doubtful accounts are generally recorded when it becomes probable that the receivable will not be collected and are recorded to bad debt expense. We review the allowance quarterly with past-due balances over 90 days and other higher-risk amounts being reviewed individually for collectability. Balances that remain outstanding after reasonable collection efforts have been unsuccessful are written off through a charge to the valuation allowance and a credit to accounts receivable. Leases – As part of the adoption of ASU No. 2016-02, Leases (“ASC 842”), we elected the package of practical expedients permitted under the transition guidance within the new standard, which among other things, allowed us to grandfather the historical accounting conclusions until a reassessment event is present. We also elected the practical expedient to not recognize short-term leases on the balance sheet, the practical expedient related to right of way permits and land easements which allows us to carry forward our accounting treatment for those existing agreements, and the practical expedient to combine lease and non-lease components for the majority of our underlying classes of assets except for our third-party contractor service and equipment agreements and boat and barge equipment agreements in which we are the lessee. We did not elect the practical expedient to combine lease and non-lease components for arrangements in which we are the lessor. In instances where the practical expedient was not elected, lease and non-lease consideration is allocated based on relative standalone selling price. Right of use (“ROU”) assets represent our right to use an underlying asset in which we obtain substantially all of the economic benefits and the right to direct the use of the asset during the lease term. Lease liabilities represent our obligation to make lease payments arising from the lease. Operating lease ROU assets and lease liabilities are recognized at the commencement date based on the present value of lease payments over the lease term. We recognize ROU assets and lease liabilities on the balance sheet for leases with a lease term of greater than one year. Payments that are not fixed at the commencement of the lease are considered variable and are excluded from the ROU asset and lease liability calculations. In the measurement of our ROU assets and lease liabilities, the fixed lease payments in the agreement are discounted using a secured incremental borrowing rate for a term similar to the duration of the lease, as our leases do not provide implicit rates. Operating lease expense is recognized on a straight-line basis over the lease term. As a lessor under ASC 842, MPLX may be required to re-classify existing operating leases to sales-type leases upon modification and related reassessment of the leases. See Note 20 for further information regarding our ongoing evaluation of the impacts of lease reassessments as modifications occur. The net investment in a sales-type lease is recorded within “Current assets - related parties” and “Noncurrent assets - related parties” on the Consolidated Balance Sheets and is comprised of the present value of the sum of the future minimum lease payments representing the value of the lease receivable and the unguaranteed residual value of the leased assets. Management assesses the net investment in sales-type leases for recoverability quarterly. Inventories – Inventories consist of materials and supplies to be used in operations, line fill and other NGLs. Cost for materials and supplies are determined primarily using the weighted-average cost method. Inventories are valued at the lower of cost or market value. Imbalances – Within our pipelines and storage assets, we experience volume gains and losses due to pressure and temperature changes, evaporation and variances in meter readings and other measurement methods. Until settled, positive imbalances are recorded as other current assets and negative imbalances are recorded as accounts payable. Positive and negative product imbalances are settled in cash, settled by physical delivery of gas from a different source, or tracked and settled in the future. Property, Plant and Equipment – Property, plant and equipment are recorded at cost and depreciated on a straight-line basis over the estimated useful lives of the assets. Expenditures that extend the useful lives of assets are capitalized. Such assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. If the sum of the expected undiscounted future cash flows from the use of the asset and its eventual disposition is less than the carrying amount of the asset, an impairment assessment is performed and the excess of the book value over the fair value is recorded as an impairment loss. When items of property, plant and equipment are sold or otherwise disposed of, any gains or losses are reported on the Consolidated Statements of Income. Gains on the disposal of property, plant and equipment are recognized when they occur, which is generally at the time of closing. If a loss on disposal is expected, such losses are recognized when the assets are classified as held for sale. Interest costs for the construction or development of long-lived assets are capitalized and amortized over the related asset’s estimated useful life. Goodwill and Intangibles – Goodwill represents the excess of the purchase price over the estimated fair value of the net assets acquired in the acquisition of a business. Goodwill is not amortized, but rather is tested for impairment annually and when events or changes in circumstances indicate that the fair value of a reporting unit with goodwill has been reduced below carrying value. The impairment test requires allocating goodwill and other assets and liabilities to reporting units. The fair value of each reporting unit is determined using an income and/or market approach which is compared to the carrying value of the reporting unit. The fair value under the income approach is calculated using the expected present value of future cash flows method. Significant assumptions used in the cash flow forecasts include future operating performance, future volumes, discount rates, and future capital requirements. If the fair value of the reporting unit is less than the carrying value, including goodwill, the excess, if any, of the book value over the fair value of the reporting unit up to the amount of goodwill recorded is charged to net income as an impairment expense. See Note 14 for further details. Amortization of intangibles with definite lives is calculated using the straight-line method, which is reflective of the benefit pattern in which the estimated economic benefit is expected to be received over the estimated useful life of the intangible asset. Intangibles subject to amortization are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the intangible may not be recoverable. If the sum of the expected undiscounted future cash flows related to the asset is less than the carrying amount of the asset, an impairment loss is recognized based on the fair value of the asset. Other Taxes – Other taxes primarily include real estate taxes. Environmental Costs – Environmental expenditures are capitalized if the costs mitigate or prevent future contamination or if the costs improve environmental safety or efficiency of the existing assets. MPLX recognizes remediation costs and penalties when the responsibility to remediate is probable and the amount of associated costs can be reasonably estimated. The timing of remediation accruals coincides with completion of a feasibility study or the commitment to a formal plan of action. Remediation liabilities are accrued based on estimates of known environmental exposure and are discounted when the estimated amounts are reasonably fixed and determinable. If recoveries of remediation costs from third parties are probable, a receivable is recorded and is discounted when the estimated amount is reasonably fixed and determinable. Asset Retirement Obligations – An ARO is a legal obligation associated with the retirement of tangible long-lived assets that generally result from the acquisition, construction, development or normal operation of the asset. AROs are recorded at fair value in the period in which they are incurred, if a reasonable estimate of fair value can be made, and added to the carrying amount of the associated asset. This additional carrying amount is then depreciated over the life of the asset. The liability is determined using a credit adjusted risk free interest rate and increases due to the passage of time based on the time value of money until the obligation is settled. AROs have not been recognized for certain assets because the fair value cannot be reasonably estimated since the settlement dates of the obligations are indeterminate. Such obligations will be recognized in the period when sufficient information becomes available to estimate a range of potential settlement dates. At December 31, 2021, MPLX’s asset retirement obligation was $31 million, which is included on the balance sheet within “Deferred credits and other liabilities.” Investment in Unconsolidated Affiliates – Equity investments in which MPLX exercises significant influence, but does not control and is not the primary beneficiary, are accounted for using the equity method and are reported in “Equity method investments” on the accompanying Consolidated Balance Sheets. This includes entities in which we hold majority ownership but the minority shareholders have substantive participating rights. Differences in the basis of the investments and the separate net asset values of the investees, if any, are amortized into net income over the remaining useful lives of the underlying assets and liabilities, except for the excess related to goodwill. MPLX believes the equity method is an appropriate means for it to recognize increases or decreases measured by GAAP in the economic resources underlying the investments. Regular evaluation of these investments is appropriate to evaluate any potential need for impairment. MPLX uses evidence of a loss in value to identify if an investment has an other than a temporary decline. Impairments are recorded through “Income from equity method investments.” Derivative Instruments – MPLX may use commodity derivatives to economically hedge a portion of its exposure to commodity price risk. All derivative instruments (including derivatives embedded in other contracts) are recorded at fair value. Certain commodity derivatives are reflected on the consolidated balance sheets on a net basis by counterparty as they are governed by master netting arrangements. MPLX discloses the fair value of all derivative instruments under the captions “Other current assets” “Other noncurrent assets,” “Other current liabilities” and “Deferred credits and other liabilities” on the Consolidated Balance Sheets. Changes in the fair value of derivative instruments are reported on the Consolidated Statements of Income in accounts related to the item whose value or cash flows are being managed. All derivative instruments are marked to market through “Product sales,” “Purchased product costs,” or “Cost of revenues” on the Consolidated Statements of Income. Revenue gains and losses relate to contracts utilized to manage the cash flow for the sale of a product, typically NGLs. Purchased product costs gains and losses relate to contracts utilized to manage the cost of natural gas purchases, typically related to keep-whole arrangements. Cost of revenues gains and losses relate to a contract utilized to manage electricity costs. Changes in risk management for unrealized activities are reported as an adjustment to net income in computing cash flow from operating activities on the accompanying Consolidated Statements of Cash Flows. MPLX did not utilize any commodity derivatives during the years ended December 31, 2021, 2020 and 2019, and therefore did not elect hedge accounting. MPLX has historically elected the normal purchases and normal sales designation for certain contracts related to the physical purchase of electric power and the sale of some commodities. Fair Value Measurement – Financial assets and liabilities recorded at fair value in the Consolidated Balance Sheets are categorized based upon the fair value hierarchy established by GAAP, which classifies the inputs used to measure fair value into Level 1, Level 2 or Level 3. A financial instrument’s categorization within the valuation hierarchy is based upon the lowest level of input that is significant to the fair value measurement. The methods and assumptions utilized may produce a fair value that may not be realized in future periods upon settlement. Furthermore, while MPLX believes its valuation methods are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different estimate of fair value at the reporting date. For further discussion, see Note 15. Equity-Based Compensation Arrangements – MPLX issues phantom units under the MPLX LP 2018 Incentive Compensation Plan. A phantom unit entitles the grantee a right to receive a common unit upon the issuance of the phantom unit. The fair value of phantom unit awards granted to employees and non-employee directors is based on the fair market value of MPLX LP common units on the date of grant. The fair value of the units awarded is amortized into earnings using a straight-line amortization schedule over the period of service corresponding with the vesting period. For phantom units that vest immediately and are not forfeitable, equity-based compensation expense is recognized at the time of grant. MPLX previously issued performance units under the MPLX LP 2018 Incentive Compensation Plan. Performance units paying out in cash are accounted for as liability awards and recorded at fair value with a mark-to-market adjustment made each quarter. The performance units paying out in units are accounted for as equity awards. Equity-classified performance units with a market condition use a Monte Carlo valuation model to calculate a grant date fair value of market conditions. Equity-classified performance units with a performance condition are valued based on the grant date fair value of the payout deemed most probable to occur and is adjusted as the expectation for payout changes. To satisfy common unit awards, MPLX may issue new common units, acquire common units in the open market or use common units already owned by the general partner. Income Taxes – MPLX is not a taxable entity for United States federal income tax purposes or for the majority of the states that impose an income tax. Taxes on MPLX’s net income generally are borne by its partners through the allocation of taxable income. MPLX’s taxable income or loss, which may vary substantially from the net income or loss reported on the Consolidated Statements of Income, is includable in the federal income tax returns of each partner. MPLX and certain legal entities are, however, taxable entities under certain state jurisdictions. MPLX accounts for income taxes under the asset and liability method. Deferred income taxes are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax basis, capital loss carryforwards and net operating loss and credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates applied to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect of any tax rate change on deferred taxes is recognized as tax expense/(benefit) from continuing operations in the period that includes the enactment date of the tax rate change. Realizability of deferred tax assets is assessed and, if not more likely than not, a valuation allowance is recorded to reflect the deferred tax assets at net realizable value as determined by management. All deferred tax balances are classified as long-term in the accompanying Consolidated Balance Sheets. All changes in the tax bases of assets and liabilities are allocated among operations and items charged or credited directly to equity. Distributions – In preparing the Consolidated Statements of Equity, net income attributable to MPLX LP is allocated to Series A and Series B preferred unitholders based on a fixed distribution schedule, as discussed in Notes 7 and 9, and subsequently allocated to the general partner and limited partner unitholders. Distributions, although earned, are not accrued as a liability until declared. The allocation of net income attributable to MPLX LP for purposes of calculating net income per limited partner unit is described below. Net Income Per Limited Partner Unit – MPLX uses the two-class method when calculating the net income per unit applicable to limited partners, because there is more than one class of participating security. The classes of participating securities include common units, Series A and Series B preferred units and certain equity-based compensation awards. Net income attributable to MPLX LP is allocated to the unitholders differently for preparation of the Consolidated Statements of Equity and the calculation of net income per limited partner unit. In preparing the Consolidated Statements of Equity, net income attributable to MPLX LP is allocated to Series A and Series B preferred unitholders based on a fixed distribution schedule and subsequently allocated to remaining unitholders in accordance with their respective ownership percentages. The allocation of net income attributable to MPLX LP for purposes of calculating net income per limited partner unit is described in Note 8. In preparing net income per limited partner units, during periods in which a net loss attributable to MPLX is reported or periods in which the total distributions exceed the reported net income attributable to MPLX’s unitholders, the amount allocable to certain equity-based compensation awards is based on actual distributions to the equity-based compensation awards. Diluted earnings per unit is calculated by dividing net income attributable to MPLX’s common unitholders, after deducting amounts allocable to other participating securities, by the weighted average number of common units and potential common units outstanding during the period. Potential common units are excluded from the calculation of diluted earnings per unit during periods in which net income attributable to MPLX’s unitholders, after deducting amounts that are allocable to the outstanding equity-based compensation awards and preferred units, is a loss, as the impact would be anti-dilutive. Business Combinations – MPLX recognizes and measures the assets acquired and liabilities assumed in a business combination based on their estimated fair values at the acquisition date, with any remaining difference recorded as goodwill or gain from a bargain purchase. Depending on the nature of the transaction, management may engage an independent valuation specialist to assist with the determination of fair value of the assets acquired, liabilities assumed, noncontrolling interests, if any, and goodwill, based on recognized business valuation methodologies. If the initial accounting for the business combination is incomplete by the end of the reporting period in which the acquisition occurs, an estimate will be recorded. Subsequent to the acquisition, and not later than one year from the acquisition date, MPLX will record any material adjustments to the initial estimate based on new information obtained that would have existed as of the acquisition date. An adjustment that arises from information obtained that did not exist as of the date of the acquisition will be recorded in the period of the adjustment. An income, market or cost valuation method may be utilized to estimate the fair value of the assets acquired, liabilities assumed, and noncontrolling interests, if any, in a business combination. The income valuation method represents the present value of future cash flows over the life of the asset using: (i) discrete financial forecasts, which rely on management’s estimates of volumes, certain commodity prices, revenue and operating expenses; (ii) long-term growth rates; and (iii) appropriate discount rates. The market valuation method uses prices paid for a reasonably similar asset by other purchasers in the market, with adjustments relating to any differences between the assets. The cost valuation method is based on the replacement cost of a comparable asset at prices at the time of the acquisition reduced for depreciation of the asset. Acquisition-related costs are expensed as incurred in connection with each business combination. Acquisitions in which the company or business being acquired by MPLX had an existing relationship with MPC may result in the transaction being considered a transfer between entities under common control. In this situations, MPLX records the assets acquired and liabilities assumed on its consolidated balance sheets at MPC’s historical carrying value. For the acquiring entity, transfers of businesses between entities under common control require prior periods to be retrospectively adjusted for those dates that the entity was under common control. See Note 4 for more information about the acquisitions.

Accounting Standards

Accounting Standards	12 Months Ended
	Dec. 31, 2021
Accounting Standards Update and Change in Accounting Principle [Abstract]
Accounting Standards	Accounting Standards Recently Adopted We did not adopt any ASUs during 2021 that are expected to have a material impact to our financial statements or financial statement disclosures. Not Yet 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. Guidance must be applied to our annual financial statements for year ended 2022 either prospectively for any transactions reflected in the financial statement at the date of initial application and to any new transactions entered into after the date of initial application or retrospectively to those transactions. Early application is permitted. While we are still evaluating the impact of ASU 2021-10, we do not expect to the adoption of this standard to have a material impact on our consolidated financial statements.

Acquisitions

Acquisitions	12 Months Ended
	Dec. 31, 2021
Business Combinations [Abstract]
Business Combination Disclosure [Text Block]	Acquisitions and Dispositions Sale of Javelina On February 12, 2021, MarkWest Energy Operating Company, L.L.C., (“MarkWest Energy”) a wholly owned subsidiary of MPLX, completed the sale of all of MarkWest Energy’s equity interests in MarkWest Javelina Company L.L.C., MarkWest Javelina Pipeline Company L.L.C., and MarkWest Gas Services L.L.C. (collectively, “Javelina”) pursuant to the terms of an Equity Purchase Agreement entered into with a third party on December 23, 2020. The agreement included adjustments for working capital as well as an earnout provision based on the performance of the assets. No gain or loss was recorded on the sale. The estimated value of the earnout provision was recorded as a contingent asset shown within “Other noncurrent assets” on the Consolidated Balance Sheets as of December 31, 2021. Javelina’s assets and liabilities sold are shown on the Consolidated Balance Sheet as “Assets held for sale” and “Liabilities held for sale”, respectively, for the year ended December 31, 2020. Prior to the sale, Javelina was reported within the G&P segment. Wholesale Exchange On July 31, 2020, MPLX entered into a Redemption Agreement (the “Redemption Agreement”) with WRSW, a wholly owned subsidiary of MPC, pursuant to which MPLX agreed to transfer to WRSW all of the outstanding membership interests in WRW in exchange for the redemption of MPLX common units held by WRSW. The transaction effects the transfer to MPC of the Western wholesale distribution business that MPLX acquired as a result of its acquisition of ANDX as described below. Per the terms of the Redemption Agreement, MPLX redeemed 18,582,088 common units (the “Redeemed Units”) held by WRSW on July 31, 2020. The number of Redeemed Units was calculated by dividing WRW’s aggregate valuation of $340 million by the simple average of the volume weighted average NYSE prices of an MPLX common unit for the ten trading days ending at market close on July 27, 2020. MPLX canceled the Redeemed Units immediately following the Wholesale Exchange. The carrying value of the net assets of WRW transferred to MPC was approximately $90 million as of July 31, 2020, resulting in $250 million being recorded to “Common Unit-holder MPC” within the Consolidated Statements of Equity, netted against the fair value of the redeemed units. Included within the $90 million carrying value of the WRW net assets was approximately $65 million of goodwill. Acquisition of Andeavor Logistics LP On May 7, 2019, ANDX, Tesoro Logistics GP, LLC, then the general partner of ANDX, MPLX, MPLX GP LLC, the general partner of MPLX (“MPLX GP”), and MPLX MAX LLC, a wholly owned subsidiary of MPLX (“Merger Sub”), entered into an Agreement and Plan of Merger (the “Merger Agreement”) that provided for, among other things, the merger of Merger Sub with and into ANDX. On July 30, 2019, the Merger was completed, and ANDX survived the Merger as a wholly owned subsidiary of MPLX. At the effective time of the Merger, each common unit held by ANDX’s public unitholders was converted into the right to receive 1.135 MPLX common units. ANDX common units held by certain affiliates of MPC were converted into the right to receive 1.0328 MPLX common units. See Note 7 for information on common units issued in connection with the Merger as well as Series B preferred units. As a result of the Merger, the ANDX Special Limited Partner Interest outstanding immediately prior to the effective time of the Merger was converted into a right for WRSW, as the holder of all such interest, to receive a substantially equivalent special limited partner interest in MPLX (the “MPLX Special Limited Partner Interest”). By virtue of the conversion, the ANDX Special Limited Partner Interest was cancelled and ceased to exist as of the effective time of the Merger. For information on ANDX’s preferred units, please see Note 7. The assets of ANDX consist of a network of owned and operated crude oil, refined product and natural gas pipelines; crude oil and water gathering systems; refining logistics assets; terminals with crude oil and refined products storage capacity; rail facilities; marine terminals including storage; bulk petroleum distribution facilities; a trucking fleet; and natural gas processing and fractionation complexes. The assets are located in the western and inland regions of the United States and complement MPLX’s existing business and assets. MPC accounted for its October 1, 2018 acquisition of Andeavor (through which it acquired control of ANDX) using the acquisition method of accounting, which required Andeavor assets and liabilities to be recorded by MPC at the acquisition date fair value. The Merger was closed on July 30, 2019, and the results of ANDX have been incorporated into the results of MPLX as of October 1, 2018, which is the date that common control was established. As a result of MPC’s relationship with both MPLX and ANDX, the Merger has been treated as a common control transaction, which requires the recasting of MPLX’s historical results and the recognition of assets acquired and liabilities assumed using MPC’s historical carrying value. Acquisition Costs We recognized $14 million in acquisition costs during 2019, which are reflected in general and administrative expenses. ANDX Revenue and Net Income For the year ended December 31, 2019, we recognized $2.4 billion of revenues and other income related to ANDX and $266 million of net loss related to ANDX, which was impacted by the goodwill impairment discussed in Note 14. Pro Forma Financial Information Pro forma net income attributable to MPLX for the year ended December 31, 2019, including the historical operations of ANDX, giving effect to the merger as if it had been in effect for the full year 2019 was $1,434 million.

Investments and Noncontrolling

Investments and Noncontrolling Interests	12 Months Ended
	Dec. 31, 2020
Equity Method Investments and Joint Ventures [Abstract]
Investments and Noncontrolling Interests	Investments and Noncontrolling Interests The following table presents MPLX’s equity method investments at the dates indicated: Ownership as of Carrying value at December 31, December 31, (In millions, except ownership percentages) 2021 2021 2020 L&S MarEn Bakken Company LLC (1) 25% $ 449 $ 465 Illinois Extension Pipeline Company, L.L.C. 35% 243 254 LOOP LLC 41% 265 252 Andeavor Logistics Rio Pipeline LLC (2) 67% 183 194 Minnesota Pipe Line Company, LLC 17% 183 188 Whistler Pipeline LLC (2) 38% 155 185 W2W Holdings LLC (2) 50% 58 72 Explorer Pipeline Company 25% 66 72 Other (2) 116 103 Total L&S 1,718 1,785 G&P MarkWest Utica EMG, L.L.C. (2) 57% 680 698 Sherwood Midstream LLC (2) 50% 544 557 MarkWest EMG Jefferson Dry Gas Gathering Company, L.L.C. (2) 67% 332 307 MarkWest Torñado GP, L.L.C. (2) 60% 246 188 Rendezvous Gas Services, L.L.C. (2) 78% 147 159 Sherwood Midstream Holdings LLC (2) 51% 136 148 Centrahoma Processing LLC 40% 133 145 Other (2) 45 49 Total G&P 2,263 2,251 Total $ 3,981 $ 4,036 (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 and 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 December 31, 2021, MPLX had 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 years ended December 31, 2021, 2020 and 2019. During the first quarter of 2020, we recorded an other than temporary impairment for three joint ventures in which we have an interest. Impairment of these investments was $1,264 million, of which $1,251 million was related to MarkWest Utica EMG, L.L.C. and its investment in Ohio Gathering Company, L.L.C. The fair value of the investments was determined based upon applying the discounted cash flow method, which is an income approach. The discounted cash flow fair value estimate is based on known or knowable information at the interim measurement date. The significant assumptions that were used to develop the estimate of the fair value under the discounted cash flow method include management’s best estimates of the expected future cash flows, including prices and volumes, the weighted average cost of capital and the long-term growth rate. Fair value determinations require considerable judgment and are sensitive to changes in underlying assumptions and factors. As such, the fair value of these equity method investments represents a Level 3 measurement. As a result, there can be no assurance that the estimates and assumptions made for purposes of the impairment test will prove to be an accurate prediction of the future. The impairment was recorded through “Income from equity method investments.” The impairments were largely due to a reduction in forecasted volumes gathered and processed by the systems operated by the joint ventures. There were no additional impairments recorded during the remainder of 2020. During the fourth quarter of 2019, two joint ventures in which we have an interest recorded impairments, which impacted the amount of income from equity method investments during the period by approximately $28 million and took the carrying value of one of the investments to zero. For the other joint venture, we had a basis difference recorded which was being amortized over the life of the underlying assets. As a result of the impairment recorded by the joint venture, we assessed our investment, including the related basis difference, for impairment and recorded an additional $14 million of impairment during the quarter related to our basis difference. The fair value of the investment was determined based upon applying the discounted cash flow method, which is an income approach. The discounted cash flow fair value estimate is based on known or knowable information at the interim measurement date. The significant assumptions that were used to develop the estimate of the fair value under the discounted cash flow method include management’s best estimates of the expected future results using a probability-weighted average set of cash flow forecasts and the discount rate. The impairment of the basis difference was also recorded through “Income from equity method investments” for a total impact during the quarter of approximately $42 million. The impairments were largely due to a reduction in forecasted volumes of the joint ventures. Summarized financial information for MPLX’s equity method investments for the years ended December 31, 2021, 2020 and 2019 is as follows: December 31, 2021 (In millions) Other VIEs Non-VIEs Total Revenues and other income $ 820 $ 1,236 $ 2,056 Costs and expenses 490 568 1,058 Income from operations 330 668 998 Net income 266 594 860 Income from equity method investments (1) $ 175 $ 146 $ 321 December 31, 2020 (In millions) Other VIEs Non-VIEs Total Revenues and other income $ 298 $ 1,208 $ 1,506 Costs and expenses 414 531 945 (Loss)/income from operations (116) 677 561 Net (loss)/income (175) 615 440 (Loss)/income from equity method investments (1) $ (1,100) $ 164 $ (936) December 31, 2019 (2) (In millions) Other VIEs Non-VIEs Total Revenues and other income $ 650 $ 1,417 $ 2,067 Costs and expenses 375 568 943 Income from operations 275 849 1,124 Net income 215 752 967 Income from equity method investments (1) $ 103 $ 187 $ 290 (1) The 2021, 2020 and 2019 amounts include impairment of $6 million, $1,264 million and $42 million, respectively. (2) The financial information for equity method investments for 2019 includes financial information of equity method investments acquired as part of the Merger. Summarized balance sheet information for MPLX’s equity method investments as of December 31, 2021 and 2020 is as follows: December 31, 2021 (In millions) Other 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 December 31, 2020 (In millions) Other VIEs Non-VIEs Total Current assets $ 530 $ 318 $ 848 Noncurrent assets 6,889 4,997 11,886 Current liabilities 323 187 510 Noncurrent liabilities $ 1,904 $ 830 $ 2,734 As of December 31, 2021 and 2020, the underlying net assets of MPLX’s investees in the G&P segment exceeded the carrying value of its equity method investments by approximately $54 million and $57 million, respectively. As of December 31, 2021 and 2020, the carrying value of MPLX’s equity method investments in the L&S segment exceeded the underlying net assets of its investees by $327 million and $331 million, respectively. At both December 31, 2021 and 2020, the G&P basis difference related to goodwill was $31 million. At both December 31, 2021 and 2020, the L&S basis difference related to goodwill was $167 million.

Related Party Agreements and Tr

Related Party Agreements and Transactions	12 Months Ended
	Dec. 31, 2021
Related Party Transactions [Abstract]
Related Party Transactions Disclosure [Text Block]	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 and 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. In addition, MPLX has obligations to MPC for services provided to MPLX by MPC under omnibus and employee services type agreements as well as other various agreements as discussed below. The commercial agreements with MPC include: • MPLX has a fuels distribution agreement with MPC under which MPC pays MPLX a tiered monthly volume-based fee for marketing and selling MPC’s products. This agreement is subject to a minimum quarterly volume and has an initial term of 10 years, subject to a five • MPLX has various pipeline transportation agreements under which MPC pays MPLX fees for transporting crude and refined products on MPLX’s pipeline systems. These agreements are subject to minimum throughput volumes under which MPC will pay MPLX deficiency payments for any period in which they do not ship the minimum committed volume. These deficiency payments can be applied as credits to future periods in which MPC ships volumes in excess of the minimum volume, subject to a limited period of time. These agreements are subject to various terms and renewal periods. • MPLX has a marine transportation agreement with an initial term of six years under which MPC pays MPLX fees for providing marine transportation of crude oil, feedstock and refined petroleum products, and related services. This agreement is subject to two automatic renewal periods of five years each. This agreement is currently in the first renewal term. • MPLX has a month-to-month trucking transportation services agreement under which MPC pays MPLX fees for gathering barrels and providing trucking, dispatch, delivery and data services. • MPLX has numerous storage services agreements governing storage services at various types of facilities including terminals, pipeline tank farms, caverns and refineries, under which MPC pays MPLX per-barrel fees for providing storage services. Some of these agreements provide MPC with exclusive access to storage at certain locations, such as storage located at MPC’s refineries or storage in certain caverns. Under these agreements, MPC pays MPLX a per-barrel fee for such storage capacity, regardless of whether MPC fully utilizes the available capacity. Many of the refinery storage agreements also contain provisions for logistical services to be provided by MPLX, for which MPC pays monthly fees. These agreements are subject to various terms and renewal periods. • MPLX has multiple terminal services agreements governing certain terminals under which MPC pays MPLX fees for terminal services for refined petroleum products. Under these agreements MPC pays MPLX agreed upon fees relating to MPC product receipts, deliveries and storage as well as any blending, additization, handling, transfers or other related charges. Many of these agreements are subject to minimum volume throughput commitments, or to various minimum commitments related to some or all terminal activities, under which MPC pays a deficiency payment for any period in which they do not meet the minimum commitment. Some of these agreements allow for deficiency payments to be applied as credits to a limited number of future periods with excess throughput volumes. These agreements are subject to various terms and renewal periods. • MPLX has a year to year 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. The pricing structure under this agreement provides for a base volume subject to a base rate and incremental volumes subject to variable rates which are calculated with reference to certain of our costs incurred as processor of the volumes. The pricing for both the base and incremental volumes are subject to revision each year. In many cases, agreements are location-based hybrid agreements, containing provisions relating to multiple of the types of agreements and services described above. Operating Agreements MPLX operates various pipelines owned by MPC under operating services agreements. Under these operating services agreements, MPLX receives an operating fee for operating the assets and is reimbursed for all direct and indirect costs associated with operating the assets. Most of these agreements are indexed for inflation. These agreements range from one Co-location Services Agreements MPLX is party to co-location services agreements with MPC’s refineries, under which MPC provides management, operational and other services to the subsidiaries of MPLX Refining Logistics LLC (“Refining Logistics”). Refining Logistics pays MPC monthly fixed fees and direct reimbursements for such services calculated as set forth in the agreements. These agreements have initial terms of 50 years. Ground Lease Agreements MPLX is party to ground lease agreements with certain of MPC’s refineries under which MPLX is the lessor of certain sections of property which contain facilities owned by Refining Logistics and are within the premises of MPC’s refineries. Refining Logistics pays MPC monthly fixed fees under these ground leases. These agreements are subject to various terms. Marine Services Agreements with MPC MPLX has a management services agreement and a loss control agreement with MPC under which it provides management and loss control services to assist MPC in the oversight and management of the marine business. MPLX receives fixed annual fees for providing the required services, which are subject to predetermined annual escalation rates. These agreements are subject to initial terms of five years and automatically renew for one additional five Omnibus Agreements MPLX has omnibus agreements with MPC that address MPLX’s payment of fixed annual fees to MPC for the provision of executive management services by certain executive officers of the general partner and MPLX’s reimbursement of MPC for the provision of certain general and administrative services to it. They also provide for MPC’s indemnification to MPLX for certain matters, including environmental, title and tax matters; as well as our indemnification of MPC for certain matters under these agreements. Employee Services Agreements MPLX has various employee services agreements and secondment agreements with MPC under which MPLX reimburses MPC for employee benefit expenses, along with the provision of operational and management services in support of both our L&S and G&P segments’ operations. Loan Agreement MPLX is party to a loan agreement (the “MPC Loan Agreement”) with MPC Investment LLC (“MPC Investment”), a wholly owned subsidiary of MPC. Under the terms of the MPC Loan Agreement, MPC Investment extends loans to MPLX on a revolving basis as requested by MPLX and as agreed to by MPC Investment. The MPC Loan Agreement has a borrowing capacity of $1.5 billion in aggregate principal amount of all loans outstanding at any one time. The MPC Loan Agreement is scheduled to expire, and borrowings under the MPC 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 the maturity date. Borrowings under the MPC Loan Agreement prior to July 31, 2019 bore interest at LIBOR plus 1.50 percent, while borrowings as of and after July 31, 2019 will bear interest at the one-month 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 17. Activity on the MPC Loan Agreement was as follows: (In millions, except %) December 31, 2021 December 31, 2020 Borrowings $ 8,493 $ 6,264 Average interest rate of borrowings 1.341 % 2.278 % Repayments $ 7,043 $ 6,858 Outstanding balance at end of period $ 1,450 $ — Related Party Revenue Related party sales to MPC consist of crude oil and refined products pipeline and trucking transportation services based on tariff/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. There were additional product sales to MPC that 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 years ended December 31, 2021, 2020 and 2019, these sales totaled $811 million, $462 million and $1,120 million, respectively . Related Party Expenses MPC provides executive management services and certain general and administrative services to MPLX under the terms of our omnibus agreements. 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 rent and lease agreements with MPC. MPC has also been advancing certain strategic priorities to lay a foundation for long-term success, including plans to optimize its assets and structurally lower costs in 2021 and beyond, which included an involuntary workforce reduction plan. The workforce reduction plan, together with employee reductions resulting from MPC's indefinite idling of its Martinez, California and Gallup, New Mexico refineries, affected approximately 2,050 employees. All of the employees that conduct MPLX’s business are directly employed by affiliates of MPC, and certain of those employees were affected by MPC’s workforce reductions. During 2020, MPLX reimbursed MPC for $37 million related to severance and employee benefits related expenses that MPC recorded in connection with its workforce reductions. These costs are shown on the Consolidated Statements of Income as “Restructuring expenses.” There were no similar costs in 2021. For the years ended December 31, 2021, 2020 and 2019, “General and administrative expenses” incurred from MPC totaled $250 million, $254 million and $243 million, respectively. Some charges incurred under the omnibus and employee service 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 2021, 2020 and 2019, these charges totaled $55 million, $97 million and $169 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 (see Note 20 for additional information) 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. December 31, (In millions) 2021 2020 Current assets - related parties Receivables - MPC $ 548 $ 615 Receivables - Other 7 27 Prepaid - MPC 4 4 Other - MPC 3 1 Lease Receivables - MPC 82 30 Total 644 677 Noncurrent assets - related parties Long-term receivables - MPC 31 32 Right of use assets - MPC 229 231 Long-term lease receivables - MPC 854 386 Unguaranteed residual asset - MPC 47 23 Total 1,161 672 Current liabilities - related parties Payables - MPC (1) 1,657 215 Payables - Other 45 43 Operating lease liabilities - MPC 1 1 Deferred revenue - Minimum volume deficiencies - MPC 35 66 Deferred revenue - Project reimbursements - MPC 41 30 Deferred revenue - Project reimbursements - Other 1 1 Total 1,780 356 Long-term liabilities - related parties Long-term operating lease liabilities - MPC 228 229 Long-term deferred revenue - Project reimbursements - MPC 68 47 Long-term deferred revenue - Project reimbursements - Other 6 7 Total $ 302 $ 283 (1) Includes $1,450 million as of the year ended December 31, 2021 related to outstanding borrowings on the intercompany loan with MPC.

Equity

Equity	12 Months Ended
	Dec. 31, 2021
Equity [Abstract]
Equity	Equity Units Outstanding MPLX had 1,016,178,378 common units outstanding as of December 31, 2021. Of that number, 647,415,452 were owned by MPC, which also owns the non-economic GP Interest as described below. MPLX had 600,000 Series B preferred units outstanding as of December 31, 2021. The sections below describe activities and events which impacted our unit balances throughout the three years ended December 31, 2021. 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. The table below summarizes the repurchases made under the unit repurchase program for the years ended December 31, 2021 and 2020: 2021 2020 Number of units repurchased 22,907,174 1,473,843 Cash paid for units repurchased (in millions) $ 630 $ 33 Average cost per unit $ 27.52 $ 22.29 As of December 31, 2021 we had $337 million remaining available under the program for future repurchases. Wholesale Exchange and Merger In connection with the Wholesale Exchange as discussed in Note 4, MPLX redeemed 18,582,088 units from MPC in exchange for all of the outstanding membership interests in WRW. These units were cancelled by MPLX immediately following the transaction. In connection with the Merger and as discussed in Note 4, each common unit held by ANDX’s public unitholders was converted into the right to receive 1.135 MPLX common units while ANDX common units held by certain affiliates of MPC were converted into the right to receive 1.0328 MPLX common units. This resulted in the issuance of MPLX common units of approximately 102 million units to public unitholders and approximately 161 million units to MPC in connection with MPLX's acquisition of ANDX on July 30, 2019. Series A Redeemable Preferred Unit Conversions - Since 2019, certain Series A preferred unitholders have exercised their rights to convert their Series A preferred units into approximately 1.2 million common units as discussed in Note 9. The table below summarizes the changes in the number of units outstanding for the years ended December 31, 2019, 2020, and 2021: (In units) Total Common Units Balance at December 31, 2018 794,089,518 Unit-based compensation awards 288,031 Issuance of units in connection with the Merger (See Note 4) 262,829,592 Conversion of Series A preferred units 1,148,330 Balance at December 31, 2019 1,058,355,471 Unit-based compensation awards 478,438 Wholesale Exchange (18,582,088) Units redeemed in unit repurchase program (1,473,843) Balance at December 31, 2020 1,038,777,978 Unit-based compensation awards 214,466 Conversion of Series A preferred units 93,108 Units redeemed in unit repurchase program (22,907,174) Balance at December 31, 2021 1,016,178,378 Series B Preferred Units - Prior to the Merger, ANDX issued 600,000 units of 6.875 percent Fixed-to-Floating Rate Cumulative Redeemable Perpetual Preferred Units representing limited partner interests of ANDX at a price to the public of $1,000 per unit. Upon completion of the Merger, the ANDX preferred units converted to preferred units of MPLX representing substantially equivalent limited partnership interests in MPLX. The Series B preferred units are pari passu with the Series A preferred units with respect to distribution rights and rights upon liquidation. MPLX has the right to redeem some or all of the Series B preferred units, at any time, on or after February 15, 2023. MPLX will pay unitholders the Series B preferred unit redemption price of $1,000 per unit plus any accumulated and unpaid distributions up to the redemption date. Distributions on the Series B preferred units are 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. The changes in the Series B preferred unit balance for 2021 and 2020 are included in the Consolidated Balance Sheets and Consolidated Statements of Equity within “Equity of Predecessor” for the period prior to the Merger and within “Series B preferred units” for the period following the Merger. The Series B preferred units were recorded at fair value as of July 30, 2019. Issuance of Additional Securities – The Sixth Amended and Restated Agreement of Limited Partnership of MPLX LP, dated as of February 1, 2021 (“Partnership Agreement”), authorizes MPLX to issue an unlimited number of additional securities for the consideration and on the terms and conditions determined by the general partner without the approval of the unitholders. Net Income Allocation – In preparing the Consolidated Statements of Equity, net income attributable to MPLX LP is allocated to Series A and Series B preferred unitholders first and subsequently allocated to the limited partner unitholders in accordance with their respective ownership percentages. Cash Distributions – The Partnership Agreement sets forth the calculation to be used to determine the amount and priority of cash distributions that the common unitholders and preferred unitholders will receive. On January 25, 2022, MPLX declared a quarterly cash distribution, based on the results of the fourth quarter of 2021, totaling $715 million, or $0.7050 per common unit. This rate was also received by Series A preferred unitholders. These distributions were paid on February 14, 2022 to unitholders of record on February 4, 2022. Total distributions for the twelve months ended December 31, 2021, 2020 and 2019 are summarized in the table below. The 2021 period includes a special distribution amount of $0.575 per common unit (the “Special Distribution Amount”) related to the distribution declared for the third quarter of 2021, which was paid during the fourth quarter of 2021. 2021 2020 2019 Distributions per common unit $ 3.36 $ 2.75 $ 2.69 Additionally, in accordance with the distribution rights discussed above, MPLX made a cash distribution to holders of the Series B preferred unitholders on February 15, 2022 of approximately $21 million. The allocation of total quarterly cash distributions to general, limited, and preferred unitholders is as follows for the years ended December 31, 2021, 2020 and 2019. 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. (In millions) 2021 2020 2019 Limited partners' distributions: Common unitholders, includes common units of general partner (1) $ 3,432 $ 2,872 $ 2,635 Series A preferred unit distributions (1) 100 81 81 Series B preferred unit distribution 41 41 42 Total cash distributions declared $ 3,573 $ 2,994 $ 2,758 (1) 2021 period includes the Special Distribution Amount.

Net Income (Loss) Per Limited P

Net Income (Loss) Per Limited Partner Unit	12 Months Ended
	Dec. 31, 2021
Earnings Per Share [Abstract]
Earnings Per Share [Text Block]	Net Income/(Loss) Per Limited Partner Unit Net income/(loss) per unit applicable to common limited partner units is computed by dividing net income/(loss) attributable to MPLX LP less income/(loss) allocated to participating securities by the weighted average number of common units outstanding. Classes of participating securities include common units, equity-based compensation awards, Series A preferred units and Series B preferred units. Additional MPLX common units and MPLX Series B preferred units were issued on July 30, 2019 as a result of the Merger as discussed in Note 4. Distributions declared on these newly issued common and Series B preferred units are a reduction to income available to MPLX common unit holders due to their participation in distributions of income. The Merger was a transfer between entities under common control as discussed in Note 4. As entities under common control with MPC, prior periods were retrospectively adjusted to furnish comparative information. Accordingly, the prior period earnings have been allocated to the general partner and do not affect the net income/(loss) per unit calculation. The earnings for the entities acquired under common control will be included in the net income/(loss) per unit calculation prospectively as described above. In 2021, 2020 and 2019, MPLX had dilutive potential common units consisting of certain equity-based compensation awards. Anti-dilutive potential common units omitted from the diluted earnings per unit calculation for the years ended December 31, 2021, 2020 and 2019 were less than 1 million. (In millions) 2021 2020 2019 Net income/(loss) attributable to MPLX LP $ 3,077 $ (720) $ 1,033 Less: Distributions declared on Series A preferred units (1) 100 81 81 Distributions declared on Series B preferred units 41 41 42 Limited partners’ distributions declared on MPLX common units (including common units of general partner) (1)(2) 3,432 2,872 2,635 Undistributed net loss attributable to MPLX LP $ (496) $ (3,714) $ (1,725) (1) The year ended December 31, 2021 includes the Special Distribution Amount. (2) Distributions on common units exclude $37.5 million of waived distributions for the year ended December 31, 2019, with respect to units held by MPC and its affiliates. 2021 (In millions, except per unit data) Limited 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 $ 3,432 $ 100 $ 41 $ 3,573 Undistributed net loss attributable to MPLX LP (496) — — (496) Net income attributable to MPLX LP $ 2,936 $ 100 $ 41 $ 3,077 Weighted average units outstanding: Basic 1,027 1,027 Diluted 1,027 1,027 Net income attributable to MPLX LP per limited partner unit: Basic $ 2.86 Diluted $ 2.86 2020 (In millions, except per unit data) Limited Series A Preferred Units Series B Preferred Units Total Basic and diluted net (loss)/income attributable to MPLX LP per unit: Net (loss)/income attributable to MPLX LP: Distributions declared $ 2,872 $ 81 $ 41 $ 2,994 Undistributed net loss attributable to MPLX LP (3,714) — — (3,714) Net (loss)/income attributable to MPLX LP $ (842) $ 81 $ 41 $ (720) Weighted average units outstanding: Basic 1,051 1,051 Diluted 1,051 1,051 Net loss attributable to MPLX LP per limited partner unit: Basic $ (0.80) Diluted $ (0.80) 2019 (In millions, except per unit data) Limited 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: Distribution declared $ 2,635 $ 81 $ 42 $ 2,758 Undistributed net loss attributable to MPLX LP (1,725) — — (1,725) Net income attributable to MPLX LP $ 910 $ 81 $ 42 $ 1,033 Weighted average units outstanding: Basic 906 906 Diluted 907 907 Net income attributable to MPLX LP per limited partner unit: Basic $ 1.00 Diluted $ 1.00

Redeemable Preferred Units

Redeemable Preferred Units	12 Months Ended
	Dec. 31, 2021
Redeemable Preferred Units Disclosure [Abstract]
Redeemable Preferred Units	Series A Preferred Units Private Placement of Preferred Units – On May 13, 2016, MPLX completed the private placement of approximately 30.8 million 6.5 percent Series A Convertible preferred units for a cash purchase price of $32.50 per unit. The aggregate net proceeds of approximately $984 million from the sale of the Series A preferred units were used for capital expenditures, repayment of debt and general business purposes. Preferred Unit Distribution Rights - The Series A preferred units rank senior to all common units and pari passu with all Series B preferred units with respect to distributions and rights upon liquidation. The holders of the Series A preferred units are entitled to receive, when and if declared by the board, a quarterly distribution equal to the greater of $0.528125 per unit or the amount of distributions they would have received on an as converted basis, including any special distributions made to common unitholders. On January 25, 2022, MPLX declared a quarterly cash distribution of $0.7050 per common unit for the fourth quarter of 2021. Holders of the Series A preferred units received the common unit rate in lieu of the lower $0.528125 base amount. The holders may convert their Series A preferred units into common units at any time, in full or in part, subject to minimum conversion amounts and conditions. After the fourth anniversary of the issuance date, MPLX may convert the Series A preferred units into common units at any time, in whole or in part, subject to certain minimum conversion amounts and conditions, if the closing price of MPLX common units is greater than $48.75 for the 20-day trading period immediately preceding the conversion notice date. The conversion rate for the Series A preferred units shall be the quotient of (a) the sum of (i) $32.50, plus (ii) any unpaid cash distributions on the applicable preferred unit, divided by (b) $32.50, subject to adjustment for unit distributions, unit splits and similar transactions. The holders of the Series A preferred units are entitled to vote on an as-converted basis with the common unitholders and have certain other class voting rights with respect to any amendment to the MPLX partnership agreement that would adversely affect any rights, preferences or privileges of the preferred units. In addition, upon certain events involving a change of control, the holders of preferred units may elect, among other potential elections, to convert their Series A preferred units to common units at the then applicable change of control conversion rate. Preferred Units Outstanding - During 2019 and 2021, certain holders exercised their right to convert a total of 1.15 million and 0.1 million Series A preferred units into common units, respectively. As a result of these transactions, approximately 29.5 million Series A preferred units remain outstanding as of December 31, 2021. For detailed information regarding the conversion of Series A preferred units to common units see Note 7. Financial Statement Presentation - The Series A preferred units are considered redeemable securities under GAAP due to the existence of redemption provisions upon a deemed liquidation event, which is outside MPLX’s control. Therefore, they are presented as temporary equity in the mezzanine section of the Consolidated Balance Sheets. The Series A preferred units have been recorded at their issuance date fair value, net of issuance costs. Income allocations increase the carrying value and declared distributions decrease the carrying value of the Series A preferred units. As the Series A preferred units are not currently redeemable and not probable of becoming redeemable, adjustment to the initial carrying amount is not necessary and would only be required if it becomes probable that the Series A preferred units would become redeemable. For a summary of changes in the redeemable preferred balance for 2021, 2020 and 2019, see the Consolidated Statements of Equity.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2021
Segment Reporting [Abstract]
Segment Information	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) provision/(benefit) for income taxes; (iii) amortization of deferred financing costs; (iv) gain/(loss) on extinguishment of debt; (v) non-cash equity-based compensation; (vi) impairment expense; (vii) net interest and other financial costs; (viii) income/(loss) from equity method investments; (ix) distributions and adjustments related to equity method investments; (x) unrealized derivative gains/(losses); (xi) acquisition costs; (xii) noncontrolling interests; and (xiii) 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 as well as total assets for our reportable segments: (In millions) 2021 2020 2019 L&S Service revenue $ 3,918 $ 3,889 $ 3,765 Rental income 772 985 1,235 Sales-type lease revenue 435 152 7 Product related revenue 14 51 91 Income from equity method investments 153 154 200 Other income 61 54 54 Total segment revenues and other income (1) 5,353 5,285 5,352 Segment Adjusted EBITDA (2) 3,681 3,488 2,748 Restructuring expenses — 29 — Capital expenditures (3) 316 498 1,060 Investments in unconsolidated affiliates 33 141 289 G&P Service revenue 2,023 2,088 2,188 Rental income 347 365 349 Product related revenue 2,066 868 997 Income/(loss) from equity method investments 168 (1,090) 90 Other income 70 53 65 Total segment revenues and other income (1) 4,674 2,284 3,689 Segment Adjusted EBITDA (2) 1,879 1,723 1,586 Restructuring expenses — 8 — Capital expenditures (3) 224 441 1,203 Investments in unconsolidated affiliates $ 118 $ 125 $ 424 (1) Within the total segment revenues and other income amounts presented above, third party revenues for the L&S segment were $503 million, $567 million and $660 million for 2021, 2020 and 2019, respectively. Third party revenues for the G&P segment were $4,463 million, $2,088 million and $3,474 million for 2021, 2020 and 2019, respectively. (2) See below for the reconciliation from Segment Adjusted EBITDA to “Net income/(loss).” (3) Capital expenditures do not include adjustments for asset retirement expenditures. December 31, (In millions) 2021 2020 Segment assets Cash and cash equivalents $ 13 $ 15 L&S 20,655 20,938 G&P 14,839 15,461 Total assets $ 35,507 $ 36,414 The table below provides a reconciliation between “Net income” and Segment Adjusted EBITDA. (In millions) 2021 2020 2019 Reconciliation to Net income/(loss): L&S Segment Adjusted EBITDA $ 3,681 $ 3,488 $ 2,748 G&P Segment Adjusted EBITDA 1,879 1,723 1,586 Total reportable segments 5,560 5,211 4,334 Depreciation and amortization (1) (1,287) (1,377) (1,254) Provision for income taxes (1) (2) — Amortization of deferred financing costs (70) (61) (42) Gain on extinguishment of debt 10 19 — Non-cash equity-based compensation (9) (14) (22) Impairment expense (42) (2,165) (1,197) Net interest and other financial costs (819) (854) (873) Income/(loss) from equity method investments 321 (936) 290 Distributions/adjustments related to equity method investments (537) (499) (562) Unrealized derivative (losses)/gains (2) (45) (3) 1 Acquisition costs — — (14) Restructuring expenses — (37) — Other (8) (6) (1) Adjusted EBITDA attributable to noncontrolling interests 39 37 32 Adjusted EBITDA attributable to Predecessor (3) — — 770 Net income/(loss) $ 3,112 $ (687) $ 1,462 (1) Depreciation and amortization attributable to L&S was $546 million, $633 million and $503 million for the years ended 2021, 2020 and 2019, respectively. Depreciation and amortization attributable to G&P was $741 million, $744 million and $751 million for 2021, 2020 and 2019, respectively. (2) MPLX makes 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. (3) The Adjusted EBITDA adjustments related to Predecessor are excluded from Adjusted EBITDA attributable to MPLX LP prior to the acquisition date.

Major Customers and Concentrati

Major Customers and Concentration of Credit Risk	12 Months Ended
	Dec. 31, 2021
Risks and Uncertainties [Abstract]
Major Customers and Concentration of Credit Risk	Major Customers and Concentration of Credit Risk The table below shows, by segment, the percentage of operating revenues as well as total revenues and other income with MPC which is our most significant customer and our largest concentration of credit risk. 2021 2020 2019 Total revenues and other income (1) L&S 90 % 89 % 88 % G&P 3 % 4 % 4 % Total 50 % 55 % 53 % (1) The percent calculations exclude losses attributable to the impairment of equity method investments. MPLX has a concentration of trade receivables due from customers in the same industry: MPC, integrated oil companies, natural gas exploration and production companies, independent refining companies and other pipeline companies. These concentrations of customers may impact MPLX’s overall exposure to credit risk as they may be similarly affected by changes in economic, regulatory and other factors. MPLX manages its exposure to credit risk through credit analysis, credit limit approvals and monitoring procedures; and for certain transactions, it may request letters of credit, prepayments or guarantees.

Inventories

Inventories	12 Months Ended
	Dec. 31, 2021
Inventory Disclosure [Abstract]
Inventories	Inventories Inventories consist of the following: December 31, (In millions) 2021 2020 NGLs $ 12 $ 5 Line fill 23 13 Spare parts, materials and supplies 107 100 Total inventories $ 142 $ 118

Property, Plant and Equipment

Property, Plant and Equipment	12 Months Ended
	Dec. 31, 2021
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property, Plant and Equipment Property, plant and equipment with associated accumulated depreciation is shown below: Estimated December 31, (In millions) 2021 2020 L&S Pipelines 3-50 years $ 6,299 $ 6,026 Refining logistics 13-40 years 1,650 2,333 Terminals 4-40 years 1,655 1,643 Marine 15-20 years 965 965 Land, building and other 2-60 years 1,589 1,584 Construction-in-progress 213 262 Total L&S property, plant and equipment 12,371 12,813 G&P Gathering and transportation 5-40 years 7,668 7,547 Processing and fractionation 10-40 years 5,795 5,721 Land, building and other 3-40 years 514 507 Construction-in-progress 198 287 Total G&P property, plant and equipment 14,175 14,062 Total property, plant and equipment 26,546 26,875 Less accumulated depreciation (1) 6,504 5,657 Property, plant and equipment, net $ 20,042 $ 21,218 (1) Includes property, plant and equipment impairment charges recorded during the respective period, as discussed below. Long-lived assets used in operations are assessed for impairment whenever changes in facts and circumstances indicate that the carrying value of the assets may not be recoverable based on the expected undiscounted future cash flow of an asset group. For purposes of impairment evaluation, long-lived assets must be grouped at the lowest level for which independent cash flows can be identified, which is at least at the segment level and in some cases for similar assets in the same geographic region where cash flows can be separately identified. If the sum of the undiscounted cash flows is less than the carrying value of an asset group, fair value is calculated, and the carrying value is written down if greater than the calculated fair value. In the second quarter of 2021, we recognized impairment expense of $42 million within our G&P segment related to our continued emphasis on portfolio optimization with the divestiture of several non-core assets and the closure of other non-core assets. During the first quarter of 2020, we identified an impairment trigger relating to asset groups within our Western G&P reporting unit as a result of significant impacts to forecasted cash flows for these asset groups resulting from the deterioration in the economy and the environment in which MPLX and its customers operate, as well as a sustained decrease in unit price. The cash flows associated with these assets were significantly impacted by volume declines reflecting decreased forecasted producer customer production as a result of lower commodity prices. After assessing each asset group within the Western G&P reporting unit for impairment, only the East Texas G&P asset

Goodwill and Intangibles

Goodwill and Intangibles	12 Months Ended
	Dec. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangibles	Goodwill and Intangibles Goodwill MPLX annually evaluates goodwill for impairment as of November 30, as well as whenever events or changes in circumstances indicate it is more likely than not that the fair value of a reporting unit with goodwill is less than its carrying amount. Our reporting units are one level below our operating segments and are determined based on the way in which segment management operates and reviews each operating segment. We have five reporting units, three of which have goodwill allocated to them. For the annual impairment assessment as of November 30, 2021, management performed only a qualitative assessment for one reporting unit as we determined it was more likely than not that the fair value of the reporting unit exceeded the carrying value. The fair value of the two remaining reporting units for which a quantitative assessment was performed was determined based on applying both a discounted cash flow, or income approach, as well as a market approach which resulted in the fair value of the reporting units exceeding their carrying value by 23 percent and 51 percent. The significant assumptions that were used to develop the estimates of the fair values under the discounted cash flow method included management’s best estimates of the discount rate of 7.2 percent as well as estimates of future cash flows, which are impacted primarily by producer customers’ development plans, which impact future volumes and capital requirements. Fair value determinations require considerable judgment and are sensitive to changes in underlying assumptions and factors. As a result, there can be no assurance that the estimates and assumptions made for purposes of the annual goodwill impairment test will prove to be an accurate prediction of the future. The fair value measurements for the individual reporting units represent Level 3 measurements. Total goodwill at December 31, 2021 was $7.7 billion and no impairment was recorded as a result of our November 30, 2021 annual goodwill impairment analysis. During the first quarter of 2020, we determined that an interim impairment analysis of the goodwill recorded was necessary based on consideration of a number of first quarter events and circumstances. Our producer customers in our Eastern G&P region reduced production forecasts and drilling activity in response to the global economic downturn. Additionally, a decline in NGL prices impacted our future revenue forecast. After performing our evaluations related to the interim impairment of goodwill during the first quarter of 2020, we recorded an impairment of $1,814 million within the Eastern G&P reporting unit, which was recorded to “Impairment expense” on the Consolidated Statements of Income. The impairment was primarily driven by additional guidance related to the slowing of drilling activity, which reduced production growth forecasts from our producer customers. The interim impairment assessment of the remaining reporting units with goodwill resulted in the fair value of the reporting units exceeding their carrying value. The fair value of our reporting units was determined based on applying both a discounted cash flow or income approach as well as a market approach. The discounted cash flow fair value estimate is based on known or knowable information at the measurement date. The significant assumptions that were used to develop the estimates of the fair values under the discounted cash flow method included management’s best estimates of the discount rate, which ranged from 9.5 percent to 11.5 percent, as well as estimates of future cash flows, which are impacted primarily by producer customers’ development plans, which impact future volumes and capital requirements. After performing our evaluations related to the impairment of goodwill during the fiscal year ended December 31, 2019, we recorded an impairment of $1,197 million within the Western G&P reporting unit. The fair value of the remaining reporting units’ were in excess of their carrying values. The impairment was primarily driven by updated guidance related to the slowing of drilling activity, which has reduced production growth forecasts from our producer customers. The changes in carrying amount of goodwill were as follows for the periods presented: (In millions) L&S G&P Total Gross goodwill as of December 31, 2019 $ 7,722 $ 3,141 $ 10,863 Accumulated impairment losses — (1,327) (1,327) Balance as of December 31, 2019 7,722 1,814 9,536 Impairment losses — (1,814) (1,814) Wholesale Exchange (Note 4) (65) — (65) Balance as of December 31, 2020 7,657 — 7,657 Impairment losses — — — Balance as of December 31, 2021 7,657 — 7,657 Gross goodwill as of December 31, 2021 7,657 3,141 10,798 Accumulated impairment losses — (3,141) (3,141) Balance as of December 31, 2021 $ 7,657 $ — $ 7,657 Intangible Assets MPLX’s intangible assets are comprised of customer contracts and relationships. Gross intangible assets with accumulated amortization as of December 31, 2021 and 2020 is shown below: December 31, 2021 December 31, 2020 (In millions) Useful Life Gross Accumulated Amortization (1) Net Gross Accumulated Amortization (1)(2) Net L&S 6 - 8 years $ 283 $ (117) $ 166 $ 283 $ (81) $ 202 G&P 6 - 25 years 1,288 (623) 665 1,288 (531) 757 $ 1,571 $ (740) $ 831 $ 1,571 $ (612) $ 959 (1) Amortization expense attributable to the G&P segment for the years ended December 31, 2021 and 2020 was $92 million and $98 million, respectively. Amortization expense attributable to the L&S segment for both years ended December 31, 2021 and 2020 was $36 million. (2) Impairment charge of $177 million is included within the G&P accumulated amortization for the year ended December 31, 2020. During the first quarter of 2020, we also determined that an impairment analysis of intangibles within our Western G&P reporting unit was necessary. See Note 13 for additional information regarding our assessment around the Western G&P reporting unit, and more specifically our East Texas G&P asset group. The fair value of the intangibles in our East Texas G&P asset group were determined based on applying the multi-period excess earnings method, which is an income approach. Key assumptions included management’s best estimates of the expected future cash flows from existing customers, customer attrition rates and the discount rate. After performing our evaluations related to the impairment of intangible assets associated with our East Texas G&P asset group during the first quarter of 2020, we recorded an impairment of $177 million to “Impairment expense” on the Consolidated Statements of Income related to our customer relationships. Estimated future amortization expense related to the intangible assets at December 31, 2021 is as follows: (In millions) 2022 $ 127 2023 127 2024 127 2025 113 2026 104 Thereafter 233 Total $ 831

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2021
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 16. The following table presents the financial instruments carried at fair value on a recurring basis as of December 31, 2021 and 2020 by fair value hierarchy level. MPLX has elected to offset the fair value amounts recognized for multiple derivative contracts executed with the same counterparty. December 31, 2021 2020 (In millions) Assets Liabilities Assets Liabilities Significant unobservable inputs (Level 3) Embedded derivatives in commodity contracts $ — $ (108) $ — $ (63) Total carrying value on Consolidated Balance Sheets $ — $ (108) $ — $ (63) Level 3 instruments include an embedded derivative in commodity contracts. The embedded derivative liability relates to 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 $0.72 to $1.79 per gallon with a weighted average of $0.92 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. 2021 2020 (In millions) Embedded Derivatives in Commodity Contracts (net) Embedded Derivatives in Commodity Contracts (net) Fair value at beginning of period $ (63) $ (60) Total losses (realized and unrealized) included in earnings (1) (59) (9) Settlements 14 6 Fair value at end of period (108) (63) The amount of total losses for the period included in earnings attributable to the change in unrealized gains or losses relating to liabilities still held at end of period $ (47) $ (4) (1) Losses 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 16). 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: December 31, 2021 2020 (In millions) Fair Value Carrying Value Fair Value Carrying Value Outstanding debt (1) $ 20,779 $ 18,664 $ 22,951 $ 20,244 (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	12 Months Ended
	Dec. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments	Derivative Financial Instruments For the years 2021, 2020 and 2019, 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 December 31, 2021 and 2020, 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: December 31, (In millions) 2021 2020 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 $ — $ (15) $ — $ (7) Other noncurrent assets / Deferred credits and other liabilities — (93) — (56) Total $ — $ (108) $ — $ (63) (1) Includes the embedded derivative in the commodity contract discussed above. 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: (In millions) 2021 2020 2019 Purchased product costs Realized loss $ (14) $ (6) $ (6) Unrealized (loss)/gain (45) (3) 1 Purchased product cost derivative loss $ (59) $ (9) $ (5)

Debt

Debt	12 Months Ended
	Dec. 31, 2021
Debt Disclosure [Abstract]
Debt	Debt MPLX’s outstanding borrowings at December 31, 2021 and 2020 consisted of the following: December 31, (In millions) 2021 2020 MPLX LP: Bank revolving credit facility due July 30, 2024 $ 300 $ 175 Floating rate senior notes due September 9, 2022 — 1,000 3.500% senior notes due December 1, 2022 486 486 3.375% senior notes due March 15, 2023 500 500 4.500% senior notes due July 15, 2023 989 989 4.875% senior notes due December 1, 2024 1,149 1,149 5.250% senior notes due January 15, 2025 — 708 4.000% senior notes due February 15, 2025 500 500 4.875% senior notes due June 1, 2025 1,189 1,189 1.750% senior notes due March 1, 2026 1,500 1,500 4.125% senior notes due March 1, 2027 1,250 1,250 4.250% senior notes due December 1, 2027 732 732 4.000% senior notes due March 15, 2028 1,250 1,250 4.800% senior notes due February 15, 2029 750 750 2.650% senior notes due August 15, 2030 1,500 1,500 4.500% senior notes due April 15, 2038 1,750 1,750 5.200% senior notes due March 1, 2047 1,000 1,000 5.200% senior notes due December 1, 2047 487 487 4.700% senior notes due April 15, 2048 1,500 1,500 5.500% senior notes due February 15, 2049 1,500 1,500 4.900% senior notes due April 15, 2058 500 500 Consolidated subsidiaries: MarkWest - 4.500% - 4.875% senior notes, due 2023-2025 23 23 ANDX - 3.500% - 5.200% senior notes, due 2022-2047 45 87 Financing lease obligations (1) 9 11 Total 18,909 20,536 Unamortized debt issuance costs (102) (116) Unamortized discount/premium (236) (281) Amounts due within one year (499) (764) Total long-term debt due after one year $ 18,072 $ 19,375 (1) See Note 20 for lease information. The following table shows five years of scheduled debt payments, including payments on finance lease obligations: (In millions) 2022 $ 502 2023 1,502 2024 1,451 2025 1,701 2026 $ 1,501 Credit Agreements MPLX Credit Agreement MPLX has a $3.5 billion revolving credit facility (the “MPLX Credit Agreement”) which is set to mature on July 30, 2024. The MPLX Credit Agreement includes a letter of credit issuing capacity of $300 million and swingline capacity of $150 million. The borrowing capacity under the MPLX Credit Agreement may be increased by up to an additional $1.0 billion, subject to certain conditions, including the consent of lenders whose commitments would increase. In addition, the maturity date may be extended, for up to two additional one year periods, subject to, among other conditions, the approval of lenders holding the majority of the commitments then outstanding, provided that the commitments of any non-consenting lenders will terminate on the then-effective maturity date. Borrowings under the MPLX Credit Agreement bear interest at either the Adjusted LIBOR or the Alternate Base Rate (as defined in the MPLX Credit Agreement), at our election, plus a specified margin. MPLX is charged various fees and expenses in connection with the agreement, including administrative agent fees, commitment fees on the unused portion of the facility and fees with respect to issued and outstanding letters of credit. The applicable margins to the benchmark interest rates and certain fees fluctuate based on the credit ratings in effect from time to time on MPLX’s long-term debt. The MPLX Credit Agreement contains certain representations and warranties, affirmative and restrictive covenants and events of default that MPLX considers to be usual and customary for an agreement of this type, including a financial covenant that requires MPLX to maintain a ratio of Consolidated Total Debt as of the end of each fiscal quarter to Consolidated EBITDA (both as defined in the MPLX Credit Agreement) for the prior four fiscal quarters of no greater than 5.0 to 1.0 (or 5.5 to 1.0 for up to two fiscal quarters following certain acquisitions). Consolidated EBITDA is subject to adjustments for certain acquisitions and dispositions completed and capital projects undertaken during the relevant period. Other covenants restrict MPLX and/or certain of its subsidiaries from incurring debt, creating liens on our assets and entering into transactions with affiliates. As of December 31, 2021, MPLX was in compliance with the covenants contained in the MPLX Credit Agreement. During the year ended December 31, 2021, MPLX borrowed $4,175 million under the MPLX Credit Agreement, at a weighted average interest rate of 1.343 percent, and repaid $4,050 million of these borrowings. At December 31, 2021, MPLX had $300 million outstanding borrowings and less than $1 million in letters of credit outstanding under this facility, resulting in total availability of $3,200 million, or approximately 91 percent of the borrowing capacity . During the year ended December 31, 2020, MPLX borrowed $3,815 million under the MPLX Credit Agreement, at a weighted average interest rate of 1.49 percent, and repaid $3,640 million of these borrowings. At December 31, 2020, MPLX had $175 million outstanding borrowings and less than $1 million in letters of credit outstanding under this facility, resulting in total availability of $3,325 million, or approximately 95 percent of the borrowing capacity. Term Loan Agreement On September 26, 2019, MPLX entered into a Term Loan Agreement, which provided for a committed term loan facility for up to an aggregate of $1.0 billion. Borrowings under the Term Loan Agreement bore interest, at MPLX’s election, at either (i) the Adjusted LIBO Rate (as defined in the Term Loan Agreement) plus a margin ranging from 75.0 basis points to 100.0 basis points per annum, depending on MPLX’s credit ratings or (ii) the Alternate Base Rate (as defined in the Term Loan Agreement). On August 18, 2020, MPLX fully repaid the $1.0 billion of outstanding borrowings on the Term Loan Agreement, which resulted in the recognition of $1 million of unamortized issuance costs, which is included on the Consolidated Statements of Income as “Other financial costs.” Floating Rate Senior Notes On September 9, 2019, MPLX issued $2.0 billion aggregate principal amount of floating rate senior notes in a public offering, consisting of $1.0 billion aggregate principal amount of notes due September 2021 and $1.0 billion aggregate principal amount of notes due September 2022 (collectively, the “Floating Rate Senior Notes”). The Floating Rate Senior Notes were offered at a price to the public of 100 percent of par. The Floating Rate Senior Notes were callable, in whole or in part, at par plus accrued and unpaid interest at any time on or after September 10, 2020. The net proceeds were used to repay MPLX’s existing indebtedness and/or for general business purposes. Interest on the Floating Rate Senior Notes was payable quarterly in March, June, September and December, commencing on December 9, 2019. The interest rate applicable to the floating rate senior notes due September 2021 was LIBOR plus 0.9 percent per annum. The interest rate applicable to the floating rate senior notes due September 2022 was LIBOR plus 1.1 percent per annum. On September 14, 2020, MPLX redeemed, at par value, all of the $1.0 billion aggregate principal amount of notes due September 2021, which resulted in the recognition of $3 million of unamortized issuance costs, which is included on the Consolidated Statements of Income as “Other financial costs.” On September 3, 2021 MPLX redeemed, at par value, all of the $1.0 billion aggregate principal amount of floating rate senior notes due September 2022, which resulted in the immediate expense recognition of $2 million of unamortized debt issuance costs. These costs are included on the Consolidated Statements of Income as “Other financial costs.” This redemption was funded primarily by borrowings under the MPC Loan Agreement. Fixed Rate Senior Notes Interest on each series of MPLX LP, MarkWest and ANDX senior notes is payable semi-annually in arrears, according to the table below. Senior Notes Interest payable semi-annually in arrears 3.500% senior notes due December 1, 2022 June 1 st and December 1 st 3.375% senior notes due March 15, 2023 March 15 th and September 15 th 4.500% senior notes due July 15, 2023 January 15 th and July 15 th 4.875% senior notes due December 1, 2024 June 1 st and December 1 st 4.000% senior notes due February 15, 2025 February 15 th and August 15 th 4.875% senior notes due June 1, 2025 June 1 st and December 1 st 1.750% senior notes due March 1, 2026 March 1 st and September 1 st 4.125% senior notes due March 1, 2027 March 1 st and September 1 st 4.250% senior notes due December 1, 2027 June 1 st and December 1 st 4.000% senior notes due March 15, 2028 March 15 th and September 15 th 4.800% senior notes due February 15, 2029 February 15 th and August 15 th 2.650% senior notes due August 15, 2030 February 15 th and August 15 th 4.500% senior notes due April 15, 2038 April 15 th and October 15 th 5.200% senior notes due March 1, 2047 March 1 st and September 1 st 5.200% senior notes due December 1, 2047 June 1 st and December 1 st 4.700% senior notes due April 15, 2048 April 15 th and October 15 th 5.500% senior notes due February 15, 2049 February 15 th and August 15 th 4.900% senior notes due April 15, 2058 April 15 th and October 15 th On January 15, 2021 MPLX redeemed all of the $750 million outstanding aggregate principal amount of 5.250 percent senior notes, due January 15, 2025, including approximately $42 million aggregate principal amount of senior notes issued by ANDX, at a price equal to 102.625 percent of the principal amount. The payment of $20 million related to the note premium, offset by the immediate expense recognition of $12 million of unamortized debt premium and issuance costs, resulted in a loss on extinguishment of debt of $8 million that is included on the Consolidated Statements of Income as “Other financial costs.” On August 18, 2020, MPLX issued $3.0 billion aggregate principal amount of senior notes in a public offering, consisting of $1.5 billion aggregate principal amount of 1.750 percent senior notes due March 2026 and $1.5 billion aggregate principal amount of 2.650 percent senior notes due August 2030 (collectively, the “August 2020 New Senior Notes”). The August 2020 New Senior Notes were offered at a price to the public of 99.785 percent and 99.913 percent of par, respectively. The net proceeds were used to repay the $1.0 billion of outstanding borrowings under the MPLX Term Loan Agreement; to repay the $1.0 billion aggregate principal amount of floating rate notes due September 2021; to redeem all of the $450 million aggregate principal amount of 6.375 percent senior notes due May 2024, $69 million of which was issued by ANDX; and to redeem all of the $300 million aggregate principal amount of 6.250 percent senior notes due October 2022, of which $34 million was issued by ANDX. Proceeds were also used to reduce amounts outstanding under the MPLX Credit Agreement at the time.

Revenue Revenue

Revenue Revenue	12 Months Ended
	Dec. 31, 2021
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 years ended December 31, 2021, 2020 and 2019: 2021 (In millions) L&S G&P Total Revenues and other income: Service revenue $ 310 $ 2,003 $ 2,313 Service revenue - related parties 3,608 20 3,628 Service revenue - product related — 345 345 Product sales 4 1,586 1,590 Product sales - related parties 10 135 145 Total revenues from contracts with customers $ 3,932 $ 4,089 8,021 Non-ASC 606 revenue (1) 2,006 Total revenues and other income $ 10,027 2020 (In millions) L&S G&P Total Revenues and other income: Service revenue $ 333 $ 2,064 $ 2,397 Service revenue - related parties 3,556 24 3,580 Service revenue - product related — 155 155 Product sales 39 597 636 Product sales - related parties 12 116 128 Total revenues from contracts with customers $ 3,940 $ 2,956 6,896 Non-ASC 606 revenue (1) 673 Total revenues and other income $ 7,569 2019 (In millions) L&S G&P Total Revenues and other income: Service revenue $ 346 $ 2,152 $ 2,498 Service revenue - related parties 3,419 36 3,455 Service revenue - product related — 140 140 Product sales 65 741 806 Product sales - related parties 26 116 142 Total revenues from contracts with customers $ 3,856 $ 3,185 7,041 Non-ASC 606 revenue (1) 2,000 Total revenues and other income $ 9,041 (1) Non-ASC 606 Revenue includes rental income, sales-type lease revenue, income/(loss) from equity method investments, derivative gains and losses, mark-to-market adjustments, 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 years ended December 31, 2021 and 2020: (In millions) Balance at December 31, 2020 (1) Additions/ (Deletions) Revenue Recognized (2) Balance at December 31, 2021 (1) Contract assets $ 40 $ (15) $ — $ 25 Long-term contract assets 2 — — 2 Deferred revenue 37 56 (37) 56 Deferred revenue - related parties 91 75 (106) 60 Long-term deferred revenue 119 16 — 135 Long-term deferred revenue - related parties 48 (17) — 31 Long-term contract liabilities $ 6 $ (1) $ — $ 5 (In millions) Balance at December 31, 2019 (1) Additions/ (Deletions) Revenue Recognized (2) Balance at December 31, 2020 (1) Contract assets $ 39 $ 3 $ (2) $ 40 Long-term contract assets — 2 — 2 Deferred revenue 23 22 (8) 37 Deferred revenue - related parties 53 121 (83) 91 Long-term deferred revenue 90 29 — 119 Long-term deferred revenue - related parties 55 (7) — 48 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 December 31, 2021, the amounts allocated to contract assets and contract liabilities on the Consolidated Balance Sheets are $281 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 $ 1,850 2023 1,725 2024 1,592 2025 1,507 2026 and thereafter 3,283 Total revenue on remaining performance obligations (1)(2)(3) $ 9,957 (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, see further discussion about leases in Note 20. (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	12 Months Ended
	Dec. 31, 2021
Supplemental Cash Flow Information [Abstract]
Supplemental Cash Flow Information	Supplemental Cash Flow Information (In millions) 2021 2020 2019 Net cash provided by operating activities included: Interest paid (net of amounts capitalized) $ 812 $ 821 $ 835 Income taxes paid 4 2 1 Cash paid for amounts included in the measurement of lease liabilities Payments on operating leases 79 87 85 Interest payment under finance lease obligations — 1 1 Net cash provided by financing activities included: Principal payments under finance lease obligations 2 9 5 Non-cash investing and financing activities: Net transfers of property, plant and equipment from materials and supplies inventories 1 — 2 MPLX terminal lease classification change — — 21 ROU assets obtained in exchange for new operating lease obligations 20 17 26 ROU assets obtained in exchange for new finance lease obligations — 1 4 Fair value of common units redeemed for Wholesale Exchange — 340 — Contribution - common units issued (1) $ — $ — $ 7,722 (1) For 2019, includes limited partner units issued to MPC and public unitholders as consideration in the Merger. See Note 4. The Consolidated Statements of Cash Flows exclude changes to the Consolidated Balance Sheets that did not affect cash. The following is the change of additions to property, plant and equipment related to capital accruals: (In millions) 2021 2020 2019 (Decrease)/increase in capital accruals $ 11 $ (244) $ (146)

Leases Leases (Notes)

Leases Leases (Notes)	12 Months Ended
	Dec. 31, 2021
Leases [Abstract]
Lessee, Operating Leases	Lessee We lease a wide variety of facilities and equipment under leases from third parties, including land and building space, office and field equipment, storage facilities and transportation equipment, while our related party leases primarily relate to ground leases associated with our refining logistics assets. Our remaining lease terms range from less than one one The components of lease cost were as follows: 2021 2020 2019 (In millions) Related Party Third Related Third Related Third Components of lease costs: Operating lease costs $ 15 $ 71 $ 14 $ 78 $ 14 $ 75 Finance lease cost: Amortization of ROU assets — 2 — 3 — 5 Interest on lease liabilities — 1 — 1 — 1 Total finance lease cost — 3 — 4 — 6 Variable lease cost — 15 1 10 1 11 Short-term lease cost — 31 — 52 — 80 Total lease cost $ 15 $ 120 $ 15 $ 144 $ 15 $ 172 Supplemental balance sheet data related to leases were as follows: December 31, 2021 December 31, 2020 (In millions, except % and years) Related Party Third Party Related Party Third Party Operating leases Assets Right of use assets $ 229 $ 268 $ 231 $ 309 Liabilities Operating lease liabilities 1 59 1 63 Long-term operating lease liabilities 228 205 229 244 Total operating lease liabilities $ 229 $ 264 $ 230 $ 307 Weighted average remaining lease term 45.2 years 8.3 years 46.2 years 8.0 years Weighted average discount rate 5.8 % 4.1 % 5.8 % 4.3 % Finance leases Assets Property, plant and equipment, gross $ 11 $ 17 Less: Accumulated depreciation 4 8 Property, plant and equipment, net 7 9 Liabilities Long-term debt due within one year 2 2 Long-term debt 7 9 Total finance lease liabilities $ 9 $ 11 Weighted average remaining lease term 19.4 years 16.9 years Weighted average discount rate 6.0 % 6.0 % As of December 31, 2021, maturities of lease liabilities for operating lease obligations and finance lease obligations having initial or remaining non-cancellable lease terms in excess of one year are as follows: (In millions) Related Party Operating Third Party Operating Finance 2022 $ 15 $ 68 $ 2 2023 15 59 2 2024 14 38 1 2025 14 21 1 2026 14 18 1 2027 and thereafter 575 109 8 Gross lease payments 647 313 15 Less: Imputed interest 418 49 6 Total lease liabilities $ 229 $ 264 $ 9
Lessee, Finance Leases	Lessee We lease a wide variety of facilities and equipment under leases from third parties, including land and building space, office and field equipment, storage facilities and transportation equipment, while our related party leases primarily relate to ground leases associated with our refining logistics assets. Our remaining lease terms range from less than one one The components of lease cost were as follows: 2021 2020 2019 (In millions) Related Party Third Related Third Related Third Components of lease costs: Operating lease costs $ 15 $ 71 $ 14 $ 78 $ 14 $ 75 Finance lease cost: Amortization of ROU assets — 2 — 3 — 5 Interest on lease liabilities — 1 — 1 — 1 Total finance lease cost — 3 — 4 — 6 Variable lease cost — 15 1 10 1 11 Short-term lease cost — 31 — 52 — 80 Total lease cost $ 15 $ 120 $ 15 $ 144 $ 15 $ 172 Supplemental balance sheet data related to leases were as follows: December 31, 2021 December 31, 2020 (In millions, except % and years) Related Party Third Party Related Party Third Party Operating leases Assets Right of use assets $ 229 $ 268 $ 231 $ 309 Liabilities Operating lease liabilities 1 59 1 63 Long-term operating lease liabilities 228 205 229 244 Total operating lease liabilities $ 229 $ 264 $ 230 $ 307 Weighted average remaining lease term 45.2 years 8.3 years 46.2 years 8.0 years Weighted average discount rate 5.8 % 4.1 % 5.8 % 4.3 % Finance leases Assets Property, plant and equipment, gross $ 11 $ 17 Less: Accumulated depreciation 4 8 Property, plant and equipment, net 7 9 Liabilities Long-term debt due within one year 2 2 Long-term debt 7 9 Total finance lease liabilities $ 9 $ 11 Weighted average remaining lease term 19.4 years 16.9 years Weighted average discount rate 6.0 % 6.0 % As of December 31, 2021, maturities of lease liabilities for operating lease obligations and finance lease obligations having initial or remaining non-cancellable lease terms in excess of one year are as follows: (In millions) Related Party Operating Third Party Operating Finance 2022 $ 15 $ 68 $ 2 2023 15 59 2 2024 14 38 1 2025 14 21 1 2026 14 18 1 2027 and thereafter 575 109 8 Gross lease payments 647 313 15 Less: Imputed interest 418 49 6 Total lease liabilities $ 229 $ 264 $ 9
Lessor, Operating Leases	Lessor Based on the terms of fee-based transportation and storage services agreements with MPC and third parties, MPLX is considered to be the lessor under several operating lease arrangements in accordance with GAAP. These agreements have remaining terms ranging from less than one year to 8 years with renewal options ranging from one year to 5 years, with some agreements having multiple renewal options. We are also considered to be the lessor under operating lease agreements related to certain fee-based natural gas gathering, transportation and processing agreements. MPLX’s primary natural gas lease operations relate to a natural gas gathering agreement in the Marcellus Shale for which it earns a fixed-fee for providing gathering services to a single producer using a dedicated gathering system. As the gathering system is expanded, the fixed-fee charged to the producer is adjusted to include the additional gathering assets in the lease. The primary term of the natural gas gathering arrangement expires in 2038 and will continue thereafter on a year-to-year basis until terminated by either party. Other significant natural gas implicit leases relate to a natural gas processing agreement in the Marcellus Shale and a natural gas processing agreement in the Southern Appalachia region for which MPLX earns minimum monthly fees for providing processing services to a single producer using a dedicated processing plant. The primary term of these natural gas processing agreements expires during 2027 and 2028, respectively, these contracts will continue thereafter on a year-to-year basis until terminated by either party. MPLX did not elect to use the practical expedient to combine lease and non-lease components for lessor arrangements. The tables below represent the portion of the contract allocated to the lease component based on relative standalone selling price. We elected the practical expedient to carry forward historical classification conclusions until a modification of an existing agreement occurs. Once a modification occurs, the amended agreement is required to be assessed under ASC 842, to determine whether a reclassification of the lease is required. During the second quarter of 2021 and during the first quarter of 2020, reimbursements for projects and changes to minimum volume commitments at certain L&S locations were agreed to between MPLX and MPC. These reimbursements and minimum volume commitments relate to the storage, transportation and terminal services agreements between MPLX and MPC at these locations and required the embedded leases within these agreements to be reassessed under ASC 842. As a result of the reassessment, certain leases were reclassified from an operating lease to a sales-type lease. Accordingly, the underlying assets previously shown on the Consolidated Balance Sheets associated with the sales-type leases were derecognized and the net investment in the lease (i.e., the sum of the present value of the future lease payments and the unguaranteed residual value of the assets) was recorded as a lease receivable during the respective periods. See Note 6 for the location of lease receivables and unguaranteed residual assets on the Consolidated Balance Sheets. The difference between the net book value of the underlying assets and the net investment in the lease has been recorded as a “Contribution from MPC” in the Consolidated Statements of Equity given the impacted storage and terminal services agreements are related to a common control transaction. During the second quarter of 2021, MPLX derecognized approximately $421 million of property, plant and equipment, recorded a lease receivable of approximately $519 million, recorded an unguaranteed residual asset of approximately $14 million with the difference recorded as a deemed “Contribution from MPC” of $112 million. During the first quarter of 2020, MPLX derecognized approximately $171 million of property, plant and equipment, recorded a lease receivable of approximately $370 million, recorded an unguaranteed residual asset of approximately $10 million and a “Contribution from MPC” of $209 million. Lease revenues included on the Consolidated Statements of Income during 2021, 2020 and 2019 were as follows: 2021 2020 2019 (In millions) Related Party Third Related Party Third Related Party Third Operating leases: Rental income $ 743 $ 376 $ 952 $ 398 $ 1,196 $ 388 Sales-type leases: Profit/(loss) recognized at the commencement date — — — — — — Interest income (Sales-type rental revenue- fixed minimum) 431 — 151 — 6 — Interest income (Revenue from variable lease payments) 4 — 1 — 1 — Sales-type lease revenue $ 435 $ — $ 152 $ — $ 7 $ — The following is a schedule of minimum future rental revenue on the non-cancellable operating leases as of December 31, 2021: (In millions) Related Party Third Party Total 2022 $ 632 $ 213 $ 845 2023 563 207 770 2024 514 204 718 2025 511 171 682 2026 504 142 646 2027 and thereafter 308 1,299 1,607 Total minimum future rentals $ 3,032 $ 2,236 $ 5,268 The following is a schedule of minimum future revenue on sales-type leases as of December 31, 2021: (In millions) Related Party 2022 $ 544 2023 544 2024 538 2025 525 2026 422 2027 and thereafter 595 Total minimum future rentals 3,168 Less: present value discount 2,232 Lease receivable $ 936 The following schedule summarizes MPLX’s investment in assets held under operating lease by major classes as of December 31, 2021 and 2020: December 31, (In millions) 2021 2020 Pipelines $ 953 $ 834 Refining logistics 1,146 1,680 Terminals 1,290 1,276 Marine 129 129 Gathering and transportation 991 990 Processing and fractionation 867 867 Land, building and other 176 171 Total property, plant and equipment 5,552 5,947 Less: accumulated depreciation 2,042 2,007 Property, plant and equipment, net $ 3,510 $ 3,940 See Note 6 for additional information on where related party lease assets are recorded in the Consolidated Balance Sheets. At December 31, 2021 and 2020, third-party lease assets were less than $1 million and are included within the “Receivables, net” and “Other noncurrent assets” captions within the Consolidated Balance Sheets.
Lessor, Sales-type Leases	Lessor Based on the terms of fee-based transportation and storage services agreements with MPC and third parties, MPLX is considered to be the lessor under several operating lease arrangements in accordance with GAAP. These agreements have remaining terms ranging from less than one year to 8 years with renewal options ranging from one year to 5 years, with some agreements having multiple renewal options. We are also considered to be the lessor under operating lease agreements related to certain fee-based natural gas gathering, transportation and processing agreements. MPLX’s primary natural gas lease operations relate to a natural gas gathering agreement in the Marcellus Shale for which it earns a fixed-fee for providing gathering services to a single producer using a dedicated gathering system. As the gathering system is expanded, the fixed-fee charged to the producer is adjusted to include the additional gathering assets in the lease. The primary term of the natural gas gathering arrangement expires in 2038 and will continue thereafter on a year-to-year basis until terminated by either party. Other significant natural gas implicit leases relate to a natural gas processing agreement in the Marcellus Shale and a natural gas processing agreement in the Southern Appalachia region for which MPLX earns minimum monthly fees for providing processing services to a single producer using a dedicated processing plant. The primary term of these natural gas processing agreements expires during 2027 and 2028, respectively, these contracts will continue thereafter on a year-to-year basis until terminated by either party. MPLX did not elect to use the practical expedient to combine lease and non-lease components for lessor arrangements. The tables below represent the portion of the contract allocated to the lease component based on relative standalone selling price. We elected the practical expedient to carry forward historical classification conclusions until a modification of an existing agreement occurs. Once a modification occurs, the amended agreement is required to be assessed under ASC 842, to determine whether a reclassification of the lease is required. During the second quarter of 2021 and during the first quarter of 2020, reimbursements for projects and changes to minimum volume commitments at certain L&S locations were agreed to between MPLX and MPC. These reimbursements and minimum volume commitments relate to the storage, transportation and terminal services agreements between MPLX and MPC at these locations and required the embedded leases within these agreements to be reassessed under ASC 842. As a result of the reassessment, certain leases were reclassified from an operating lease to a sales-type lease. Accordingly, the underlying assets previously shown on the Consolidated Balance Sheets associated with the sales-type leases were derecognized and the net investment in the lease (i.e., the sum of the present value of the future lease payments and the unguaranteed residual value of the assets) was recorded as a lease receivable during the respective periods. See Note 6 for the location of lease receivables and unguaranteed residual assets on the Consolidated Balance Sheets. The difference between the net book value of the underlying assets and the net investment in the lease has been recorded as a “Contribution from MPC” in the Consolidated Statements of Equity given the impacted storage and terminal services agreements are related to a common control transaction. During the second quarter of 2021, MPLX derecognized approximately $421 million of property, plant and equipment, recorded a lease receivable of approximately $519 million, recorded an unguaranteed residual asset of approximately $14 million with the difference recorded as a deemed “Contribution from MPC” of $112 million. During the first quarter of 2020, MPLX derecognized approximately $171 million of property, plant and equipment, recorded a lease receivable of approximately $370 million, recorded an unguaranteed residual asset of approximately $10 million and a “Contribution from MPC” of $209 million. Lease revenues included on the Consolidated Statements of Income during 2021, 2020 and 2019 were as follows: 2021 2020 2019 (In millions) Related Party Third Related Party Third Related Party Third Operating leases: Rental income $ 743 $ 376 $ 952 $ 398 $ 1,196 $ 388 Sales-type leases: Profit/(loss) recognized at the commencement date — — — — — — Interest income (Sales-type rental revenue- fixed minimum) 431 — 151 — 6 — Interest income (Revenue from variable lease payments) 4 — 1 — 1 — Sales-type lease revenue $ 435 $ — $ 152 $ — $ 7 $ — The following is a schedule of minimum future rental revenue on the non-cancellable operating leases as of December 31, 2021: (In millions) Related Party Third Party Total 2022 $ 632 $ 213 $ 845 2023 563 207 770 2024 514 204 718 2025 511 171 682 2026 504 142 646 2027 and thereafter 308 1,299 1,607 Total minimum future rentals $ 3,032 $ 2,236 $ 5,268 The following is a schedule of minimum future revenue on sales-type leases as of December 31, 2021: (In millions) Related Party 2022 $ 544 2023 544 2024 538 2025 525 2026 422 2027 and thereafter 595 Total minimum future rentals 3,168 Less: present value discount 2,232 Lease receivable $ 936 The following schedule summarizes MPLX’s investment in assets held under operating lease by major classes as of December 31, 2021 and 2020: December 31, (In millions) 2021 2020 Pipelines $ 953 $ 834 Refining logistics 1,146 1,680 Terminals 1,290 1,276 Marine 129 129 Gathering and transportation 991 990 Processing and fractionation 867 867 Land, building and other 176 171 Total property, plant and equipment 5,552 5,947 Less: accumulated depreciation 2,042 2,007 Property, plant and equipment, net $ 3,510 $ 3,940 See Note 6 for additional information on where related party lease assets are recorded in the Consolidated Balance Sheets. At December 31, 2021 and 2020, third-party lease assets were less than $1 million and are included within the “Receivables, net” and “Other noncurrent assets” captions within the Consolidated Balance Sheets.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	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 December 31, 2021 and 2020, accrued liabilities for remediation totaled $23 million and $17 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. At December 31, 2021 and 2020, there were no balances with MPC for indemnification of environmental costs. 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 December 31, 2021, our maximum potential undiscounted payments under the Contingent Equity Contribution Agreement were approximately $230 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 specified 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 – At December 31, 2021, MPLX’s contractual commitments to acquire property, plant and equipment totaled $116 million. These commitments were primarily related to G&P plant expansions. In addition, from time to time and in the ordinary course of business, MPLX and its affiliates provide guarantees of MPLX’s subsidiaries payment and performance obligations in the G&P segment. Certain natural gas processing and gathering arrangements require MPLX to construct new natural gas processing plants, natural gas gathering pipelines and NGL pipelines and contain certain fees and charges if specified construction milestones are not achieved for reasons other than force majeure. In certain cases, certain producers may have the right to cancel the processing arrangements if there are significant delays that are not due to force majeure. As of December 31, 2021, management does not believe there are any indications that MPLX will not be able to meet the construction milestones, that force majeure does not apply or that such fees and charges will otherwise be triggered. Other Contractual Obligations – MPLX executed various third party transportation and terminalling agreements that obligate us to minimum volume, throughput or payment commitments over the remaining terms of the agreements, which range from one (In millions) 2022 $ 117 2023 155 2024 146 2025 124 2026 111 2027 and thereafter 310 Total $ 963

Description of Business and B_2

Description of Business and Basis of Presentation (Policies)	12 Months Ended
	Dec. 31, 2021
Limited Liability Company or Limited Partnership, Business Organization and Operations [Abstract]
Basis of presentation	Basis of Presentation – The accompanying consolidated financial statements of MPLX have been prepared in accordance with GAAP. The 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 a VIE in which MPLX exercises significant influence but does not control and is not the primary beneficiary are also accounted for using the equity method. In relation to the Merger described above and in Note 4, ANDX’s assets, liabilities and results of operations prior to the Merger are collectively included in what we refer to as the “Predecessor” from October 1, 2018, which was the date that MPC acquired Andeavor. MPLX’s acquisition of ANDX is considered a transfer between entities under common control due to MPC’s relationship with ANDX prior to the Merger. As an entity under common control with MPC, MPLX recorded the assets acquired and liabilities assumed on its consolidated balance sheets at MPC’s historical carrying value. For the acquiring entity, transfers of businesses between entities under common control require prior periods to be retrospectively adjusted for those dates that the entity was under common control. Accordingly, the accompanying financial statements and related notes of MPLX LP have been retrospectively adjusted to include the historical results of ANDX beginning October 1, 2018.

Summary of Principal Accounti_2

Summary of Principal Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Use of estimates	Use of Estimates – The preparation of financial statements in accordance with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amounts of
Revenue recognition	Revenue Recognition – Revenue is measured based on consideration specified in a contract with a customer. MPLX recognizes revenue when it satisfies a performance obligation by transferring control over a product or providing services to a customer. MPLX enters into a variety of contract types in order to generate “Product sales” and “Service revenue.” MPLX provides services under the following types of arrangements: • Fee-based arrangements – Under fee-based arrangements, MPLX receives a fee or fees for one or more of the following services: gathering, processing and transportation of natural gas; gathering, transportation, fractionation, exchange and storage of NGLs; and transportation, terminalling, storage and distribution of crude oil, refined products and other hydrocarbon-based products. The revenue MPLX earns from these arrangements is generally directly related to the volume of natural gas, NGLs, refined products or crude oil that is handled by or flows through MPLX’s systems and facilities and is not normally directly dependent on commodity prices. In certain cases, MPLX’s arrangements provide for minimum volume commitments. • Fee-based arrangements are reported as “Service revenue” on the Consolidated Statements of Income. Revenue is recognized over time as services are performed. In certain instances when specifically stated in the contract terms, MPLX purchases product after fee-based services have been provided. Revenue from the sale of products purchased after services are provided is reported as “Product sales” on the Consolidated Statements of Income and recognized on a gross basis, as MPLX takes control of the product and is the principal in the transaction. • Percent-of-proceeds arrangements – Under percent-of-proceeds arrangements, MPLX gathers and processes natural gas on behalf of producers; sells the resulting residue gas, condensate and NGLs at market prices; and remits to producers an agreed-upon percentage of the proceeds. In other cases, instead of remitting cash payments to the producer, MPLX delivers an agreed-upon percentage of the residue gas and NGLs to the producer (take-in-kind arrangements) and sells the volumes MPLX retains to third parties or related parties. Revenue is recognized on a net basis when MPLX acts as an agent and does not have control of the gross amount of gas and/or NGLs prior to it being sold. Percent-of-proceeds revenue is reported as “Service revenue - product related” on the Consolidated Statements of Income. • Keep-whole arrangements – Under keep-whole arrangements, MPLX gathers natural gas from the producer, processes the natural gas and sells the resulting condensate and NGLs to third parties at market prices. Because the extraction of the condensate and NGLs from the natural gas during processing reduces the Btu content of the natural gas, MPLX must either purchase natural gas at market prices for return to producers or make cash payment to the producers equal to the value of the energy content of this natural gas. Certain keep-whole arrangements also have provisions that require MPLX to share a percentage of the keep-whole profits with the producers based on the oil to gas ratio or the NGL to gas ratio. “Service revenue - product related” is recorded based on the value of the NGLs received on the date the services are performed. Natural gas purchased to return to the producer and shared NGL profits are recorded as a reduction of “Service revenue - product related” on the Consolidated Statements of Income on the date the services are performed. Sales of NGLs under these arrangements are reported as “Product sales” on the Consolidated Statements of Income and are reported on a gross basis as MPLX is the principal in the arrangement and controls the product prior to sale. The sale of the NGLs may occur shortly after services are performed at the tailgate of the plant, or after a period of time as determined by MPLX. • Purchase arrangements – Under purchase arrangements, MPLX purchases natural gas at either the wellhead or the tailgate of a plant. MPLX then gathers and delivers the natural gas to pipelines where MPLX may resell the natural gas. Wellhead purchase arrangements represent an arrangement with a supplier and are recorded in “Purchased product costs.” Often, MPLX earns fees for services performed prior to taking control of the product in these arrangements and “Service revenue” is recorded for these fees. Revenue generated from the sale of product obtained in tailgate purchase arrangements is reported as “Product sales” on the Consolidated Statements of Income and is recognized on a gross basis as MPLX purchases and takes control of the product prior to sale and is the principal in the transaction. In many cases, MPLX provides services under contracts that contain a combination of more than one of the arrangements described above. When fees are charged (in addition to product received) under percent-of-proceeds arrangements, keep-whole arrangements or purchase arrangements, MPLX records such fees as “Service revenue” on the Consolidated Statements of Income. The terms of MPLX’s contracts vary based on gas quality conditions, the competitive environment when the contracts are signed, and customer requirements. Performance obligations are determined based on the specific terms of the arrangements, economics of the geographical regions, and the services offered and whether they are deemed distinct. MPLX allocates the consideration earned between the performance obligations based on the stand-alone selling price when multiple performance obligations are identified. Revenue from MPLX’s service arrangements will generally be recognized over time as the performance obligation is satisfied as services are provided. MPLX has elected to use the output measure of progress to recognize revenue based on the units delivered, processed or transported. The transaction price has fixed components related to minimum volume commitments and variable components, which are primarily dependent on volumes. Variable consideration will generally not be estimated at contract inception as the transaction price is specifically allocable to the services provided each period. In instances in which tiered pricing structures do not reflect our efforts to perform, MPLX will estimate variable consideration at contract inception. “Product sales” will be recognized at a point in time when control of the product transfers to the customer. Minimum volume commitments may create contract liabilities or deferred credits if current period payments can be used for future services. Breakage is estimated and recognized into service revenue in instances where it is probable the customer will not use the credit in future periods. Amounts billed to customers for shipping and handling, electricity, and other costs to perform services are included in “Service revenue” on the Consolidated Statements of Income. Shipping and handling costs associated with product sales are included in “Purchased product costs” on the Consolidated Statements of Income. Facility expenses, costs of revenues and depreciation represent those expenses related to operating our various facilities and are necessary to provide both “Product sales” and “Service revenue.” Customers usually pay monthly based on the products purchased or services performed that month. Taxes collected from customers and remitted to the appropriate taxing authority are excluded from revenue.
Revenue and expense accruals	Revenue and Expense Accruals – MPLX routinely makes accruals based on estimates for both revenues and expenses due to the timing of compiling billing information, receiving certain third-party information and reconciling MPLX’s records with those of third parties. The delayed information from third parties includes, among other things, actual volumes purchased, transported or sold, adjustments to inventory and invoices for purchases, actual natural gas and NGL deliveries, and other operating expenses. MPLX makes accruals to reflect estimates for these items based on its internal records and information from third parties. Estimated accruals are adjusted when actual information is received from third parties and MPLX’s internal records have been reconciled.
Cash and Cash Equivalents, Policy	Cash and Cash Equivalents – Cash and cash equivalents include cash on hand and on deposit and investments in highly liquid debt instruments with initial maturities of three months or less.
Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy	Restricted Cash – Restricted cash consists of cash and investments that must be maintained as collateral for letters of credit issued to certain third-party producer customers. The balances will be outstanding until certain capital projects are completed and the third party releases the restriction. Restricted cash also consists of cash advances to be used for the operation and maintenance of an operated pipeline system. MPLX had no restricted cash as of the years ended December 31, 2021 or 2020.
Receivables	Receivables – Receivables primarily consist of customer accounts receivable, which are recorded at the invoiced amount and generally do not bear interest. Allowances for doubtful accounts are generally recorded when it becomes probable that the receivable will not be collected and are recorded to bad debt expense. We review the allowance quarterly with past-due balances over 90 days and other higher-risk amounts being reviewed individually
Lessee, Leases	Leases – As part of the adoption of ASU No. 2016-02, Leases (“ASC 842”), we elected the package of practical expedients permitted under the transition guidance within the new standard, which among other things, allowed us to grandfather the historical accounting conclusions until a reassessment event is present. We also elected the practical expedient to not recognize short-term leases on the balance sheet, the practical expedient related to right of way permits and land easements which allows us to carry forward our accounting treatment for those existing agreements, and the practical expedient to combine lease and non-lease components for the majority of our underlying classes of assets except for our third-party contractor service and equipment agreements and boat and barge equipment agreements in which we are the lessee. We did not elect the practical expedient to combine lease and non-lease components for arrangements in which we are the lessor. In instances where the practical expedient was not elected, lease and non-lease consideration is allocated based on relative standalone selling price. Right of use (“ROU”) assets represent our right to use an underlying asset in which we obtain substantially all of the economic benefits and the right to direct the use of the asset during the lease term. Lease liabilities represent our obligation to make lease payments arising from the lease. Operating lease ROU assets and lease liabilities are recognized at the commencement date based on the present value of lease payments over the lease term. We recognize ROU assets and lease liabilities on the balance sheet for leases with a lease term of greater than one year. Payments that are not fixed at the commencement of the lease are considered variable and are excluded from the ROU asset and lease liability calculations. In the measurement of our ROU assets and lease liabilities, the fixed lease payments in the agreement are discounted using a secured incremental borrowing rate for a term similar to the duration of the lease, as our leases do not provide implicit rates. Operating lease expense is recognized on a straight-line basis over the lease term.
Lessor, Leases	Leases – As part of the adoption of ASU No. 2016-02, Leases (“ASC 842”), we elected the package of practical expedients permitted under the transition guidance within the new standard, which among other things, allowed us to grandfather the historical accounting conclusions until a reassessment event is present. We also elected the practical expedient to not recognize short-term leases on the balance sheet, the practical expedient related to right of way permits and land easements which allows us to carry forward our accounting treatment for those existing agreements, and the practical expedient to combine lease and non-lease components for the majority of our underlying classes of assets except for our third-party contractor service and equipment agreements and boat and barge equipment agreements in which we are the lessee. We did not elect the practical expedient to combine lease and non-lease components for arrangements in which we are the lessor. In instances where the practical expedient was not elected, lease and non-lease consideration is allocated based on relative standalone selling price. Right of use (“ROU”) assets represent our right to use an underlying asset in which we obtain substantially all of the economic benefits and the right to direct the use of the asset during the lease term. Lease liabilities represent our obligation to make lease payments arising from the lease. Operating lease ROU assets and lease liabilities are recognized at the commencement date based on the present value of lease payments over the lease term. We recognize ROU assets and lease liabilities on the balance sheet for leases with a lease term of greater than one year. Payments that are not fixed at the commencement of the lease are considered variable and are excluded from the ROU asset and lease liability calculations. In the measurement of our ROU assets and lease liabilities, the fixed lease payments in the agreement are discounted using a secured incremental borrowing rate for a term similar to the duration of the lease, as our leases do not provide implicit rates. Operating lease expense is recognized on a straight-line basis over the lease term.
Inventories	Inventories – Inventories consist of materials and supplies to be used in operations, line fill and other NGLs. Cost for materials and supplies are determined primarily using the weighted-average cost method. Inventories are valued at the lower of cost or market value.
Imbalances	Imbalances – Within our pipelines and storage assets, we experience volume gains and losses due to pressure and temperature changes, evaporation and variances in meter readings and other measurement methods. Until settled, positive imbalances are recorded as other current assets and negative imbalances are recorded as accounts payable. Positive and negative product imbalances are settled in cash, settled by physical delivery of gas from a different source, or tracked and settled in the future.
Property, plant and equipment	Property, Plant and Equipment – Property, plant and equipment are recorded at cost and depreciated on a straight-line basis over the estimated useful lives of the assets. Expenditures that extend the useful lives of assets are capitalized. Such assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. If the sum of the expected undiscounted future cash flows from the use of the asset and its eventual disposition is less than the carrying amount of the asset, an impairment assessment is performed and the excess of the book value over the fair value is recorded as an impairment loss. When items of property, plant and equipment are sold or otherwise disposed of, any gains or losses are reported on the Consolidated Statements of Income. Gains on the disposal of property, plant and equipment are recognized when they occur, which is generally at the time of closing. If a loss on disposal is expected, such losses are recognized when the assets are classified as held for sale.
Intangibles	Goodwill and Intangibles – Goodwill represents the excess of the purchase price over the estimated fair value of the net assets acquired in the acquisition of a business. Goodwill is not amortized, but rather is tested for impairment annually and when events or changes in circumstances indicate that the fair value of a reporting unit with goodwill has been reduced below carrying value. The impairment test requires allocating goodwill and other assets and liabilities to reporting units. The fair value of each reporting unit is determined using an income and/or market approach which is compared to the carrying value of the reporting unit. The fair value under the income approach is calculated using the expected present value of future cash flows method. Significant assumptions used in the cash flow forecasts include future operating performance, future volumes, discount rates, and future capital requirements. If the fair value of the reporting unit is less than the carrying value, including goodwill, the excess, if any, of the book value over the fair value of the reporting unit up to the amount of goodwill recorded is charged to net income as an impairment expense. See Note 14 for further details. Amortization of intangibles with definite lives is calculated using the straight-line method, which is reflective of the benefit pattern in which the estimated economic benefit is expected to be received over the estimated useful life of the intangible asset. Intangibles subject to amortization are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the intangible may not be recoverable. If the sum of the expected undiscounted future cash flows related to the asset is less than the carrying amount of the asset, an impairment loss is recognized based on the fair value of the asset.
Goodwill	Goodwill and Intangibles – Goodwill represents the excess of the purchase price over the estimated fair value of the net assets acquired in the acquisition of a business. Goodwill is not amortized, but rather is tested for impairment annually and when events or changes in circumstances indicate that the fair value of a reporting unit with goodwill has been reduced below carrying value. The impairment test requires allocating goodwill and other assets and liabilities to reporting units. The fair value of each reporting unit is determined using an income and/or market approach which is compared to the carrying value of the reporting unit. The fair value under the income approach is calculated using the expected present value of future cash flows method. Significant assumptions used in the cash flow forecasts include future operating performance, future volumes, discount rates, and future capital requirements. If the fair value of the reporting unit is less than the carrying value, including goodwill, the excess, if any, of the book value over the fair value of the reporting unit up to the amount of goodwill recorded is charged to net income as an impairment expense. See Note 14 for further details. Amortization of intangibles with definite lives is calculated using the straight-line method, which is reflective of the benefit pattern in which the estimated economic benefit is expected to be received over the estimated useful life of the intangible asset. Intangibles subject to amortization are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the intangible may not be recoverable. If the sum of the expected undiscounted future cash flows related to the asset is less than the carrying amount of the asset, an impairment loss is recognized based on the fair value of the asset.
Other taxes	Other Taxes – Other taxes primarily include real estate taxes.
Environmental costs	Environmental Costs – Environmental expenditures are capitalized if the costs mitigate or prevent future contamination or if the costs improve environmental safety or efficiency of the existing assets. MPLX recognizes remediation costs and penalties when the responsibility to remediate is probable and the amount of associated costs can be reasonably estimated. The timing of remediation accruals coincides with completion of a feasibility study or the commitment to a formal plan of action. Remediation liabilities are accrued based on estimates of known environmental exposure and are discounted when the estimated amounts are reasonably fixed and determinable. If recoveries of remediation costs from third parties are probable, a receivable is recorded and is discounted when the estimated amount is reasonably fixed and determinable.
Asset retirement obligations	Asset Retirement Obligations – An ARO is a legal obligation associated with the retirement of tangible long-lived assets that generally result from the acquisition, construction, development or normal operation of the asset. AROs are recorded at fair value in the period in which they are incurred, if a reasonable estimate of fair value can be made, and added to the carrying amount of the associated asset. This additional carrying amount is then depreciated over the life of the asset. The liability is determined using a credit adjusted risk free interest rate and increases due to the passage of time based on the time value of money until the obligation is settled. AROs have not been recognized for certain assets because the fair value cannot be reasonably estimated since the settlement dates of the obligations are indeterminate. Such obligations will be recognized in the period when sufficient information becomes available to estimate a range of potential settlement dates. At December 31, 2021, MPLX’s asset retirement obligation was $31 million, which is included on the balance sheet within “Deferred credits and other liabilities.”
Investment in unconsolidated affiliates	Investment in Unconsolidated Affiliates – Equity investments in which MPLX exercises significant influence, but does not control and is not the primary beneficiary, are accounted for using the equity method and are reported in “Equity method investments” on the accompanying Consolidated Balance Sheets. This includes entities in which we hold majority ownership but the minority shareholders have substantive participating rights. Differences in the basis of the investments and the separate net asset values of the investees, if any, are amortized into net income over the remaining useful lives of the underlying assets and liabilities, except for the excess related to goodwill.
Derivative instruments	Derivative Instruments – MPLX may use commodity derivatives to economically hedge a portion of its exposure to commodity price risk. All derivative instruments (including derivatives embedded in other contracts) are recorded at fair value. Certain commodity derivatives are reflected on the consolidated balance sheets on a net basis by counterparty as they are governed by master netting arrangements. MPLX discloses the fair value of all derivative instruments under the captions “Other current assets” “Other noncurrent assets,” “Other current liabilities” and “Deferred credits and other liabilities” on the Consolidated Balance Sheets. Changes in the fair value of derivative instruments are reported on the Consolidated Statements of Income in accounts related to the item whose value or cash flows are being managed. All derivative instruments are marked to market through “Product sales,” “Purchased product costs,” or “Cost of revenues” on the Consolidated Statements of Income. Revenue gains and losses relate to contracts utilized to manage the cash flow for the sale of a product, typically NGLs. Purchased product costs gains and losses relate to contracts utilized to manage the cost of natural gas purchases, typically related to keep-whole arrangements. Cost of revenues gains and losses relate to a contract utilized to manage electricity costs. Changes in risk management for unrealized activities are reported as an adjustment to net income in computing cash flow from operating activities on the accompanying Consolidated Statements of Cash Flows. MPLX did not utilize any commodity derivatives during the years ended December 31, 2021, 2020 and 2019, and therefore did not elect hedge accounting. MPLX has historically elected the normal purchases and normal sales designation for certain contracts related to the physical purchase of electric power and the sale of some commodities.
Fair value measurement	Fair Value Measurement – Financial assets and liabilities recorded at fair value in the Consolidated Balance Sheets are categorized based upon the fair value hierarchy established by GAAP, which classifies the inputs used to measure fair value into Level 1, Level 2 or Level 3. A financial instrument’s categorization within the valuation hierarchy is based upon the lowest level of input that is significant to the fair value measurement. The methods and assumptions utilized may produce a fair value that may not be realized in future periods upon settlement. Furthermore, while MPLX believes its valuation methods are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different estimate of fair value at the reporting date. For further discussion, see Note 15.
Equity-based compensation arrangements	Equity-Based Compensation Arrangements – MPLX issues phantom units under the MPLX LP 2018 Incentive Compensation Plan. A phantom unit entitles the grantee a right to receive a common unit upon the issuance of the phantom unit. The fair value of phantom unit awards granted to employees and non-employee directors is based on the fair market value of MPLX LP common units on the date of grant. The fair value of the units awarded is amortized into earnings using a straight-line amortization schedule over the period of service corresponding with the vesting period. For phantom units that vest immediately and are not forfeitable, equity-based compensation expense is recognized at the time of grant. MPLX previously issued performance units under the MPLX LP 2018 Incentive Compensation Plan. Performance units paying out in cash are accounted for as liability awards and recorded at fair value with a mark-to-market adjustment made each quarter. The performance units paying out in units are accounted for as equity awards. Equity-classified performance units with a market condition use a Monte Carlo valuation model to calculate a grant date fair value of market conditions. Equity-classified performance units with a performance condition are valued based on the grant date fair value of the payout deemed most probable to occur and is adjusted as the expectation for payout changes. To satisfy common unit awards, MPLX may issue new common units, acquire common units in the open market or use common units already owned by the general partner.
Income taxes	Income Taxes – MPLX is not a taxable entity for United States federal income tax purposes or for the majority of the states that impose an income tax. Taxes on MPLX’s net income generally are borne by its partners through the allocation of taxable income. MPLX’s taxable income or loss, which may vary substantially from the net income or loss reported on the Consolidated Statements of Income, is includable in the federal income tax returns of each partner. MPLX and certain legal entities are, however, taxable entities under certain state jurisdictions. MPLX accounts for income taxes under the asset and liability method. Deferred income taxes are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax basis, capital loss carryforwards and net operating loss and credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates applied to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect of any tax rate change on deferred taxes is recognized as tax expense/(benefit) from continuing operations in the period that includes the enactment date of the tax rate change. Realizability of deferred tax assets is assessed and, if not more likely than not, a valuation allowance is recorded to reflect the deferred tax assets at net realizable value as
Incentive Distribution Policy, Managing Member or General Partner, Description	Distributions – In preparing the Consolidated Statements of Equity, net income attributable to MPLX LP is allocated to Series A and Series B preferred unitholders based on a fixed distribution schedule, as discussed in Notes 7 and 9, and subsequently allocated to the general partner and limited partner unitholders. Distributions, although earned, are not accrued as a liability until declared. The allocation of net income attributable to MPLX LP for purposes of calculating net income per limited partner unit is described below.
Net income per limited partner unit	Net Income Per Limited Partner Unit – MPLX uses the two-class method when calculating the net income per unit applicable to limited partners, because there is more than one class of participating security. The classes of participating securities include common units, Series A and Series B preferred units and certain equity-based compensation awards. Net income attributable to MPLX LP is allocated to the unitholders differently for preparation of the Consolidated Statements of Equity and the calculation of net income per limited partner unit. In preparing the Consolidated Statements of Equity, net income attributable to MPLX LP is allocated to Series A and Series B preferred unitholders based on a fixed distribution schedule and subsequently allocated to remaining unitholders in accordance with their respective ownership percentages. The allocation of net income attributable to MPLX LP for purposes of calculating net income per limited partner unit is described in Note 8. In preparing net income per limited partner units, during periods in which a net loss attributable to MPLX is reported or periods in which the total distributions exceed the reported net income attributable to MPLX’s unitholders, the amount allocable to certain equity-based compensation awards is based on actual distributions to the equity-based compensation awards. Diluted earnings per unit is calculated by dividing net income attributable to MPLX’s common unitholders, after deducting amounts allocable to other participating securities, by the weighted average number of common units and potential common units outstanding during the period. Potential common units are excluded from the calculation of diluted earnings per unit during periods in which net income attributable to MPLX’s unitholders, after deducting amounts that are allocable to the outstanding equity-based compensation awards and preferred units, is a loss, as the impact would be anti-dilutive.
Business combinations	Business Combinations – MPLX recognizes and measures the assets acquired and liabilities assumed in a business combination based on their estimated fair values at the acquisition date, with any remaining difference recorded as goodwill or gain from a bargain purchase. Depending on the nature of the transaction, management may engage an independent valuation specialist to assist with the determination of fair value of the assets acquired, liabilities assumed, noncontrolling interests, if any, and goodwill, based on recognized business valuation methodologies. If the initial accounting for the business combination is incomplete by the end of the reporting period in which the acquisition occurs, an estimate will be recorded. Subsequent to the acquisition, and not later than one year from the acquisition date, MPLX will record any material adjustments to the initial estimate based on new information obtained that would have existed as of the acquisition date. An adjustment that arises from information obtained that did not exist as of the date of the acquisition will be recorded in the period of the adjustment. An income, market or cost valuation method may be utilized to estimate the fair value of the assets acquired, liabilities assumed, and noncontrolling interests, if any, in a business combination. The income valuation method represents the present value of future cash flows over the life of the asset using: (i) discrete financial forecasts, which rely on management’s estimates of volumes, certain commodity prices, revenue and operating expenses; (ii) long-term growth rates; and (iii) appropriate discount rates. The market valuation method uses prices paid for a reasonably similar asset by other purchasers in the market, with adjustments relating to any differences between the assets. The cost valuation method is based on the replacement cost of a comparable asset at prices at the time of the acquisition reduced for depreciation of the asset. Acquisition-related costs are expensed as incurred in connection with each business combination. Acquisitions in which the company or business being acquired by MPLX had an existing relationship with MPC may result in the transaction being considered a transfer between entities under common control. In this situations, MPLX records the assets acquired and liabilities assumed on its consolidated balance sheets at MPC’s historical carrying value. For the acquiring entity, transfers of businesses between entities under common control require prior periods to be retrospectively adjusted for those dates that the entity was under common control. See Note 4 for more information about the acquisitions.

Investments and Noncontrollin_2

Investments and Noncontrolling Interests (Tables)	12 Months Ended
	Dec. 31, 2021
Equity Method Investments and Joint Ventures [Abstract]
Equity Method Investments	The following table presents MPLX’s equity method investments at the dates indicated: Ownership as of Carrying value at December 31, December 31, (In millions, except ownership percentages) 2021 2021 2020 L&S MarEn Bakken Company LLC (1) 25% $ 449 $ 465 Illinois Extension Pipeline Company, L.L.C. 35% 243 254 LOOP LLC 41% 265 252 Andeavor Logistics Rio Pipeline LLC (2) 67% 183 194 Minnesota Pipe Line Company, LLC 17% 183 188 Whistler Pipeline LLC (2) 38% 155 185 W2W Holdings LLC (2) 50% 58 72 Explorer Pipeline Company 25% 66 72 Other (2) 116 103 Total L&S 1,718 1,785 G&P MarkWest Utica EMG, L.L.C. (2) 57% 680 698 Sherwood Midstream LLC (2) 50% 544 557 MarkWest EMG Jefferson Dry Gas Gathering Company, L.L.C. (2) 67% 332 307 MarkWest Torñado GP, L.L.C. (2) 60% 246 188 Rendezvous Gas Services, L.L.C. (2) 78% 147 159 Sherwood Midstream Holdings LLC (2) 51% 136 148 Centrahoma Processing LLC 40% 133 145 Other (2) 45 49 Total G&P 2,263 2,251 Total $ 3,981 $ 4,036 (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	Summarized financial information for MPLX’s equity method investments for the years ended December 31, 2021, 2020 and 2019 is as follows: December 31, 2021 (In millions) Other VIEs Non-VIEs Total Revenues and other income $ 820 $ 1,236 $ 2,056 Costs and expenses 490 568 1,058 Income from operations 330 668 998 Net income 266 594 860 Income from equity method investments (1) $ 175 $ 146 $ 321 December 31, 2020 (In millions) Other VIEs Non-VIEs Total Revenues and other income $ 298 $ 1,208 $ 1,506 Costs and expenses 414 531 945 (Loss)/income from operations (116) 677 561 Net (loss)/income (175) 615 440 (Loss)/income from equity method investments (1) $ (1,100) $ 164 $ (936) December 31, 2019 (2) (In millions) Other VIEs Non-VIEs Total Revenues and other income $ 650 $ 1,417 $ 2,067 Costs and expenses 375 568 943 Income from operations 275 849 1,124 Net income 215 752 967 Income from equity method investments (1) $ 103 $ 187 $ 290 (1) The 2021, 2020 and 2019 amounts include impairment of $6 million, $1,264 million and $42 million, respectively. (2) The financial information for equity method investments for 2019 includes financial information of equity method investments acquired as part of the Merger. Summarized balance sheet information for MPLX’s equity method investments as of December 31, 2021 and 2020 is as follows: December 31, 2021 (In millions) Other 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 December 31, 2020 (In millions) Other VIEs Non-VIEs Total Current assets $ 530 $ 318 $ 848 Noncurrent assets 6,889 4,997 11,886 Current liabilities 323 187 510 Noncurrent liabilities $ 1,904 $ 830 $ 2,734

Related Party Agreements and _2

Related Party Agreements and Transactions (Tables)	12 Months Ended
	Dec. 31, 2021
Related Party Transaction [Line Items]
Related Party Transactions Disclosure [Text Block]	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 and 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. In addition, MPLX has obligations to MPC for services provided to MPLX by MPC under omnibus and employee services type agreements as well as other various agreements as discussed below. The commercial agreements with MPC include: • MPLX has a fuels distribution agreement with MPC under which MPC pays MPLX a tiered monthly volume-based fee for marketing and selling MPC’s products. This agreement is subject to a minimum quarterly volume and has an initial term of 10 years, subject to a five • MPLX has various pipeline transportation agreements under which MPC pays MPLX fees for transporting crude and refined products on MPLX’s pipeline systems. These agreements are subject to minimum throughput volumes under which MPC will pay MPLX deficiency payments for any period in which they do not ship the minimum committed volume. These deficiency payments can be applied as credits to future periods in which MPC ships volumes in excess of the minimum volume, subject to a limited period of time. These agreements are subject to various terms and renewal periods. • MPLX has a marine transportation agreement with an initial term of six years under which MPC pays MPLX fees for providing marine transportation of crude oil, feedstock and refined petroleum products, and related services. This agreement is subject to two automatic renewal periods of five years each. This agreement is currently in the first renewal term. • MPLX has a month-to-month trucking transportation services agreement under which MPC pays MPLX fees for gathering barrels and providing trucking, dispatch, delivery and data services. • MPLX has numerous storage services agreements governing storage services at various types of facilities including terminals, pipeline tank farms, caverns and refineries, under which MPC pays MPLX per-barrel fees for providing storage services. Some of these agreements provide MPC with exclusive access to storage at certain locations, such as storage located at MPC’s refineries or storage in certain caverns. Under these agreements, MPC pays MPLX a per-barrel fee for such storage capacity, regardless of whether MPC fully utilizes the available capacity. Many of the refinery storage agreements also contain provisions for logistical services to be provided by MPLX, for which MPC pays monthly fees. These agreements are subject to various terms and renewal periods. • MPLX has multiple terminal services agreements governing certain terminals under which MPC pays MPLX fees for terminal services for refined petroleum products. Under these agreements MPC pays MPLX agreed upon fees relating to MPC product receipts, deliveries and storage as well as any blending, additization, handling, transfers or other related charges. Many of these agreements are subject to minimum volume throughput commitments, or to various minimum commitments related to some or all terminal activities, under which MPC pays a deficiency payment for any period in which they do not meet the minimum commitment. Some of these agreements allow for deficiency payments to be applied as credits to a limited number of future periods with excess throughput volumes. These agreements are subject to various terms and renewal periods. • MPLX has a year to year 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. The pricing structure under this agreement provides for a base volume subject to a base rate and incremental volumes subject to variable rates which are calculated with reference to certain of our costs incurred as processor of the volumes. The pricing for both the base and incremental volumes are subject to revision each year. In many cases, agreements are location-based hybrid agreements, containing provisions relating to multiple of the types of agreements and services described above. Operating Agreements MPLX operates various pipelines owned by MPC under operating services agreements. Under these operating services agreements, MPLX receives an operating fee for operating the assets and is reimbursed for all direct and indirect costs associated with operating the assets. Most of these agreements are indexed for inflation. These agreements range from one Co-location Services Agreements MPLX is party to co-location services agreements with MPC’s refineries, under which MPC provides management, operational and other services to the subsidiaries of MPLX Refining Logistics LLC (“Refining Logistics”). Refining Logistics pays MPC monthly fixed fees and direct reimbursements for such services calculated as set forth in the agreements. These agreements have initial terms of 50 years. Ground Lease Agreements MPLX is party to ground lease agreements with certain of MPC’s refineries under which MPLX is the lessor of certain sections of property which contain facilities owned by Refining Logistics and are within the premises of MPC’s refineries. Refining Logistics pays MPC monthly fixed fees under these ground leases. These agreements are subject to various terms. Marine Services Agreements with MPC MPLX has a management services agreement and a loss control agreement with MPC under which it provides management and loss control services to assist MPC in the oversight and management of the marine business. MPLX receives fixed annual fees for providing the required services, which are subject to predetermined annual escalation rates. These agreements are subject to initial terms of five years and automatically renew for one additional five Omnibus Agreements MPLX has omnibus agreements with MPC that address MPLX’s payment of fixed annual fees to MPC for the provision of executive management services by certain executive officers of the general partner and MPLX’s reimbursement of MPC for the provision of certain general and administrative services to it. They also provide for MPC’s indemnification to MPLX for certain matters, including environmental, title and tax matters; as well as our indemnification of MPC for certain matters under these agreements. Employee Services Agreements MPLX has various employee services agreements and secondment agreements with MPC under which MPLX reimburses MPC for employee benefit expenses, along with the provision of operational and management services in support of both our L&S and G&P segments’ operations. Loan Agreement MPLX is party to a loan agreement (the “MPC Loan Agreement”) with MPC Investment LLC (“MPC Investment”), a wholly owned subsidiary of MPC. Under the terms of the MPC Loan Agreement, MPC Investment extends loans to MPLX on a revolving basis as requested by MPLX and as agreed to by MPC Investment. The MPC Loan Agreement has a borrowing capacity of $1.5 billion in aggregate principal amount of all loans outstanding at any one time. The MPC Loan Agreement is scheduled to expire, and borrowings under the MPC 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 the maturity date. Borrowings under the MPC Loan Agreement prior to July 31, 2019 bore interest at LIBOR plus 1.50 percent, while borrowings as of and after July 31, 2019 will bear interest at the one-month 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 17. Activity on the MPC Loan Agreement was as follows: (In millions, except %) December 31, 2021 December 31, 2020 Borrowings $ 8,493 $ 6,264 Average interest rate of borrowings 1.341 % 2.278 % Repayments $ 7,043 $ 6,858 Outstanding balance at end of period $ 1,450 $ — Related Party Revenue Related party sales to MPC consist of crude oil and refined products pipeline and trucking transportation services based on tariff/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. There were additional product sales to MPC that 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 years ended December 31, 2021, 2020 and 2019, these sales totaled $811 million, $462 million and $1,120 million, respectively . Related Party Expenses MPC provides executive management services and certain general and administrative services to MPLX under the terms of our omnibus agreements. 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 rent and lease agreements with MPC. MPC has also been advancing certain strategic priorities to lay a foundation for long-term success, including plans to optimize its assets and structurally lower costs in 2021 and beyond, which included an involuntary workforce reduction plan. The workforce reduction plan, together with employee reductions resulting from MPC's indefinite idling of its Martinez, California and Gallup, New Mexico refineries, affected approximately 2,050 employees. All of the employees that conduct MPLX’s business are directly employed by affiliates of MPC, and certain of those employees were affected by MPC’s workforce reductions. During 2020, MPLX reimbursed MPC for $37 million related to severance and employee benefits related expenses that MPC recorded in connection with its workforce reductions. These costs are shown on the Consolidated Statements of Income as “Restructuring expenses.” There were no similar costs in 2021. For the years ended December 31, 2021, 2020 and 2019, “General and administrative expenses” incurred from MPC totaled $250 million, $254 million and $243 million, respectively. Some charges incurred under the omnibus and employee service 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 2021, 2020 and 2019, these charges totaled $55 million, $97 million and $169 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 (see Note 20 for additional information) 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. December 31, (In millions) 2021 2020 Current assets - related parties Receivables - MPC $ 548 $ 615 Receivables - Other 7 27 Prepaid - MPC 4 4 Other - MPC 3 1 Lease Receivables - MPC 82 30 Total 644 677 Noncurrent assets - related parties Long-term receivables - MPC 31 32 Right of use assets - MPC 229 231 Long-term lease receivables - MPC 854 386 Unguaranteed residual asset - MPC 47 23 Total 1,161 672 Current liabilities - related parties Payables - MPC (1) 1,657 215 Payables - Other 45 43 Operating lease liabilities - MPC 1 1 Deferred revenue - Minimum volume deficiencies - MPC 35 66 Deferred revenue - Project reimbursements - MPC 41 30 Deferred revenue - Project reimbursements - Other 1 1 Total 1,780 356 Long-term liabilities - related parties Long-term operating lease liabilities - MPC 228 229 Long-term deferred revenue - Project reimbursements - MPC 68 47 Long-term deferred revenue - Project reimbursements - Other 6 7 Total $ 302 $ 283 (1) Includes $1,450 million as of the year ended December 31, 2021 related to outstanding borrowings on the intercompany loan with MPC.
Schedule of Long-term Debt Instruments [Table Text Block]	Loan Agreement MPLX is party to a loan agreement (the “MPC Loan Agreement”) with MPC Investment LLC (“MPC Investment”), a wholly owned subsidiary of MPC. Under the terms of the MPC Loan Agreement, MPC Investment extends loans to MPLX on a revolving basis as requested by MPLX and as agreed to by MPC Investment. The MPC Loan Agreement has a borrowing capacity of $1.5 billion in aggregate principal amount of all loans outstanding at any one time. The MPC Loan Agreement is scheduled to expire, and borrowings under the MPC 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 the maturity date. Borrowings under the MPC Loan Agreement prior to July 31, 2019 bore interest at LIBOR plus 1.50 percent, while borrowings as of and after July 31, 2019 will bear interest at the one-month 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 17. Activity on the MPC Loan Agreement was as follows: (In millions, except %) December 31, 2021 December 31, 2020 Borrowings $ 8,493 $ 6,264 Average interest rate of borrowings 1.341 % 2.278 % Repayments $ 7,043 $ 6,858 Outstanding balance at end of period $ 1,450 $ —
Schedule of Related Party Transactions [Table Text Block]	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 (see Note 20 for additional information) 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. December 31, (In millions) 2021 2020 Current assets - related parties Receivables - MPC $ 548 $ 615 Receivables - Other 7 27 Prepaid - MPC 4 4 Other - MPC 3 1 Lease Receivables - MPC 82 30 Total 644 677 Noncurrent assets - related parties Long-term receivables - MPC 31 32 Right of use assets - MPC 229 231 Long-term lease receivables - MPC 854 386 Unguaranteed residual asset - MPC 47 23 Total 1,161 672 Current liabilities - related parties Payables - MPC (1) 1,657 215 Payables - Other 45 43 Operating lease liabilities - MPC 1 1 Deferred revenue - Minimum volume deficiencies - MPC 35 66 Deferred revenue - Project reimbursements - MPC 41 30 Deferred revenue - Project reimbursements - Other 1 1 Total 1,780 356 Long-term liabilities - related parties Long-term operating lease liabilities - MPC 228 229 Long-term deferred revenue - Project reimbursements - MPC 68 47 Long-term deferred revenue - Project reimbursements - Other 6 7 Total $ 302 $ 283 (1) Includes $1,450 million as of the year ended December 31, 2021 related to outstanding borrowings on the intercompany loan with MPC.

Equity (Tables)

Equity (Tables)	12 Months Ended
	Dec. 31, 2021
Equity [Abstract]
Schedule of Stockholders Equity	The table below summarizes the changes in the number of units outstanding for the years ended December 31, 2019, 2020, and 2021: (In units) Total Common Units Balance at December 31, 2018 794,089,518 Unit-based compensation awards 288,031 Issuance of units in connection with the Merger (See Note 4) 262,829,592 Conversion of Series A preferred units 1,148,330 Balance at December 31, 2019 1,058,355,471 Unit-based compensation awards 478,438 Wholesale Exchange (18,582,088) Units redeemed in unit repurchase program (1,473,843) Balance at December 31, 2020 1,038,777,978 Unit-based compensation awards 214,466 Conversion of Series A preferred units 93,108 Units redeemed in unit repurchase program (22,907,174) Balance at December 31, 2021 1,016,178,378
Distributions Made to Limited Partner, by Distribution	The allocation of total quarterly cash distributions to general, limited, and preferred unitholders is as follows for the years ended December 31, 2021, 2020 and 2019. 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. (In millions) 2021 2020 2019 Limited partners' distributions: Common unitholders, includes common units of general partner (1) $ 3,432 $ 2,872 $ 2,635 Series A preferred unit distributions (1) 100 81 81 Series B preferred unit distribution 41 41 42 Total cash distributions declared $ 3,573 $ 2,994 $ 2,758 (1) 2021 period includes the Special Distribution Amount.

Net Income (Loss) Per Limited_2

Net Income (Loss) Per Limited Partner Unit (Tables)	12 Months Ended
	Dec. 31, 2021
Earnings Per Share [Abstract]
Schedule of Distributions By Partner By Class [Table Text Block]	(In millions) 2021 2020 2019 Net income/(loss) attributable to MPLX LP $ 3,077 $ (720) $ 1,033 Less: Distributions declared on Series A preferred units (1) 100 81 81 Distributions declared on Series B preferred units 41 41 42 Limited partners’ distributions declared on MPLX common units (including common units of general partner) (1)(2) 3,432 2,872 2,635 Undistributed net loss attributable to MPLX LP $ (496) $ (3,714) $ (1,725) (1) The year ended December 31, 2021 includes the Special Distribution Amount. (2) Distributions on common units exclude $37.5 million of waived distributions for the year ended December 31, 2019, with respect to units held by MPC and its affiliates.
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]	2021 (In millions, except per unit data) Limited 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 $ 3,432 $ 100 $ 41 $ 3,573 Undistributed net loss attributable to MPLX LP (496) — — (496) Net income attributable to MPLX LP $ 2,936 $ 100 $ 41 $ 3,077 Weighted average units outstanding: Basic 1,027 1,027 Diluted 1,027 1,027 Net income attributable to MPLX LP per limited partner unit: Basic $ 2.86 Diluted $ 2.86 2020 (In millions, except per unit data) Limited Series A Preferred Units Series B Preferred Units Total Basic and diluted net (loss)/income attributable to MPLX LP per unit: Net (loss)/income attributable to MPLX LP: Distributions declared $ 2,872 $ 81 $ 41 $ 2,994 Undistributed net loss attributable to MPLX LP (3,714) — — (3,714) Net (loss)/income attributable to MPLX LP $ (842) $ 81 $ 41 $ (720) Weighted average units outstanding: Basic 1,051 1,051 Diluted 1,051 1,051 Net loss attributable to MPLX LP per limited partner unit: Basic $ (0.80) Diluted $ (0.80) 2019 (In millions, except per unit data) Limited 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: Distribution declared $ 2,635 $ 81 $ 42 $ 2,758 Undistributed net loss attributable to MPLX LP (1,725) — — (1,725) Net income attributable to MPLX LP $ 910 $ 81 $ 42 $ 1,033 Weighted average units outstanding: Basic 906 906 Diluted 907 907 Net income attributable to MPLX LP per limited partner unit: Basic $ 1.00 Diluted $ 1.00

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2021
Segment Reporting [Abstract]
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. (In millions) 2021 2020 2019 Reconciliation to Net income/(loss): L&S Segment Adjusted EBITDA $ 3,681 $ 3,488 $ 2,748 G&P Segment Adjusted EBITDA 1,879 1,723 1,586 Total reportable segments 5,560 5,211 4,334 Depreciation and amortization (1) (1,287) (1,377) (1,254) Provision for income taxes (1) (2) — Amortization of deferred financing costs (70) (61) (42) Gain on extinguishment of debt 10 19 — Non-cash equity-based compensation (9) (14) (22) Impairment expense (42) (2,165) (1,197) Net interest and other financial costs (819) (854) (873) Income/(loss) from equity method investments 321 (936) 290 Distributions/adjustments related to equity method investments (537) (499) (562) Unrealized derivative (losses)/gains (2) (45) (3) 1 Acquisition costs — — (14) Restructuring expenses — (37) — Other (8) (6) (1) Adjusted EBITDA attributable to noncontrolling interests 39 37 32 Adjusted EBITDA attributable to Predecessor (3) — — 770 Net income/(loss) $ 3,112 $ (687) $ 1,462 (1) Depreciation and amortization attributable to L&S was $546 million, $633 million and $503 million for the years ended 2021, 2020 and 2019, respectively. Depreciation and amortization attributable to G&P was $741 million, $744 million and $751 million for 2021, 2020 and 2019, respectively. (2) MPLX makes 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. (3) The Adjusted EBITDA adjustments related to Predecessor are excluded from Adjusted EBITDA attributable to MPLX LP prior to the acquisition date.
Reconciliation of Assets from Segment to Consolidated [Table Text Block]	December 31, (In millions) 2021 2020 Segment assets Cash and cash equivalents $ 13 $ 15 L&S 20,655 20,938 G&P 14,839 15,461 Total assets $ 35,507 $ 36,414
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 as well as total assets for our reportable segments: (In millions) 2021 2020 2019 L&S Service revenue $ 3,918 $ 3,889 $ 3,765 Rental income 772 985 1,235 Sales-type lease revenue 435 152 7 Product related revenue 14 51 91 Income from equity method investments 153 154 200 Other income 61 54 54 Total segment revenues and other income (1) 5,353 5,285 5,352 Segment Adjusted EBITDA (2) 3,681 3,488 2,748 Restructuring expenses — 29 — Capital expenditures (3) 316 498 1,060 Investments in unconsolidated affiliates 33 141 289 G&P Service revenue 2,023 2,088 2,188 Rental income 347 365 349 Product related revenue 2,066 868 997 Income/(loss) from equity method investments 168 (1,090) 90 Other income 70 53 65 Total segment revenues and other income (1) 4,674 2,284 3,689 Segment Adjusted EBITDA (2) 1,879 1,723 1,586 Restructuring expenses — 8 — Capital expenditures (3) 224 441 1,203 Investments in unconsolidated affiliates $ 118 $ 125 $ 424 (1) Within the total segment revenues and other income amounts presented above, third party revenues for the L&S segment were $503 million, $567 million and $660 million for 2021, 2020 and 2019, respectively. Third party revenues for the G&P segment were $4,463 million, $2,088 million and $3,474 million for 2021, 2020 and 2019, respectively. (2) See below for the reconciliation from Segment Adjusted EBITDA to “Net income/(loss).”

Inventories (Tables)

Inventories (Tables)	12 Months Ended
	Dec. 31, 2021
Inventory Disclosure [Abstract]
Summary of Inventories	Inventories consist of the following: December 31, (In millions) 2021 2020 NGLs $ 12 $ 5 Line fill 23 13 Spare parts, materials and supplies 107 100 Total inventories $ 142 $ 118

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2021
Property, Plant and Equipment [Abstract]
Summary of Property, Plant and Equipment	Property, plant and equipment with associated accumulated depreciation is shown below: Estimated December 31, (In millions) 2021 2020 L&S Pipelines 3-50 years $ 6,299 $ 6,026 Refining logistics 13-40 years 1,650 2,333 Terminals 4-40 years 1,655 1,643 Marine 15-20 years 965 965 Land, building and other 2-60 years 1,589 1,584 Construction-in-progress 213 262 Total L&S property, plant and equipment 12,371 12,813 G&P Gathering and transportation 5-40 years 7,668 7,547 Processing and fractionation 10-40 years 5,795 5,721 Land, building and other 3-40 years 514 507 Construction-in-progress 198 287 Total G&P property, plant and equipment 14,175 14,062 Total property, plant and equipment 26,546 26,875 Less accumulated depreciation (1) 6,504 5,657 Property, plant and equipment, net $ 20,042 $ 21,218 (1) Includes property, plant and equipment impairment charges recorded during the respective period, as discussed below.

Goodwill and Intangibles (Table

Goodwill and Intangibles (Tables)	12 Months Ended
	Dec. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	The changes in carrying amount of goodwill were as follows for the periods presented: (In millions) L&S G&P Total Gross goodwill as of December 31, 2019 $ 7,722 $ 3,141 $ 10,863 Accumulated impairment losses — (1,327) (1,327) Balance as of December 31, 2019 7,722 1,814 9,536 Impairment losses — (1,814) (1,814) Wholesale Exchange (Note 4) (65) — (65) Balance as of December 31, 2020 7,657 — 7,657 Impairment losses — — — Balance as of December 31, 2021 7,657 — 7,657 Gross goodwill as of December 31, 2021 7,657 3,141 10,798 Accumulated impairment losses — (3,141) (3,141) Balance as of December 31, 2021 $ 7,657 $ — $ 7,657
Schedule of Acquired Finite-Lived Intangible Assets by Major Class	MPLX’s intangible assets are comprised of customer contracts and relationships. Gross intangible assets with accumulated amortization as of December 31, 2021 and 2020 is shown below: December 31, 2021 December 31, 2020 (In millions) Useful Life Gross Accumulated Amortization (1) Net Gross Accumulated Amortization (1)(2) Net L&S 6 - 8 years $ 283 $ (117) $ 166 $ 283 $ (81) $ 202 G&P 6 - 25 years 1,288 (623) 665 1,288 (531) 757 $ 1,571 $ (740) $ 831 $ 1,571 $ (612) $ 959 (1) Amortization expense attributable to the G&P segment for the years ended December 31, 2021 and 2020 was $92 million and $98 million, respectively. Amortization expense attributable to the L&S segment for both years ended December 31, 2021 and 2020 was $36 million. (2) Impairment charge of $177 million is included within the G&P accumulated amortization for the year ended December 31, 2020.
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense	Estimated future amortization expense related to the intangible assets at December 31, 2021 is as follows: (In millions) 2022 $ 127 2023 127 2024 127 2025 113 2026 104 Thereafter 233 Total $ 831

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]	The following table presents the financial instruments carried at fair value on a recurring basis as of December 31, 2021 and 2020 by fair value hierarchy level. MPLX has elected to offset the fair value amounts recognized for multiple derivative contracts executed with the same counterparty. December 31, 2021 2020 (In millions) Assets Liabilities Assets Liabilities Significant unobservable inputs (Level 3) Embedded derivatives in commodity contracts $ — $ (108) $ — $ (63) Total carrying value on Consolidated Balance Sheets $ — $ (108) $ — $ (63) five
Schedule of changes in Level 3 fair value measurements [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. 2021 2020 (In millions) Embedded Derivatives in Commodity Contracts (net) Embedded Derivatives in Commodity Contracts (net) Fair value at beginning of period $ (63) $ (60) Total losses (realized and unrealized) included in earnings (1) (59) (9) Settlements 14 6 Fair value at end of period (108) (63) The amount of total losses for the period included in earnings attributable to the change in unrealized gains or losses relating to liabilities still held at end of period $ (47) $ (4) (1) Losses on derivatives embedded in commodity contracts are recorded in “Purchased product costs” on the Consolidated Statements of Income.
Fair 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: December 31, 2021 2020 (In millions) Fair Value Carrying Value Fair Value Carrying Value Outstanding debt (1) $ 20,779 $ 18,664 $ 22,951 $ 20,244 (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)	12 Months Ended
	Dec. 31, 2021
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: December 31, (In millions) 2021 2020 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 $ — $ (15) $ — $ (7) Other noncurrent assets / Deferred credits and other liabilities — (93) — (56) Total $ — $ (108) $ — $ (63) (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: (In millions) 2021 2020 2019 Purchased product costs Realized loss $ (14) $ (6) $ (6) Unrealized (loss)/gain (45) (3) 1 Purchased product cost derivative loss $ (59) $ (9) $ (5)

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2021
Extinguishment of Debt [Line Items]
Summary of Outstanding Borrowings	MPLX’s outstanding borrowings at December 31, 2021 and 2020 consisted of the following: December 31, (In millions) 2021 2020 MPLX LP: Bank revolving credit facility due July 30, 2024 $ 300 $ 175 Floating rate senior notes due September 9, 2022 — 1,000 3.500% senior notes due December 1, 2022 486 486 3.375% senior notes due March 15, 2023 500 500 4.500% senior notes due July 15, 2023 989 989 4.875% senior notes due December 1, 2024 1,149 1,149 5.250% senior notes due January 15, 2025 — 708 4.000% senior notes due February 15, 2025 500 500 4.875% senior notes due June 1, 2025 1,189 1,189 1.750% senior notes due March 1, 2026 1,500 1,500 4.125% senior notes due March 1, 2027 1,250 1,250 4.250% senior notes due December 1, 2027 732 732 4.000% senior notes due March 15, 2028 1,250 1,250 4.800% senior notes due February 15, 2029 750 750 2.650% senior notes due August 15, 2030 1,500 1,500 4.500% senior notes due April 15, 2038 1,750 1,750 5.200% senior notes due March 1, 2047 1,000 1,000 5.200% senior notes due December 1, 2047 487 487 4.700% senior notes due April 15, 2048 1,500 1,500 5.500% senior notes due February 15, 2049 1,500 1,500 4.900% senior notes due April 15, 2058 500 500 Consolidated subsidiaries: MarkWest - 4.500% - 4.875% senior notes, due 2023-2025 23 23 ANDX - 3.500% - 5.200% senior notes, due 2022-2047 45 87 Financing lease obligations (1) 9 11 Total 18,909 20,536 Unamortized debt issuance costs (102) (116) Unamortized discount/premium (236) (281) Amounts due within one year (499) (764) Total long-term debt due after one year $ 18,072 $ 19,375
Schedule of Debt Payments	The following table shows five years of scheduled debt payments, including payments on finance lease obligations: (In millions) 2022 $ 502 2023 1,502 2024 1,451 2025 1,701 2026 $ 1,501
Schedule of interest payable dates	Interest on each series of MPLX LP, MarkWest and ANDX senior notes is payable semi-annually in arrears, according to the table below. Senior Notes Interest payable semi-annually in arrears 3.500% senior notes due December 1, 2022 June 1 st and December 1 st 3.375% senior notes due March 15, 2023 March 15 th and September 15 th 4.500% senior notes due July 15, 2023 January 15 th and July 15 th 4.875% senior notes due December 1, 2024 June 1 st and December 1 st 4.000% senior notes due February 15, 2025 February 15 th and August 15 th 4.875% senior notes due June 1, 2025 June 1 st and December 1 st 1.750% senior notes due March 1, 2026 March 1 st and September 1 st 4.125% senior notes due March 1, 2027 March 1 st and September 1 st 4.250% senior notes due December 1, 2027 June 1 st and December 1 st 4.000% senior notes due March 15, 2028 March 15 th and September 15 th 4.800% senior notes due February 15, 2029 February 15 th and August 15 th 2.650% senior notes due August 15, 2030 February 15 th and August 15 th 4.500% senior notes due April 15, 2038 April 15 th and October 15 th 5.200% senior notes due March 1, 2047 March 1 st and September 1 st 5.200% senior notes due December 1, 2047 June 1 st and December 1 st 4.700% senior notes due April 15, 2048 April 15 th and October 15 th 5.500% senior notes due February 15, 2049 February 15 th and August 15 th 4.900% senior notes due April 15, 2058 April 15 th and October 15 th

Revenue Revenue (Tables)

Revenue Revenue (Tables)	12 Months Ended
	Dec. 31, 2021
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 years ended December 31, 2021, 2020 and 2019: 2021 (In millions) L&S G&P Total Revenues and other income: Service revenue $ 310 $ 2,003 $ 2,313 Service revenue - related parties 3,608 20 3,628 Service revenue - product related — 345 345 Product sales 4 1,586 1,590 Product sales - related parties 10 135 145 Total revenues from contracts with customers $ 3,932 $ 4,089 8,021 Non-ASC 606 revenue (1) 2,006 Total revenues and other income $ 10,027 2020 (In millions) L&S G&P Total Revenues and other income: Service revenue $ 333 $ 2,064 $ 2,397 Service revenue - related parties 3,556 24 3,580 Service revenue - product related — 155 155 Product sales 39 597 636 Product sales - related parties 12 116 128 Total revenues from contracts with customers $ 3,940 $ 2,956 6,896 Non-ASC 606 revenue (1) 673 Total revenues and other income $ 7,569 2019 (In millions) L&S G&P Total Revenues and other income: Service revenue $ 346 $ 2,152 $ 2,498 Service revenue - related parties 3,419 36 3,455 Service revenue - product related — 140 140 Product sales 65 741 806 Product sales - related parties 26 116 142 Total revenues from contracts with customers $ 3,856 $ 3,185 7,041 Non-ASC 606 revenue (1) 2,000 Total revenues and other income $ 9,041
Contract with Customer, Contract Asset, Contract Liability, and Receivable [Table Text Block]	The tables below reflect the changes in our contract balances for the years ended December 31, 2021 and 2020: (In millions) Balance at December 31, 2020 (1) Additions/ (Deletions) Revenue Recognized (2) Balance at December 31, 2021 (1) Contract assets $ 40 $ (15) $ — $ 25 Long-term contract assets 2 — — 2 Deferred revenue 37 56 (37) 56 Deferred revenue - related parties 91 75 (106) 60 Long-term deferred revenue 119 16 — 135 Long-term deferred revenue - related parties 48 (17) — 31 Long-term contract liabilities $ 6 $ (1) $ — $ 5 (In millions) Balance at December 31, 2019 (1) Additions/ (Deletions) Revenue Recognized (2) Balance at December 31, 2020 (1) Contract assets $ 39 $ 3 $ (2) $ 40 Long-term contract assets — 2 — 2 Deferred revenue 23 22 (8) 37 Deferred revenue - related parties 53 121 (83) 91 Long-term deferred revenue 90 29 — 119 Long-term deferred revenue - related parties 55 (7) — 48 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]	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 December 31, 2021, the amounts allocated to contract assets and contract liabilities on the Consolidated Balance Sheets are $281 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 $ 1,850 2023 1,725 2024 1,592 2025 1,507 2026 and thereafter 3,283 Total revenue on remaining performance obligations (1)(2)(3) $ 9,957 (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, see further discussion about leases in Note 20. (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)	12 Months Ended
	Dec. 31, 2021
Supplemental Cash Flow Information [Abstract]
Summary of Supplemental Cash Flow Information	(In millions) 2021 2020 2019 Net cash provided by operating activities included: Interest paid (net of amounts capitalized) $ 812 $ 821 $ 835 Income taxes paid 4 2 1 Cash paid for amounts included in the measurement of lease liabilities Payments on operating leases 79 87 85 Interest payment under finance lease obligations — 1 1 Net cash provided by financing activities included: Principal payments under finance lease obligations 2 9 5 Non-cash investing and financing activities: Net transfers of property, plant and equipment from materials and supplies inventories 1 — 2 MPLX terminal lease classification change — — 21 ROU assets obtained in exchange for new operating lease obligations 20 17 26 ROU assets obtained in exchange for new finance lease obligations — 1 4 Fair value of common units redeemed for Wholesale Exchange — 340 — Contribution - common units issued (1) $ — $ — $ 7,722 (1)
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 did not affect cash. The following is the change of additions to property, plant and equipment related to capital accruals: (In millions) 2021 2020 2019 (Decrease)/increase in capital accruals $ 11 $ (244) $ (146)

Leases Lessee Disclosure (Table

Leases Lessee Disclosure (Tables)	12 Months Ended
	Dec. 31, 2021
Lessee, Lease, Description [Line Items]
Lease, Cost [Table Text Block]	The components of lease cost were as follows: 2021 2020 2019 (In millions) Related Party Third Related Third Related Third Components of lease costs: Operating lease costs $ 15 $ 71 $ 14 $ 78 $ 14 $ 75 Finance lease cost: Amortization of ROU assets — 2 — 3 — 5 Interest on lease liabilities — 1 — 1 — 1 Total finance lease cost — 3 — 4 — 6 Variable lease cost — 15 1 10 1 11 Short-term lease cost — 31 — 52 — 80 Total lease cost $ 15 $ 120 $ 15 $ 144 $ 15 $ 172
Supplemental Balance Sheet Disclosures [Text Block]	Supplemental balance sheet data related to leases were as follows: December 31, 2021 December 31, 2020 (In millions, except % and years) Related Party Third Party Related Party Third Party Operating leases Assets Right of use assets $ 229 $ 268 $ 231 $ 309 Liabilities Operating lease liabilities 1 59 1 63 Long-term operating lease liabilities 228 205 229 244 Total operating lease liabilities $ 229 $ 264 $ 230 $ 307 Weighted average remaining lease term 45.2 years 8.3 years 46.2 years 8.0 years Weighted average discount rate 5.8 % 4.1 % 5.8 % 4.3 % Finance leases Assets Property, plant and equipment, gross $ 11 $ 17 Less: Accumulated depreciation 4 8 Property, plant and equipment, net 7 9 Liabilities Long-term debt due within one year 2 2 Long-term debt 7 9 Total finance lease liabilities $ 9 $ 11 Weighted average remaining lease term 19.4 years 16.9 years Weighted average discount rate 6.0 % 6.0 %
Schedule of Future Minimum Lease Payments for Operating and Finance Leases [Table Text Block]	As of December 31, 2021, maturities of lease liabilities for operating lease obligations and finance lease obligations having initial or remaining non-cancellable lease terms in excess of one year are as follows: (In millions) Related Party Operating Third Party Operating Finance 2022 $ 15 $ 68 $ 2 2023 15 59 2 2024 14 38 1 2025 14 21 1 2026 14 18 1 2027 and thereafter 575 109 8 Gross lease payments 647 313 15 Less: Imputed interest 418 49 6 Total lease liabilities $ 229 $ 264 $ 9
Operating Lease, Lease Income	Lease revenues included on the Consolidated Statements of Income during 2021, 2020 and 2019 were as follows: 2021 2020 2019 (In millions) Related Party Third Related Party Third Related Party Third Operating leases: Rental income $ 743 $ 376 $ 952 $ 398 $ 1,196 $ 388 Sales-type leases: Profit/(loss) recognized at the commencement date — — — — — — Interest income (Sales-type rental revenue- fixed minimum) 431 — 151 — 6 — Interest income (Revenue from variable lease payments) 4 — 1 — 1 — Sales-type lease revenue $ 435 $ — $ 152 $ — $ 7 $ —
Sales-type Lease, Lease Income [Table Text Block]	Lease revenues included on the Consolidated Statements of Income during 2021, 2020 and 2019 were as follows: 2021 2020 2019 (In millions) Related Party Third Related Party Third Related Party Third Operating leases: Rental income $ 743 $ 376 $ 952 $ 398 $ 1,196 $ 388 Sales-type leases: Profit/(loss) recognized at the commencement date — — — — — — Interest income (Sales-type rental revenue- fixed minimum) 431 — 151 — 6 — Interest income (Revenue from variable lease payments) 4 — 1 — 1 — Sales-type lease revenue $ 435 $ — $ 152 $ — $ 7 $ —
Lessor, Operating Lease, Payment to be Received, Fiscal Year Maturity [Table Text Block]	The following is a schedule of minimum future rental revenue on the non-cancellable operating leases as of December 31, 2021: (In millions) Related Party Third Party Total 2022 $ 632 $ 213 $ 845 2023 563 207 770 2024 514 204 718 2025 511 171 682 2026 504 142 646 2027 and thereafter 308 1,299 1,607 Total minimum future rentals $ 3,032 $ 2,236 $ 5,268
Sales-type and Direct Financing Leases, Lease Receivable, Maturity [Table Text Block]	The following is a schedule of minimum future revenue on sales-type leases as of December 31, 2021: (In millions) Related Party 2022 $ 544 2023 544 2024 538 2025 525 2026 422 2027 and thereafter 595 Total minimum future rentals 3,168 Less: present value discount 2,232 Lease receivable $ 936
Assets Held Under Operating Lease	The following schedule summarizes MPLX’s investment in assets held under operating lease by major classes as of December 31, 2021 and 2020: December 31, (In millions) 2021 2020 Pipelines $ 953 $ 834 Refining logistics 1,146 1,680 Terminals 1,290 1,276 Marine 129 129 Gathering and transportation 991 990 Processing and fractionation 867 867 Land, building and other 176 171 Total property, plant and equipment 5,552 5,947 Less: accumulated depreciation 2,042 2,007 Property, plant and equipment, net $ 3,510 $ 3,940

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Contractual Obligation, Fiscal Year Maturity Schedule	MPLX executed various third party transportation and terminalling agreements that obligate us to minimum volume, throughput or payment commitments over the remaining terms of the agreements, which range from one (In millions) 2022 $ 117 2023 155 2024 146 2025 124 2026 111 2027 and thereafter 310 Total $ 963

Description of Business and B_3

Description of Business and Basis of Presentation (Details)	Jul. 31, 2020shares	Jul. 30, 2019shares	Oct. 31, 2012	Mar. 27, 2012	Dec. 31, 2021
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Date of partnership formation				Mar. 27, 2012
Date for initial public offering completed			Oct. 31, 2012
Number of reportable segments					2
Western Refining Wholesale & Western Refining Product Transport [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Partners' Capital Account, Units, Redeemed	18,582,088
Public | ANDX LP [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Common Units Conversion Ratio - ANDX to MPLX		1.135
Nonpublic [Member] | ANDX LP [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Common Units Conversion Ratio - ANDX to MPLX		1.0328

Summary of Principal Accounti_3

Summary of Principal Accounting Policies (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Accounting Policies [Abstract]
Asset Retirement Obligation	$ 31
Restricted Cash	$ 0	$ 0

Javelina Disposition (Details)

Javelina Disposition (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)
Sale of Javelina Assets and Liabilities
Business Acquisition [Line Items]
Gain (Loss) on Disposition of Assets	$ 0

Wholesale Exchange (Details)

Wholesale Exchange (Details) - USD ($) $ in Millions	Jul. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Goodwill		$ 7,657	$ 7,657	$ 9,536
Western Refining Wholesale & Western Refining Product Transport [Member]
Business Acquisition [Line Items]
Partners' Capital Account, Units, Redeemed	18,582,088
Partner Capital, Units, contributed, fair value assigned	$ 340
Fair Value, Net Asset (Liability)	90
Excess of Fair Value over Book Value	250
Goodwill	$ 65

Acquisition of Andeavor Logisti

Acquisition of Andeavor Logistics LP (Details) - USD ($) $ in Millions	Jul. 30, 2019	Dec. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Jul. 31, 2020
Business Acquisition [Line Items]
Goodwill		$ 9,536	$ 7,657	$ 7,657
Andeavor Logistics [Member]
Business Acquisition [Line Items]
Acquisition Costs, Period Cost		14
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual		2,400
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual		266
ANDX LP [Member] | Public
Business Acquisition [Line Items]
Common Units Conversion Ratio - ANDX to MPLX	1.135
ANDX LP [Member] | Nonpublic [Member]
Business Acquisition [Line Items]
Common Units Conversion Ratio - ANDX to MPLX	1.0328
Western Refining Wholesale & Western Refining Product Transport [Member]
Business Acquisition [Line Items]
Goodwill					$ 65
Pro Forma [Member] | Andeavor Logistics [Member]
Business Acquisition [Line Items]
Business Acquisition, Pro Forma Net Income (Loss)		$ 1,434

Investments and Noncontrollin_3

Investments and Noncontrolling Interest (Equity Method Investments) (Details) - USD ($) $ in Millions		Dec. 31, 2021	Dec. 31, 2020
Schedule of Equity Method Investments [Line Items]
Equity Method Investments		$ 3,981	$ 4,036
Sherwood Midstream Holdings | Indirect Ownership Interest
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		24.55%
Logistics and Storage [Member] | MarEn Bakken
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	[1]	25.00%
Equity Method Investments	[1]	$ 449	465
Logistics and Storage [Member] | Illinois Extension
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		35.00%
Equity Method Investments		$ 243	254
Logistics and Storage [Member] | LOOP
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		41.00%
Equity Method Investments		$ 265	252
Logistics and Storage [Member] | Andeavor Logistics Rio Pipeline [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	[2]	67.00%
Equity Method Investments	[2]	$ 183	194
Logistics and Storage [Member] | Minnesota Pipe Line Company, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		17.00%
Equity Method Investments		$ 183	188
Logistics and Storage [Member] | Whistler Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	[2]	38.00%
Equity Method Investments	[2]	$ 155	185
Logistics and Storage [Member] | W2W Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	[2]	50.00%
Equity Method Investments	[2]	$ 58	72
Logistics and Storage [Member] | Explorer
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		25.00%
Equity Method Investments		$ 66	72
Logistics and Storage [Member] | Other VIEs and Non-VIEs [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	[2]	$ 116	103
Logistics and Storage [Member] | Bakken Pipeline System | Indirect Ownership Interest
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		9.19%
Gathering and Processing [Member] | MarkWest Utica EMG
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	[2]	57.00%
Equity Method Investments	[2]	$ 680	698
Gathering and Processing [Member] | Sherwood Midstream LLC
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	[2]	50.00%
Equity Method Investments	[2]	$ 544	557
Gathering and Processing [Member] | MarkWest EMG Jefferson Dry Gas Gathering Company, L.L.C. [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	[2]	67.00%
Equity Method Investments	[2]	$ 332	307
Gathering and Processing [Member] | MarkWest Tornado GP, L.L.C.
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	[2]	60.00%
Equity Method Investments	[2]	$ 246	188
Gathering and Processing [Member] | Rendezvous Gas Services, L.L.C. [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	[2]	78.00%
Equity Method Investments	[2]	$ 147	159
Gathering and Processing [Member] | Sherwood Midstream Holdings
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	[2]	$ 136	148
Gathering and Processing [Member] | Sherwood Midstream Holdings | Direct Ownership Interest
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	[2]	51.00%
Gathering and Processing [Member] | Centrahoma Processing LLC
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		40.00%
Equity Method Investments		$ 133	145
Gathering and Processing [Member] | Other VIEs and Non-VIEs [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	[2]	45	49
Operating Segments | Logistics and Storage [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments		1,718	1,785
Operating Segments | Gathering and Processing [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments		$ 2,263	$ 2,251
[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.

Investments and Noncontrollin_4

Investments and Noncontrolling Interests (Summary of Equity Method Investment Financial Information) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Revenues		$ 10,027	$ 7,569	$ 9,041
Total costs and expenses		6,035	7,358	6,664
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		3,112	(687)	1,462
Income (Loss) from Equity Method Investments		321	(936)	290
Income (Loss) from Equity Method Investments from Asset Impairment and Elimination of Basis Differential				42
Assets, Current		1,507	1,515
Liabilities, Current		3,348	2,086
Equity Method Investment, Other than Temporary Impairment				14
Income (Loss) from Equity Method Investments from Asset Impairment				28
MarkWest Utica EMG
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Other than Temporary Impairment			1,251
Other VIEs and Non-VIEs [Member]
Schedule of Equity Method Investments [Line Items]
Revenues		2,056	1,506	2,067	[1]
Total costs and expenses		1,058	945	943	[1]
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest		998	561	1,124	[1]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		860	440	967	[1]
Income (Loss) from Equity Method Investments	[2]	321	(936)	290	[1]
Assets, Current		746	848
Assets, Noncurrent		12,334	11,886
Liabilities, Current		527	510
Liabilities, Noncurrent		3,249	2,734
Equity Method Investment, Other than Temporary Impairment			1,264
Income (Loss) from Equity Method Investments from Asset Impairment		6
Non-VIEs
Schedule of Equity Method Investments [Line Items]
Revenues		1,236	1,208	1,417	[1]
Total costs and expenses		568	531	568	[1]
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest		668	677	849	[1]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		594	615	752	[1]
Income (Loss) from Equity Method Investments	[2]	146	164	187	[1]
Assets, Current		411	318
Assets, Noncurrent		4,895	4,997
Liabilities, Current		310	187
Liabilities, Noncurrent		788	830
Other VIEs
Schedule of Equity Method Investments [Line Items]
Revenues		820	298	650	[1]
Total costs and expenses		490	414	375	[1]
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest		330	(116)	275	[1]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		266	(175)	215	[1]
Income (Loss) from Equity Method Investments	[2]	175	(1,100)	$ 103	[1]
Assets, Current		335	530
Assets, Noncurrent		7,439	6,889
Liabilities, Current		217	323
Liabilities, Noncurrent		$ 2,461	$ 1,904
[1]	The financial information for equity method investments for 2019 includes financial information of equity method investments acquired as part of the Merger.
[2]	The 2021, 2020 and 2019 amounts include impairment of $6 million, $1,264 million and $42 million, respectively.

Investments and Noncontrollin_5

Investments and Noncontrolling Interests (Narrative) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Income (Loss) from Equity Method Investments from Asset Impairment				$ 28
Equity Method Investment, Other than Temporary Impairment				14
Income (Loss) from Equity Method Investments from Asset Impairment and Elimination of Basis Differential				$ 42
Other VIEs and Non-VIEs [Member]
Schedule of Equity Method Investments [Line Items]
Income (Loss) from Equity Method Investments from Asset Impairment		$ 6
Equity Method Investment, Other than Temporary Impairment			$ 1,264
MarkWest Utica EMG
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Other than Temporary Impairment			1,251
Sherwood Midstream Holdings | Indirect Ownership Interest
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		24.55%
Gathering and Processing [Member]
Schedule of Equity Method Investments [Line Items]
Basis difference		$ (54)	(57)
Basis difference, not amortized		$ 31	31
Gathering and Processing [Member] | MarkWest Utica EMG
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	[1]	57.00%
Gathering and Processing [Member] | Sherwood Midstream LLC
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	[1]	50.00%
Logistics and Storage [Member]
Schedule of Equity Method Investments [Line Items]
Basis difference		$ 327	331
Basis difference, not amortized		$ 167	$ 167
[1]	Investments deemed to be VIEs. Some investments included within “Other” have also been deemed to be VIEs.

Related Party Agreements and _3

Related Party Agreements and Transactions (Narrative) (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Commercial Agreements
Restructuring Charges	$ 0	$ 37	$ 0
Marathon Petroleum Corporation [Member]
Commercial Agreements
Restructuring Charges	$ 0	$ 37
Marathon Petroleum Corporation [Member] | Fuels Distribution [Member]
Commercial Agreements
Renewal Term Agreement	5 years
Term Of Agreements	10 years
Marathon Petroleum Corporation [Member] | Marine Services Equipment [Member]
Commercial Agreements
Term Of Agreements	6 years
Automatic renewal term agreement	5 years
Number of renewals	2
Commercial Agreements | Marathon Petroleum Corporation [Member] | Co-location Agreements [Member]
Commercial Agreements
Term Of Agreements	50 years
Commercial Agreements | Marathon Petroleum Corporation [Member] | Marine Management Services [Member]
Commercial Agreements
Term Of Agreements	5 years
Automatic renewal term agreement	5 years
Number of renewals	1
Operating Agreements [Member] | Marathon Petroleum Corporation [Member] | Minimum
Commercial Agreements
Term Of Agreements	1 year
Operating Agreements [Member] | Marathon Petroleum Corporation [Member] | Maximum
Commercial Agreements
Term Of Agreements	5 years

Related Party Agreements and _4

Related Party Agreements and Transactions (Intercompany Loans with Related Parties) (Detail) - MPC Investment - Related Party Revolving Credit Agreement - USD ($) $ in Millions	7 Months Ended	12 Months Ended		29 Months Ended
	Jul. 30, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2021
Related Party Transaction [Line Items]
Line of Credit Facility, Current Borrowing Capacity		$ 1,500		$ 1,500
Debt Instrument, Description of Variable Rate Basis	LIBOR plus 1.50 percent			LIBOR plus 1.25 percent
Proceeds from lines of credit		$ 8,493	$ 6,264
Interest rate during period		1.341%	2.278%
Repayments of lines of credit		$ 7,043	$ 6,858
Outstanding balance		$ 1,450	$ 0	$ 1,450

Related Party Agreements and _5

Related Party Agreements and Transactions (Summary of Revenue by Income Statement RP Line Item) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Marathon Petroleum Corporation [Member]
Related Party Transaction [Line Items]
Sales Revenue, Goods, Related Party, Net Zero	$ 811	$ 462	$ 1,120

Related Party Agreements and _6

Related Party Agreements and Transactions (Summary of Expenses by Income Statement RP Line Item) (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)employees	Dec. 31, 2019USD ($)
Related Party Transaction [Line Items]
Restructuring Charges	$ 0	$ 37	$ 0
Entity Number of Employees | employees		2,050
Marathon Petroleum Corporation [Member]
Related Party Transaction [Line Items]
Labor and Related Expense		$ 254
Restructuring Charges	0	37
Marathon Petroleum Corporation [Member] | General and Administrative Expense - Related Party [Member]
Related Party Transaction [Line Items]
Labor and Related Expense	250		243
Construction-in-progress | Marathon Petroleum Corporation [Member]
Related Party Transaction [Line Items]
Property, Plant and Equipment, Additions	$ 55	$ 97	$ 169

Related Party Agreements and _7

Related Party Agreements and Transactions (Summary of Balance Sheet by RP Line Item) (Details) - USD ($) $ in Millions	Dec. 31, 2021		Jun. 30, 2021	Dec. 31, 2020	Mar. 31, 2020
Related Party Transaction [Line Items]
Due from Related Parties, Noncurrent	$ 1,161			$ 672
Sales-type Lease, Unguaranteed Residual Asset			$ 14		$ 10
Due to Related Parties, Current	1,780			356
Due from Related Parties, Current	644			677
Due to Related Parties, Noncurrent	302			283
Other Affiliates [Member]
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties, Current	7			27
Accounts Payable, Related Parties, Current	45			43
Other Affiliates [Member] | Other current liabilities
Related Party Transaction [Line Items]
Deferred revenue related parties	1			1
Other Affiliates [Member] | Other Noncurrent Liabilities [Member]
Related Party Transaction [Line Items]
Deferred Revenue, Noncurrent, Related Parties	6			7
Marathon Petroleum Corporation [Member]
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties, Current	548			615
Prepaid Expense, Current	4			4
Other Assets, Current	3			1
Net Investment in Lease, Current	82			30
Accounts Payable, Related Parties, Current	1,657	[1]		215
Operating Lease, Right-of-Use Asset	229			231
Net Investment in Lease, Noncurrent	854			386
Sales-type Lease, Unguaranteed Residual Asset	47			23
Operating Lease, Liability, Current	1			1
Operating Lease, Liability, Noncurrent, Related Party	228			229
Accounts Receivable, Related Parties, Noncurrent	31			32
Marathon Petroleum Corporation [Member] | Minimum Committed Volume Contracts [Member]
Related Party Transaction [Line Items]
Deferred revenue related parties	35			66
Marathon Petroleum Corporation [Member] | Reimbursable Projects
Related Party Transaction [Line Items]
Deferred revenue related parties	41			30
Deferred Revenue, Noncurrent, Related Parties	$ 68			$ 47
[1]	Includes $1,450 million as of the year ended December 31, 2021 related to outstanding borrowings on the intercompany loan with MPC.

Repurchase Program (Details)

Repurchase Program (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Nov. 02, 2020
Equity, Class of Treasury Stock [Line Items]
Partners' Capital Account, Units	22,907,174	1,473,843
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 337
Stock Repurchased and Retired During Period, Value	$ 630	$ 33
Stock Repurchase Program, Authorized Amount			$ 1,000
Treasury Stock Acquired, Average Cost Per Share	$ 27.52	$ 22.29

Equity (Changes in Partners Cap

Equity (Changes in Partners Capital, Unit Rollforward) (Details) - USD ($) $ / shares in Units, $ in Millions	Jul. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2021
Stockholders Equity [Line Items]
Stock Repurchased and Retired During Period, Shares		(22,907,174)	(1,473,843)
Stock Repurchased and Retired During Period, Value		$ 630	$ 33
Treasury Stock Acquired, Average Cost Per Share		$ 27.52	$ 22.29
Western Refining Wholesale & Western Refining Product Transport [Member]
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Redeemed	(18,582,088)
Limited Partners Common Units
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Beginning Balance		1,038,777,978	1,058,355,471	794,089,518	794,089,518
Unit-based compensation awards, in units		214,466	478,438	288,031
Unit conversion		93,108		1,148,330
Partners' Capital Account, Units, Redeemed			18,582,088
Partners' Capital Account, Units, Ending Balance		1,016,178,378	1,038,777,978	1,058,355,471	1,016,178,378
Stock Repurchased and Retired During Period, Shares		(22,907,174)	(1,473,843)
Limited Partners Common Units | Marathon Petroleum Corporation [Member]
Stockholders Equity [Line Items]
Units outstanding		647,415,452	647,000,000		647,415,452
Stock Repurchased and Retired During Period, Value		$ 0	$ 0
Limited Partners Common Units | Refining Logistics & Fuels Distribution [Member]
Stockholders Equity [Line Items]
Units, acquisitions				262,829,592

Equity (Cash Distributions) (De

Equity (Cash Distributions) (Details) - USD ($) $ / shares in Units, $ in Millions	Feb. 15, 2022	Feb. 14, 2022	Feb. 04, 2022	Jan. 25, 2022	Oct. 26, 2021	Dec. 31, 2019	Dec. 31, 2021		Dec. 31, 2020	Dec. 31, 2019
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared							$ 3,573		$ 2,994	$ 2,758
Special Distribution
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution Made to Limited Partner, Distributions Declared, Per Unit					$ 0.575
Marathon Petroleum Corporation [Member] | ANDX LP [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Contribution from MPC						$ 37.5
Limited Partners Common Units
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared							3,432	[1]	2,872	2,635
Preferred Class B [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared							41		41	42
Preferred Class A [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared							100	[1]	81	81
Subsequent Event
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution made to limited partner, declaration date				Jan. 25, 2022
Distribution Made to Limited Partner, Cash Distributions Declared				$ 715
Distribution Made to Limited Partner, Distributions Declared, Per Unit				$ 0.7050
Distribution made to limited partner, date of record			Feb. 4, 2022
Subsequent Event | Limited Partners Common Units
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution made to limited partner, distribution date		Feb. 14, 2022
Subsequent Event | Preferred Class B [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared	$ 21
Limited Partners Common Units
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared							$ 3,432	[2]	$ 2,872	$ 2,635	[3]
Distribution Made to Limited Partner, Distributions Declared, Per Unit							$ 3.36	[1]	$ 2.75	$ 2.69
Preferred Partner [Member] | Preferred Class B [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders										$ (21)
[1]	2021 period includes the Special Distribution Amount.
[2]	The year ended December 31, 2021 includes the Special Distribution Amount.
[3]	Distributions on common units exclude $37.5 million of waived distributions for the year ended December 31, 2019, with respect to units held by MPC and its affiliates.

Wholesale Exchange and Merger (

Wholesale Exchange and Merger (Details) - shares	Jul. 31, 2020	Jul. 30, 2019	Dec. 31, 2020	Dec. 31, 2021
Limited Partners Common Units
Partners' Capital Account, Units, Redeemed			(18,582,088)
Limited Partners Common Units | Marathon Petroleum Corporation [Member]
Limited Partners' Capital Account, Units Issued		161,000,000	647,000,000	647,000,000
Public | Limited Partners Common Units
Limited Partners' Capital Account, Units Issued		102,000,000	391,000,000	369,000,000
Western Refining Wholesale & Western Refining Product Transport [Member]
Partners' Capital Account, Units, Redeemed	18,582,088
ANDX LP [Member] | Public
Common Units Conversion Ratio - ANDX to MPLX		1.135
ANDX LP [Member] | Nonpublic [Member]
Common Units Conversion Ratio - ANDX to MPLX		1.0328

Series A Preferred Units (Detai

Series A Preferred Units (Details) shares in Thousands	36 Months Ended
	Dec. 31, 2021shares
Series A Preferred Stock [Member]
Partners' Capital Account, Units, Converted	1,200

Series B Preferred Units (Detai

Series B Preferred Units (Details) - $ / shares	Jul. 29, 2019	Dec. 31, 2021
Series B Preferred Stock [Member]
Preferred Stock, Redemption Price Per Share		$ 1,000
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. MPLX will pay unitholders the Series B preferred unit redemption price of $1,000 per unit plus any accumulated and unpaid distributions up to the redemption date.
ANDX LP [Member]
Preferred Units, Outstanding	600,000
Preferred Stock, Dividend Rate, Percentage	6.875%
Units issued, price per unit	$ 1,000
MPLX LP [Member] | Series B Preferred Stock [Member]
Preferred Units, Outstanding		600,000
Preferred Stock, Dividend Rate, Percentage		465.20%
Preferred Stock, Dividend Payment Rate, Variable		LIBOR plus

Net Income (Loss) Per Limited_3

Net Income (Loss) Per Limited Partner Unit (Schedule of Distributions by Partner Class) (Detail) - USD ($) shares in Millions, $ in Millions	9 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2021		Dec. 31, 2020	Dec. 31, 2019
Net Income Per Share [Line Items]
Potentially dilutive securities		1		1	1
Net income/(loss) attributable to MPLX LP		$ 3,077		$ (720)	$ 1,033
Total cash distributions declared		3,573		2,994	2,758
Undistributed net loss attributable to MPLX LP		(496)		(3,714)	(1,725)
ANDX LP [Member] | Marathon Petroleum Corporation [Member]
Net Income Per Share [Line Items]
Contribution from MPC	$ 37.5
Limited Partners Common Units
Net Income Per Share [Line Items]
Total cash distributions declared		3,432	[1]	2,872	2,635	[2]
Series A Preferred Stock [Member] | Preferred Partner [Member]
Net Income Per Share [Line Items]
Net income/(loss) attributable to MPLX LP		100		81	81
Total cash distributions declared		100	[1]	81	81
Series B Preferred Stock [Member] | Preferred Partner [Member]
Net Income Per Share [Line Items]
Net income/(loss) attributable to MPLX LP		41		41	42
Total cash distributions declared		$ 41		$ 41	$ 42
[1]	The year ended December 31, 2021 includes the Special Distribution Amount.
[2]	Distributions on common units exclude $37.5 million of waived distributions for the year ended December 31, 2019, with respect to units held by MPC and its affiliates.

Net Income (Loss) Per Limited_4

Net Income (Loss) Per Limited Partner Unit (Basic and Diluted Earnings Per Unit) (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2021		Dec. 31, 2020	Dec. 31, 2019
Net income attributable to MPLX LP:
Total cash distributions declared	$ 3,573		$ 2,994	$ 2,758
Undistributed net income loss attributable to MPLX LP	(496)		(3,714)	(1,725)
Net income/(loss) attributable to MPLX LP	$ 3,077		$ (720)	$ 1,033
Weighted average units outstanding:
Basic (shares)	1,027		1,051	906
Diluted (shares)	1,027		1,051	907
Limited Partners Common Units
Net income attributable to MPLX LP:
Total cash distributions declared	$ 3,432	[1]	$ 2,872	$ 2,635	[2]
Undistributed net income loss attributable to MPLX LP	$ (496)		$ (3,714)	$ (1,725)
Weighted average units outstanding:
Basic (shares)	1,027		1,051	906
Diluted (shares)	1,027		1,051	907
Net income attributable to MPLX LP subsequent to initial public offering per limited partner unit:
Basic (in USD per unit)	$ 2.86		$ (0.80)	$ 1
Diluted (in USD per unit)	$ 2.86		$ (0.80)	$ 1
Series A Preferred Stock [Member] | Preferred Partner [Member]
Net income attributable to MPLX LP:
Total cash distributions declared	$ 100	[1]	$ 81	$ 81
Undistributed net income loss attributable to MPLX LP	0		0	0
Net income/(loss) attributable to MPLX LP	100		81	81
Series B Preferred Stock [Member] | Preferred Partner [Member]
Net income attributable to MPLX LP:
Total cash distributions declared	41		41	42
Undistributed net income loss attributable to MPLX LP	0		0	0
Net income/(loss) attributable to MPLX LP	41		41	42
Common Stock | Limited Partners Common Units
Net income attributable to MPLX LP:
Net income/(loss) attributable to MPLX LP	$ 2,936		$ (842)	$ 910
[1]	The year ended December 31, 2021 includes the Special Distribution Amount.
[2]	Distributions on common units exclude $37.5 million of waived distributions for the year ended December 31, 2019, with respect to units held by MPC and its affiliates.

Redeemable Preferred Units (Nar

Redeemable Preferred Units (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	Jan. 25, 2022	May 13, 2016	Dec. 31, 2021		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Limited Partners Common Units
Redeemable Noncontrolling Interest [Line Items]
Distribution Made to Limited Partner, Distributions Declared, Per Unit			$ 3.36	[1]	$ 2.75	$ 2.69
Partners' Capital Account, Units, Converted			93,108			1,148,330
Partners' Capital Account, Units			1,016,178,378		1,038,777,978	1,058,355,471	794,089,518
Series A Preferred Stock [Member] | Preferred Partner [Member]
Redeemable Noncontrolling Interest [Line Items]
Issuance of preferred units		30,800,000
Preferred Stock, Dividend Rate, Percentage		6.50%
Units issued, price per unit		$ 32.50
Issuance of redeemable preferred units		$ 984
Preferred units, dividend rate, per-dollar-amount		$ 0.528125
Preferred units, description		The holders may convert their Series A preferred units into common units at any time, in full or in part, subject to minimum conversion amounts and conditions. After the fourth anniversary of the issuance date, MPLX may convert the Series A preferred units into common units at any time, in whole or in part, subject to certain minimum conversion amounts and conditions, if the closing price of MPLX common units is greater than $48.75 for the 20-day trading period immediately preceding the conversion notice date. The conversion rate for the Series A preferred units shall be the quotient of (a) the sum of (i) $32.50, plus (ii) any unpaid cash distributions on the applicable preferred unit, divided by (b) $32.50, subject to adjustment for unit distributions, unit splits and similar transactions. The holders of the Series A preferred units are entitled to vote on an as-converted basis with the common unitholders and have certain other class voting rights with respect to any amendment to the MPLX partnership agreement that would adversely affect any rights, preferences or privileges of the preferred units. In addition, upon certain events involving a change of control, the holders of preferred units may elect, among other potential elections, to convert their Series A preferred units to common units at the then applicable change of control conversion rate.
Partners' Capital Account, Units			29,500,000
Subsequent Event
Redeemable Noncontrolling Interest [Line Items]
Distribution made to limited partner, declaration date	Jan. 25, 2022
Distribution Made to Limited Partner, Distributions Declared, Per Unit	$ 0.7050
[1]	2021 period includes the Special Distribution Amount.

Segment Information (Details)

Segment Information (Details)	12 Months Ended
	Dec. 31, 2021
Segment Reporting Information [Line Items]
Number of reportable segments	2

Segment Information - Revenues

Segment Information - Revenues and Adjusted EBITDA (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting, Revenue Reconciling Item [Line Items]
Income (Loss) from Equity Method Investments		$ 321	$ (936)	$ 290
Restructuring Charges		0	37	0
Investments in unconsolidated affiliates		(151)	(266)	(713)
Total segment revenues and other income		10,027	7,569	9,041
Marathon Petroleum Corporation [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales-type Lease, Revenue		435	152	7
Restructuring Charges		0	37
Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted EBITDA		5,560	5,211	4,334
Segment Reconciling Items
Segment Reporting, Revenue Reconciling Item [Line Items]
Income (Loss) from Equity Method Investments		321	(936)	290
Restructuring Charges		0	(37)	0
Logistics and Storage [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		3,932	3,940	3,856
Logistics and Storage [Member] | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Lease, Lease Income		772	985	1,235
Income (Loss) from Equity Method Investments		153	154	200
Other Operating Income		61	54	54
Adjusted EBITDA	[1]	3,681	3,488	2,748
Restructuring Charges		0	29	0
Capital Expenditure	[2]	316	498	1,060
Investments in unconsolidated affiliates		(33)	(141)	(289)
Total segment revenues and other income	[3]	5,353	5,285	5,352
Logistics and Storage [Member] | Operating Segments | Marathon Petroleum Corporation [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales-type Lease, Revenue		435	152	7
Gathering and Processing [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		4,089	2,956	3,185
Gathering and Processing [Member] | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Lease, Lease Income		347	365	349
Income (Loss) from Equity Method Investments		168	(1,090)	90
Other Operating Income		70	53	65
Adjusted EBITDA	[1]	1,879	1,723	1,586
Restructuring Charges		0	8	0
Capital Expenditure	[2]	224	441	1,203
Investments in unconsolidated affiliates		(118)	(125)	(424)
Total segment revenues and other income	[3]	4,674	2,284	3,689
Service [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		2,313	2,397	2,498
Service [Member] | Logistics and Storage [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		310	333	346
Service [Member] | Logistics and Storage [Member] | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		3,918	3,889	3,765
Service [Member] | Gathering and Processing [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		2,003	2,064	2,152
Service [Member] | Gathering and Processing [Member] | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		2,023	2,088	2,188
Product [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		1,590	636	806
Product [Member] | Logistics and Storage [Member] | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		14	51	91
Product [Member] | Gathering and Processing [Member] | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		2,066	868	997
Third Party | Logistics and Storage [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total segment revenues and other income		503	567	660
Third Party | Gathering and Processing [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total segment revenues and other income		$ 4,463	$ 2,088	$ 3,474
[1]	See below for the reconciliation from Segment Adjusted EBITDA to “Net income/(loss).”
[2]	Capital expenditures do not include adjustments for asset retirement expenditures.
[3]	Within the total segment revenues and other income amounts presented above, third party revenues for the L&S segment were $503 million, $567 million and $660 million for 2021, 2020 and 2019, respectively. Third party revenues for the G&P segment were $4,463 million, $2,088 million and $3,474 million for 2021, 2020 and 2019, respectively.

Segment Information - Assets by

Segment Information - Assets by Segment (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting, Asset Reconciling Item [Line Items]
Cash and Cash Equivalents, at Carrying Value	$ 13	$ 15
Total assets	35,507	36,414
Operating Segments | Logistics and Storage [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	20,655	20,938
Operating Segments | Gathering and Processing [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 14,839	$ 15,461

Segment Information - Reconcili

Segment Information - Reconciliation Adjusted EBITDA to Net income (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Cost, Depreciation and Amortization		$ 1,287	$ 1,377	$ 1,254
Income Tax Expense (Benefit)		1	2	0
Amortization of deferred financing costs		70	61	42
Asset Impairment Charges		(42)	(2,165)	(1,197)
Income (Loss) from Equity Method Investments		321	(936)	290
Distributions from unconsolidated affiliates		508	459	525
Restructuring Charges		0	37	0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		3,112	(687)	1,462
Logistics and Storage [Member]
Segment Reporting Information [Line Items]
Cost, Depreciation and Amortization		546	633	503
Gathering and Processing [Member]
Segment Reporting Information [Line Items]
Cost, Depreciation and Amortization		741	744	751
Operating Segments
Segment Reporting Information [Line Items]
Adjusted EBITDA		5,560	5,211	4,334
Operating Segments | Logistics and Storage [Member]
Segment Reporting Information [Line Items]
Adjusted EBITDA	[1]	3,681	3,488	2,748
Income (Loss) from Equity Method Investments		153	154	200
Restructuring Charges		0	29	0
Operating Segments | Gathering and Processing [Member]
Segment Reporting Information [Line Items]
Adjusted EBITDA	[1]	1,879	1,723	1,586
Income (Loss) from Equity Method Investments		168	(1,090)	90
Restructuring Charges		0	8	0
Segment Reconciling Items
Segment Reporting Information [Line Items]
Cost, Depreciation and Amortization	[2]	1,287	1,377	1,254
Income Tax Expense (Benefit)		1	2	0
Amortization of deferred financing costs		70	61	42
Extinguishment of Debt, Gain (Loss), Net of Tax		10	19	0
Total compensation expense		(9)	(14)	(22)
Asset Impairment Charges		(42)	(2,165)	(1,197)
Interest and Other Financial Costs		819	854	873
Income (Loss) from Equity Method Investments		321	(936)	290
Distributions from unconsolidated affiliates		537	499	562
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	[3]	(45)	(3)	1
Acquisition Costs, Period Cost		0	0	(14)
Restructuring Charges		0	(37)	0
Other Cost and Expense, Operating		(8)	(6)	(1)
Adjusted EBITDA attributable to noncontrolling interests		39	37	32
Adjusted EBITDA attributable to Predecessor		$ 0	$ 0	$ 770	[4]
[1]	See below for the reconciliation from Segment Adjusted EBITDA to “Net income/(loss).”
[2]	Depreciation and amortization attributable to L&S was $546 million, $633 million and $503 million for the years ended 2021, 2020 and 2019, respectively. Depreciation and amortization attributable to G&P was $741 million, $744 million and $751 million for 2021, 2020 and 2019, respectively.
[3]	MPLX makes 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.
[4]	The Adjusted EBITDA adjustments related to Predecessor are excluded from Adjusted EBITDA attributable to MPLX LP prior to the acquisition date.

Major Customers and Concentra_2

Major Customers and Concentration of Credit Risk (Details) - First Major Customer - Marathon Petroleum Corporation [Member] - Revenues And Other Income] - Customer Concentration Risk		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Concentration Risk [Line Items]
Concentration risk, percentage	[1]	50.00%	55.00%	53.00%
Logistics and Storage [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	[1]	90.00%	89.00%	88.00%
Gathering and Processing [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	[1]	3.00%	4.00%	4.00%
[1]	The percent calculations exclude losses attributable to the impairment of equity method investments.

Inventories (Summary of Invento

Inventories (Summary of Inventories) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Inventory Disclosure [Abstract]
NGLs	$ 12	$ 5
Line fill	23	13
Spare parts, materials and supplies	107	100
Total inventories	$ 142	$ 118

Property, Plant and Equipment_2

Property, Plant and Equipment (Summary of Property, Plant and Equipment) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		$ 26,546	$ 26,875
Total property, plant and equipment	[1]	6,504	5,657
Less accumulated depreciation(1)		20,042	21,218
Logistics and Storage [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		12,371	12,813
Gathering and Processing [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		14,175	14,062
Gas Gathering And Transmission Equipment And Facilities [Member] | Gathering and Processing [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		7,668	7,547
Processing, Fractionation And Storage Facilities [Member] | Gathering and Processing [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		5,795	5,721
Pipelines And Related Assets [Member] | Logistics and Storage [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		6,299	6,026
Barges and towing vessels [Member] | Logistics and Storage [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		965	965
Terminals and related assets [Member] | Logistics and Storage [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		1,655	1,643
Refineries and related assets [Member] | Logistics and Storage [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		1,650	2,333
Land Building Office Equipment And Other [Member] | Logistics and Storage [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		1,589	1,584
Land Building Office Equipment And Other [Member] | Gathering and Processing [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		514	507
Construction-in-progress | Logistics and Storage [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		213	262
Construction-in-progress | Gathering and Processing [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		$ 198	$ 287
Minimum | Gas Gathering And Transmission Equipment And Facilities [Member] | Gathering and Processing [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives		5 years
Minimum | Processing, Fractionation And Storage Facilities [Member] | Gathering and Processing [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives		10 years
Minimum | Pipelines And Related Assets [Member] | Logistics and Storage [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives		3 years
Minimum | Barges and towing vessels [Member] | Logistics and Storage [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives		15 years
Minimum | Terminals and related assets [Member] | Logistics and Storage [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives		4 years
Minimum | Refineries and related assets [Member] | Logistics and Storage [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives		13 years
Minimum | Land Building Office Equipment And Other [Member] | Logistics and Storage [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives		2 years
Minimum | Land Building Office Equipment And Other [Member] | Gathering and Processing [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives		3 years
Maximum | Gas Gathering And Transmission Equipment And Facilities [Member] | Gathering and Processing [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives		40 years
Maximum | Processing, Fractionation And Storage Facilities [Member] | Gathering and Processing [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives		40 years
Maximum | Pipelines And Related Assets [Member] | Logistics and Storage [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives		50 years
Maximum | Barges and towing vessels [Member] | Logistics and Storage [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives		20 years
Maximum | Terminals and related assets [Member] | Logistics and Storage [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives		40 years
Maximum | Refineries and related assets [Member] | Logistics and Storage [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives		40 years
Maximum | Land Building Office Equipment And Other [Member] | Logistics and Storage [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives		60 years
Maximum | Land Building Office Equipment And Other [Member] | Gathering and Processing [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives		40 years
[1]	Includes property, plant and equipment impairment charges recorded during the respective period, as discussed below.

Property Plant and Equipment (N

Property Plant and Equipment (Narrative) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Accumulated depreciation	[1]	$ 6,504	$ 5,657
Impairment of Long-Lived Assets Held-for-use		$ 42	$ 174
[1]	Includes property, plant and equipment impairment charges recorded during the respective period, as discussed below.

Goodwill and Intangibles (Goodw

Goodwill and Intangibles (Goodwill) (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Goodwill [Line Items]
Goodwill, Impairment Loss	$ 0	$ 1,814
Number of reporting units	3
Goodwill	$ 7,657	7,657	$ 9,536
Impairment of Intangible Assets, Finite-lived		177
Total Number of Reporting Units	5
Gathering and Processing [Member]
Goodwill [Line Items]
Goodwill, Impairment Loss	$ 0	1,814	1,197
Goodwill	$ 0	$ 0	$ 1,814
Measurement Input, Discount Rate [Member] | Goodwill | Income Approach Valuation Technique
Goodwill [Line Items]
Fair Value Inputs	7.20%
Measurement Input, Discount Rate [Member] | Goodwill | Income Approach Valuation Technique | Minimum
Goodwill [Line Items]
Fair Value Inputs		9.50%
Measurement Input, Discount Rate [Member] | Goodwill | Income Approach Valuation Technique | Maximum
Goodwill [Line Items]
Fair Value Inputs		11.50%
Crude Gathering [Member]
Goodwill [Line Items]
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount	23.00%
Transportation and Storage
Goodwill [Line Items]
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount	51.00%

Goodwill and Intangibles (Recon

Goodwill and Intangibles (Reconciliation of Goodwill) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Goodwill [Line Items]
Gross goodwill	$ 10,798		$ 10,863
Accumulated impairment losses	(3,141)		(1,327)
Goodwill, beginning balance	7,657	$ 9,536
Impairment losses	0	(1,814)
Goodwill, ending balance	7,657	7,657	9,536
Western Refining Wholesale & Western Refining Product Transport [Member]
Goodwill [Line Items]
Goodwill, Written off Related to Sale of Business Unit		65
Logistics and Storage [Member]
Goodwill [Line Items]
Gross goodwill	7,657		7,722
Accumulated impairment losses	0		0
Goodwill, beginning balance	7,657	7,722
Impairment losses	0	0
Goodwill, ending balance	7,657	7,657	7,722
Logistics and Storage [Member] | Western Refining Wholesale & Western Refining Product Transport [Member]
Goodwill [Line Items]
Goodwill, Written off Related to Sale of Business Unit		65
Gathering and Processing [Member]
Goodwill [Line Items]
Gross goodwill	3,141		3,141
Accumulated impairment losses	(3,141)		(1,327)
Goodwill, beginning balance	0	1,814
Impairment losses	0	(1,814)	(1,197)
Goodwill, ending balance	$ 0	0	$ 1,814
Gathering and Processing [Member] | Western Refining Wholesale & Western Refining Product Transport [Member]
Goodwill [Line Items]
Goodwill, Written off Related to Sale of Business Unit		$ 0

Goodwill and Intangibles (Intan

Goodwill and Intangibles (Intangible Assets) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Gross		$ 1,571	$ 1,571
Accumulated amortization	[1]	(740)	(612)	[2]
Intangible Assets, Net (Excluding Goodwill)		831	959
Impairment of Intangible Assets, Finite-lived			177
Logistics and Storage [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization of Intangible Assets		36	36
Gross		283	283
Accumulated amortization	[1]	(117)	(81)
Intangible Assets, Net (Excluding Goodwill)		$ 166	202
Logistics and Storage [Member] | Minimum
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		6 years
Logistics and Storage [Member] | Maximum
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		8 years
Gathering and Processing [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization of Intangible Assets		$ 92	98
Gross		1,288	1,288
Accumulated amortization	[1]	(623)	(531)	[2]
Intangible Assets, Net (Excluding Goodwill)		$ 665	$ 757
Gathering and Processing [Member] | Minimum
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		6 years
Gathering and Processing [Member] | Maximum
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		25 years
[1]	Amortization expense attributable to the G&P segment for the years ended December 31, 2021 and 2020 was $92 million and $98 million, respectively. Amortization expense attributable to the L&S segment for both years ended December 31, 2021 and 2020 was $36 million.
[2]	Impairment charge of $177 million is included within the G&P accumulated amortization for the year ended December 31, 2020.

Goodwill and Intangibles (Futur

Goodwill and Intangibles (Future Amortization Expense) (Details) $ in Millions	Dec. 31, 2021USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2018	$ 127
2019	127
2020	127
2021	113
2022	104
Thereafter	233
Total future intangibles amortization expenses	$ 831

Fair Value Measurements - Recur

Fair Value Measurements - Recurring (Financial Instruments by Valuation Hierarchy) (Details) - Fair Value, Recurring [Member] - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	$ 0	$ 0
Liabilities	(108)	(63)
Embedded derivatives in commodity contracts | Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0	0
Liabilities	$ (108)	$ (63)

Fair Value Measurements - Rec_2

Fair Value Measurements - Recurring (Significant Unobservable Inputs in Level 3 Valuation) (Details)	12 Months Ended
	Dec. 31, 2021USD ($)$ / gal
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Derivative, Average Forward Price | $ / gal	0.92
Significant unobservable inputs (Level 3)
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Embedded Derivative Renewal Term	5 years
Significant unobservable inputs (Level 3) | Commodity contracts | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs commodity price	$ 0.72
Significant unobservable inputs (Level 3) | Commodity contracts | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs commodity price	$ 1.79
Significant unobservable inputs (Level 3) | Embedded derivatives in commodity contracts
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Probability of Renewal	100.00%

Fair Value Measurements - Rec_3

Fair Value Measurements - Recurring (Changes in Level 3 Measurements) (Details) - Embedded Derivatives in Commodity Contracts (net) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Fair value at beginning of period		$ (63)	$ (60)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings	[1]	(59)	(9)
Settlements		14	6
Fair value at end of period		(108)	(63)
The amount of total losses for the period included in earnings attributable to the change in unrealized gains or losses relating to liabilities still held at end of period		$ (47)	$ (4)
[1]	Losses 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		Dec. 31, 2021	Dec. 31, 2020
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding debt(1)	[1]	$ 20,779	$ 22,951
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Outstanding debt(1)	[1]	$ 18,664	$ 20,244
[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 in natural gas processing and purchase contract [Member] - Embedded derivatives in commodity contracts $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)
Derivative [Line Items]
Number of renewals	1
Term of counterparty option to renew gas purchase agreement	5 years
Embedded derivative fair value of embedded derivative liability including inception value allocable to host contract	$ 108	$ 63

Derivative Financial Instrume_4

Derivative Financial Instruments (Derivatives Balance Sheet Location) (Details) - Commodity contracts - USD ($) $ in Millions		Dec. 31, 2021	Dec. 31, 2020
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset		$ 0	$ 0
Derivative liability, fair value, gross liability	[1]	(108)	(63)
Not Designated as Hedging Instrument | Other current assets
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset		0	0
Not Designated as Hedging Instrument | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, fair value, gross liability	[1]	(15)	(7)
Not Designated as Hedging Instrument | Other noncurrent assets
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset		0	0
Not Designated as Hedging Instrument | Other Noncurrent Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liability, fair value, gross liability	[1]	$ (93)	$ (56)
[1]	Includes the embedded derivative in the commodity contract discussed above.

Derivative Financial Instrume_5

Derivative Financial Instruments (Derivatives Income Statement Location) (Details) - Purchased product costs - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Realized gains	$ (14)	$ (6)	$ (6)
Total derivative loss	(59)	(9)	(5)
Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	$ (45)	$ (3)	$ 1

Debt (Summary of Outstanding Bo

Debt (Summary of Outstanding Borrowings) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Jan. 15, 2021	Dec. 31, 2020	Oct. 15, 2020	Sep. 14, 2020	Aug. 31, 2020	Aug. 18, 2020	Sep. 09, 2019
Debt Instrument [Line Items]
Finance Lease, Liability		$ 9
Debt and capital lease obligations		18,909		$ 20,536
Unamortized debt issuance costs		102		116
Unamortized discount		236		281
Debt, Current		499		764
Total long-term debt due after one year		18,072		19,375
MPLX Revolving Credit Facility due July 2024 [Member]
Debt Instrument [Line Items]
Outstanding balance		300		175
Term loan facility due 2019
Debt Instrument [Line Items]
Outstanding balance								$ 1,000
Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross									$ 2,000
Senior Notes | Floating Rate Senior Notes Due September 2021 [Member]
Debt Instrument [Line Items]
Long-term debt, gross						$ 1,000			1,000
Senior Notes | Floating Rate Senior Notes Due September 2022 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 0		1,000					$ 1,000
Debt Instrument, Maturity Date		Sep. 9, 2022
Finance Lease [Member]
Debt Instrument [Line Items]
Finance Lease, Liability	[1]	$ 9		11
MPLX LP | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross								3,000
MPLX LP | Senior Notes | Senior Notes Due October 2022 [Member]
Debt Instrument [Line Items]
Long-term debt, gross					$ 300
Interest rate, stated percentage					6.25%
MPLX LP | Senior Notes | Senior Notes Due December 2022 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 486		486
Debt Instrument, Maturity Date		Dec. 1, 2022
Interest rate, stated percentage		3.50%
MPLX LP | Senior Notes | Senior Notes Due March 2023 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 500		500
Debt Instrument, Maturity Date		Mar. 15, 2023
Interest rate, stated percentage		3.375%
MPLX LP | Senior Notes | Senior Notes Due July 2023 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 989		989
Debt Instrument, Maturity Date		Jul. 15, 2023
Interest rate, stated percentage		4.50%
MPLX LP | Senior Notes | Senior Notes Due May 2024 [Member]
Debt Instrument [Line Items]
Long-term debt, gross							$ 450
Interest rate, stated percentage							6.375%
MPLX LP | Senior Notes | Senior Notes Due December 2024 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 1,149		1,149
Debt Instrument, Maturity Date		Dec. 1, 2024
Interest rate, stated percentage		4.875%
MPLX LP | Senior Notes | Senior Notes Due January 2025 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 0	$ 750	708
Debt Instrument, Maturity Date		Jan. 15, 2025
Interest rate, stated percentage		5.25%	5.25%
MPLX LP | Senior Notes | Senior Notes Due February 2025 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 500		500
Debt Instrument, Maturity Date		Feb. 15, 2025
Interest rate, stated percentage		4.00%
MPLX LP | Senior Notes | Senior Notes Due June 2025 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 1,189		1,189
Debt Instrument, Maturity Date		Jun. 1, 2025
Interest rate, stated percentage		4.875%
MPLX LP | Senior Notes | 4.125% senior notes due March 2027
Debt Instrument [Line Items]
Long-term debt, gross		$ 1,250		1,250
Debt Instrument, Maturity Date		Mar. 1, 2027
Interest rate, stated percentage		4.125%
MPLX LP | Senior Notes | Senior Notes Due December 2027 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 732		732
Debt Instrument, Maturity Date		Dec. 1, 2027
Interest rate, stated percentage		4.25%
MPLX LP | Senior Notes | Senior Notes Due March 2028 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 1,250		1,250
Debt Instrument, Maturity Date		Mar. 15, 2028
Interest rate, stated percentage		4.00%
MPLX LP | Senior Notes | Senior Notes Due February 2029 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 750		750
Debt Instrument, Maturity Date		Feb. 15, 2029
Interest rate, stated percentage		4.80%
MPLX LP | Senior Notes | Senior Notes Due April 2038 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 1,750		1,750
Debt Instrument, Maturity Date		Apr. 15, 2038
Interest rate, stated percentage		4.50%
MPLX LP | Senior Notes | 5.200% senior notes due March 2047
Debt Instrument [Line Items]
Long-term debt, gross		$ 1,000		1,000
Debt Instrument, Maturity Date		Mar. 1, 2047
Interest rate, stated percentage		5.20%
MPLX LP | Senior Notes | Senior Notes Due December 2047 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 487		487
Debt Instrument, Maturity Date		Dec. 1, 2047
Interest rate, stated percentage		5.20%
MPLX LP | Senior Notes | Senior Notes Due April 2048 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 1,500		1,500
Debt Instrument, Maturity Date		Apr. 15, 2048
Interest rate, stated percentage		4.70%
MPLX LP | Senior Notes | Senior Notes Due February 2049 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 1,500		1,500
Debt Instrument, Maturity Date		Feb. 15, 2049
Interest rate, stated percentage		5.50%
MPLX LP | Senior Notes | Senior Notes Due April 2058 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 500		500
Debt Instrument, Maturity Date		Apr. 15, 2058
Interest rate, stated percentage		4.90%
MPLX LP | Senior Notes | Senior Notes Due August 2030 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 1,500		1,500				$ 1,500
Debt Instrument, Maturity Date		Aug. 15, 2030
Interest rate, stated percentage		2.65%						2.65%
MPLX LP | Senior Notes | Senior Notes Due March 2026 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 1,500		1,500				$ 1,500
Debt Instrument, Maturity Date		Mar. 1, 2026
Interest rate, stated percentage		1.75%						1.75%
MarkWest | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross		$ 23		23
ANDX LP [Member] | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross		$ 45		$ 87
ANDX LP [Member] | Senior Notes | Senior Notes Due October 2022 [Member]
Debt Instrument [Line Items]
Long-term debt, gross					$ 34
ANDX LP [Member] | Senior Notes | Senior Notes Due May 2024 [Member]
Debt Instrument [Line Items]
Long-term debt, gross							$ 69
ANDX LP [Member] | Senior Notes | Senior Notes Due January 2025 [Member]
Debt Instrument [Line Items]
Long-term debt, gross			$ 42
[1]	See Note 20 for lease information.

Debt (Summary of Outstanding _2

Debt (Summary of Outstanding Borrowings Interest Rates and Table Due Dates) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Jan. 15, 2021	Dec. 31, 2020	Oct. 15, 2020	Sep. 14, 2020	Aug. 31, 2020	Aug. 18, 2020	Sep. 09, 2019
Line of Credit | MPLX Revolving Credit Facility due July 2024 [Member]
Debt Instrument [Line Items]
Expiration date	Jul. 30, 2024
Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross								$ 2,000
Senior Notes | Senior Notes Due March 2023 [Member]
Debt Instrument [Line Items]
Long-term debt, gross					$ 1,000			1,000
Senior Notes | Floating Rate Senior Notes Due September 2022 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date	Sep. 9, 2022
Long-term debt, gross	$ 0		$ 1,000					$ 1,000
MPLX LP | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross							$ 3,000
MPLX LP | Senior Notes | 4.875% senior notes due December 2024
Debt Instrument [Line Items]
Interest rate, stated percentage				6.25%
Long-term debt, gross				$ 300
MPLX LP | Senior Notes | 4.000% senior notes due February 2025
Debt Instrument [Line Items]
Interest rate, stated percentage	3.50%
Debt Instrument, Maturity Date	Dec. 1, 2022
Long-term debt, gross	$ 486		486
MPLX LP | Senior Notes | 4.875% senior notes due June 2025
Debt Instrument [Line Items]
Interest rate, stated percentage	3.375%
Debt Instrument, Maturity Date	Mar. 15, 2023
Long-term debt, gross	$ 500		500
MPLX LP | Senior Notes | Senior Notes Due July 2023 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	4.50%
Debt Instrument, Maturity Date	Jul. 15, 2023
Long-term debt, gross	$ 989		989
MPLX LP | Senior Notes | Senior Notes Due March 2028 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	4.00%
Debt Instrument, Maturity Date	Mar. 15, 2028
Long-term debt, gross	$ 1,250		1,250
MPLX LP | Senior Notes | Senior Notes Due February 2029 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	4.80%
Debt Instrument, Maturity Date	Feb. 15, 2029
Long-term debt, gross	$ 750		750
MPLX LP | Senior Notes | Senior Notes Due April 2038 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	4.50%
Debt Instrument, Maturity Date	Apr. 15, 2038
Long-term debt, gross	$ 1,750		1,750
MPLX LP | Senior Notes | 5.200% senior notes due March 2047
Debt Instrument [Line Items]
Interest rate, stated percentage	5.20%
Debt Instrument, Maturity Date	Mar. 1, 2047
Long-term debt, gross	$ 1,000		1,000
MPLX LP | Senior Notes | Senior Notes Due April 2048 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	4.70%
Debt Instrument, Maturity Date	Apr. 15, 2048
Long-term debt, gross	$ 1,500		1,500
MPLX LP | Senior Notes | Senior Notes Due November 2049 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	5.50%
Debt Instrument, Maturity Date	Feb. 15, 2049
Long-term debt, gross	$ 1,500		1,500
MPLX LP | Senior Notes | Senior Notes Due April 2058 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	4.90%
Debt Instrument, Maturity Date	Apr. 15, 2058
Long-term debt, gross	$ 500		500
MPLX LP | Senior Notes | Senior Notes Due May 2024 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage						6.375%
Long-term debt, gross						$ 450
MPLX LP | Senior Notes | Senior Notes Due December 2024 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	4.875%
Debt Instrument, Maturity Date	Dec. 1, 2024
Long-term debt, gross	$ 1,149		1,149
MPLX LP | Senior Notes | Senior Notes Due January 2025 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	5.25%	5.25%
Debt Instrument, Maturity Date	Jan. 15, 2025
Long-term debt, gross	$ 0	$ 750	708
MPLX LP | Senior Notes | Senior Notes Due February 2025 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	4.00%
Debt Instrument, Maturity Date	Feb. 15, 2025
Long-term debt, gross	$ 500		500
MPLX LP | Senior Notes | Senior Notes Due June 2025 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	4.875%
Debt Instrument, Maturity Date	Jun. 1, 2025
Long-term debt, gross	$ 1,189		1,189
MPLX LP | Senior Notes | Senior Notes Due March 2027 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	4.125%
Debt Instrument, Maturity Date	Mar. 1, 2027
Long-term debt, gross	$ 1,250		1,250
MPLX LP | Senior Notes | Senior Notes Due December 2027 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	4.25%
Debt Instrument, Maturity Date	Dec. 1, 2027
Long-term debt, gross	$ 732		732
MPLX LP | Senior Notes | Senior Notes Due December 2047 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	5.20%
Debt Instrument, Maturity Date	Dec. 1, 2047
Long-term debt, gross	$ 487		487
MPLX LP | Senior Notes | Senior Notes Due March 2026 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	1.75%						1.75%
Debt Instrument, Maturity Date	Mar. 1, 2026
Long-term debt, gross	$ 1,500		1,500				$ 1,500
MPLX LP | Senior Notes | Senior Notes Due August 2030 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	2.65%						2.65%
Debt Instrument, Maturity Date	Aug. 15, 2030
Long-term debt, gross	$ 1,500		1,500				$ 1,500
MarkWest | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 23		23
MarkWest | Senior Notes | Senior Notes Due July 2023 [Member] | Minimum
Debt Instrument [Line Items]
Interest rate, stated percentage	4.50%
Debt Instrument, Maturity Date	Jul. 15, 2023
MarkWest | Senior Notes | Senior Notes Due June 2025 [Member] | Maximum
Debt Instrument [Line Items]
Interest rate, stated percentage	4.875%
Debt Instrument, Maturity Date	Jun. 1, 2025
ANDX LP [Member] | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 45		$ 87
ANDX LP [Member] | Senior Notes | 4.875% senior notes due December 2024
Debt Instrument [Line Items]
Long-term debt, gross				$ 34
ANDX LP [Member] | Senior Notes | 4.000% senior notes due February 2025 | Minimum
Debt Instrument [Line Items]
Interest rate, stated percentage	3.50%
Debt Instrument, Maturity Date	Dec. 1, 2022
ANDX LP [Member] | Senior Notes | Senior Notes Due May 2024 [Member]
Debt Instrument [Line Items]
Long-term debt, gross						$ 69
ANDX LP [Member] | Senior Notes | Senior Notes Due January 2025 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 42
ANDX LP [Member] | Senior Notes | Senior Notes Due January 2025 [Member] | Maximum
Debt Instrument [Line Items]
Interest rate, stated percentage	5.20%
ANDX LP [Member] | Senior Notes | Senior Notes Due December 2047 [Member] | Maximum
Debt Instrument [Line Items]
Debt Instrument, Maturity Date	Dec. 1, 2047

Debt (Schedule of Debt Payments

Debt (Schedule of Debt Payments) (Detail) $ in Millions	Dec. 31, 2021USD ($)
Debt Disclosure [Abstract]
2020	$ 502
2021	1,502
2022	1,451
2023	1,701
2024	$ 1,501

Debt (Credit Agreements) (Detai

Debt (Credit Agreements) (Detail) $ in Millions	Sep. 26, 2019USD ($)	Sep. 09, 2019USD ($)	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Sep. 14, 2020USD ($)	Aug. 18, 2020USD ($)
Debt Instrument [Line Items]
Proceeds from long-term lines of credit			$ 4,175	$ 6,810	$ 9,174
MPLX Revolving Credit Facility due July 2024 [Member]
Debt Instrument [Line Items]
Proceeds from long-term lines of credit			$ 4,175	$ 3,815
Interest rate, effective percentage			1.343%	1.49%
Repayments of long-term lines of credit			$ 4,050	$ 3,640
Letters of credit outstanding, amount			1	1
Remaining borrowing capacity			$ 3,200	$ 3,325
Remaining borrowing capacity, percentage			91.00%	95.00%
Line of Credit Facility, Current Borrowing Capacity			$ 3,500
Long-term Line of Credit			300	$ 175
MPLX Revolving Credit Facility due July 2024 [Member] | Letter of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity			300
MPLX Revolving Credit Facility due July 2024 [Member] | Swingline Loan
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 150
MPLX Revolving Credit Facility due July 2024 [Member] | MPLX LP
Debt Instrument [Line Items]
Debt Instrument, Description of Variable Rate Basis			Adjusted LIBOR or the Alternate Base Rate (as defined in the MPLX Credit Agreement), at our election, plus a specified margin
Number of prior quarterly reporting periods used in determining compliance with covenant of ratio of consolidated net debt to consolidated EBITDA			4
Covenant of ratio of consolidated net debt to consolidated EBITDA (in ratio)			5
Covenant of ratio of consolidated net debt to consolidated EBITDA following certain acquisitions (in ratio)			5.5
MPLX Revolving Credit Facility due July 2024 [Member] | MPLX LP | Maximum
Debt Instrument [Line Items]
Additional borrowing capacity			$ 1,000
MPLX Revolving Credit Facility due July 2024 [Member] | MPLX LP | Letter of Credit
Debt Instrument [Line Items]
Number of renewals			2
Debt Instrument, Renewal Term			1 year
Debt Instrument, Second Renewal Term [Line Items]			1 year
Term loan facility due 2019
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 1,000						$ 1,000
Debt Instrument, Description of Variable Rate Basis	(i) the Adjusted LIBO Rate (as defined in the Term Loan Agreement) plus a margin ranging from 75.0 basis points to 100.0 basis points per annum, depending on MPLX’s credit ratings or (ii) the Alternate Base Rate (as defined in the Term Loan Agreement)
Long-term Line of Credit							1,000
Senior Notes
Debt Instrument [Line Items]
Long-term debt, outstanding		$ 2,000
Senior Notes | MPLX LP
Debt Instrument [Line Items]
Long-term debt, outstanding							$ 3,000
Senior Notes | ANDX LP [Member]
Debt Instrument [Line Items]
Long-term debt, outstanding			$ 45	$ 87
Senior Notes | Floating Rate Senior Notes Due September 2021 [Member]
Debt Instrument [Line Items]
Debt Instrument, Description of Variable Rate Basis		LIBOR plus 0.9 percent per annum
Long-term debt, outstanding		$ 1,000				$ 1,000

Debt (Senior Notes) (Details)

Debt (Senior Notes) (Details) - USD ($) $ in Millions	Sep. 26, 2019	Sep. 09, 2019	Dec. 31, 2021	Dec. 31, 2020	Jan. 15, 2021	Oct. 15, 2020	Sep. 14, 2020	Aug. 31, 2020	Aug. 18, 2020
MPLX Revolving Credit Facility due July 2024 [Member]
Debt Instrument [Line Items]
Outstanding balance			$ 300	$ 175
Term loan facility due 2019
Debt Instrument [Line Items]
Debt Instrument, Description of Variable Rate Basis	(i) the Adjusted LIBO Rate (as defined in the Term Loan Agreement) plus a margin ranging from 75.0 basis points to 100.0 basis points per annum, depending on MPLX’s credit ratings or (ii) the Alternate Base Rate (as defined in the Term Loan Agreement)
Write off of Deferred Debt Issuance Cost				1
Maximum borrowing capacity	$ 1,000								$ 1,000
Outstanding balance									1,000
Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross		$ 2,000
Percent of par		100.00%
Senior Notes | Floating Rate Senior Notes Due September 2021 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 1,000					$ 1,000
Debt Instrument, Description of Variable Rate Basis		LIBOR plus 0.9 percent per annum
Write off of Deferred Debt Issuance Cost				3
Senior Notes | Floating Rate Senior Notes Due September 2022 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 1,000	0	1,000
Debt Instrument, Description of Variable Rate Basis		LIBOR plus 1.1 percent per annum
Write off of Deferred Debt Issuance Cost			$ 2
MPLX LP | MPLX Revolving Credit Facility due July 2024 [Member]
Debt Instrument [Line Items]
Debt Instrument, Description of Variable Rate Basis			Adjusted LIBOR or the Alternate Base Rate (as defined in the MPLX Credit Agreement), at our election, plus a specified margin
MPLX LP | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross									3,000
MPLX LP | Senior Notes | Senior Notes Due February 2029 [Member]
Debt Instrument [Line Items]
Long-term debt, gross			$ 750	750
Interest rate, stated percentage			4.80%
MPLX LP | Senior Notes | Senior Notes Due February 2049 [Member]
Debt Instrument [Line Items]
Long-term debt, gross			$ 1,500	1,500
Interest rate, stated percentage			5.50%
MPLX LP | Senior Notes | Senior Notes Due March 2023 [Member]
Debt Instrument [Line Items]
Long-term debt, gross			$ 500	500
Interest rate, stated percentage			3.375%
MPLX LP | Senior Notes | 4.125% senior notes due March 2027
Debt Instrument [Line Items]
Long-term debt, gross			$ 1,250	1,250
Interest rate, stated percentage			4.125%
MPLX LP | Senior Notes | 5.200% senior notes due March 2047
Debt Instrument [Line Items]
Long-term debt, gross			$ 1,000	1,000
Interest rate, stated percentage			5.20%
MPLX LP | Senior Notes | Senior Notes Due March 2028 [Member]
Debt Instrument [Line Items]
Long-term debt, gross			$ 1,250	1,250
Interest rate, stated percentage			4.00%
MPLX LP | Senior Notes | Senior Notes Due April 2038 [Member]
Debt Instrument [Line Items]
Long-term debt, gross			$ 1,750	1,750
Interest rate, stated percentage			4.50%
MPLX LP | Senior Notes | Senior Notes Due April 2048 [Member]
Debt Instrument [Line Items]
Long-term debt, gross			$ 1,500	1,500
Interest rate, stated percentage			4.70%
MPLX LP | Senior Notes | Senior Notes Due April 2058 [Member]
Debt Instrument [Line Items]
Long-term debt, gross			$ 500	500
Interest rate, stated percentage			4.90%
MPLX LP | Senior Notes | Senior Notes Due October 2022 [Member]
Debt Instrument [Line Items]
Long-term debt, gross						$ 300
Interest rate, stated percentage						6.25%
Write off of Deferred Debt Issuance Cost				4
MPLX LP | Senior Notes | Senior Notes Due December 2022 [Member]
Debt Instrument [Line Items]
Long-term debt, gross			$ 486	486
Interest rate, stated percentage			3.50%
MPLX LP | Senior Notes | Senior Notes Due May 2024 [Member]
Debt Instrument [Line Items]
Long-term debt, gross								$ 450
Interest rate, stated percentage								6.375%
Percent of par								103.20%
Write off of Deferred Debt Issuance Cost				18
Gain (Loss) on Extinguishment of Debt, before Write off of Debt Issuance Cost				14
MPLX LP | Senior Notes | Senior Notes Due January 2025 [Member]
Debt Instrument [Line Items]
Long-term debt, gross			$ 0	708	$ 750
Interest rate, stated percentage			5.25%		5.25%
Percent of par					10262.50%
Gain (Loss) on Extinguishment of Debt			$ 8
Write off of Deferred Debt Issuance Cost			12
Gain (Loss) on Extinguishment of Debt, before Write off of Debt Issuance Cost			20
MPLX LP | Senior Notes | Senior Notes Due December 2027 [Member]
Debt Instrument [Line Items]
Long-term debt, gross			$ 732	732
Interest rate, stated percentage			4.25%
MPLX LP | Senior Notes | Senior Notes Due December 2047 [Member]
Debt Instrument [Line Items]
Long-term debt, gross			$ 487	487
Interest rate, stated percentage			5.20%
MPLX LP | Senior Notes | Senior Notes Due March 2026 [Member]
Debt Instrument [Line Items]
Long-term debt, gross			$ 1,500	1,500					$ 1,500
Interest rate, stated percentage			1.75%						1.75%
Percent of par									99.785%
MPLX LP | Senior Notes | Senior Notes Due August 2030 [Member]
Debt Instrument [Line Items]
Long-term debt, gross			$ 1,500	1,500					$ 1,500
Interest rate, stated percentage			2.65%						2.65%
Percent of par									99.913%
ANDX LP [Member] | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross			$ 45	87
ANDX LP [Member] | Senior Notes | Senior Notes Due October 2022 [Member]
Debt Instrument [Line Items]
Long-term debt, gross						$ 34
ANDX LP [Member] | Senior Notes | Senior Notes Due May 2024 [Member]
Debt Instrument [Line Items]
Long-term debt, gross								$ 69
ANDX LP [Member] | Senior Notes | Senior Notes Due January 2025 [Member]
Debt Instrument [Line Items]
Long-term debt, gross					$ 42
MarkWest | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross			$ 23	$ 23
Minimum | ANDX LP [Member] | Senior Notes | Senior Notes Due December 2022 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage			3.50%
Maximum | ANDX LP [Member] | Senior Notes | Senior Notes Due January 2025 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage			5.20%
Letter of Credit | MPLX Revolving Credit Facility due July 2024 [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 300
Letter of Credit | MPLX LP | MPLX Revolving Credit Facility due July 2024 [Member]
Debt Instrument [Line Items]
Debt Instrument, Renewal Term			1 year

Revenue Disaggregation of Reven

Revenue Disaggregation of Revenue (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Noninterest Income		$ 8,021	$ 6,896	$ 7,041
Revenue Not from Contract with Customer, Other	[1]	2,006	673	2,000
Revenues		10,027	7,569	9,041
Service [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		2,313	2,397	2,498
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		3,628	3,580	3,455
Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		345	155	140
Product [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		1,590	636	806
Revenue from Contract with Customer, excluding Assessed Tax and Non-ASC 606 Revenue		1,590	636	806
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		145	128	142
Logistics and Storage [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		3,932	3,940	3,856
Logistics and Storage [Member] | Service [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		310	333	346
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		3,608	3,556	3,419
Logistics and Storage [Member] | Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		0	0	0
Logistics and Storage [Member] | Product [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, excluding Assessed Tax and Non-ASC 606 Revenue		4	39	65
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		10	12	26
Gathering and Processing [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		4,089	2,956	3,185
Gathering and Processing [Member] | Service [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		2,003	2,064	2,152
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		20	24	36
Gathering and Processing [Member] | Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		345	155	140
Gathering and Processing [Member] | Product [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, excluding Assessed Tax and Non-ASC 606 Revenue		1,586	597	741
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		$ 135	$ 116	$ 116
[1]	Non-ASC 606 Revenue includes rental income, sales-type lease revenue, income/(loss) from equity method investments, derivative gains and losses, mark-to-market adjustments, and other income.

Revenue Contract Balance Rollfo

Revenue Contract Balance Rollforward (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Beginning Balance Deferred Revenue, Noncurrent		$ 314
Ending Balance Deferred Revenue, Noncurrent		383	$ 314
Contract with Customer, Liability, Change in Timeframe, Performance Obligation Satisfied, Revenue Recognized		0	0
Accounting Standards Update 2014-09 [Member]
Beginning Balance Contract with Customer, Asset, Gross	[1]	40	39
Contract with Customer, Asset Increase (Decrease)		(15)	3
Contract with Customer, Asset, Reclassified to Receivable	[2]	0	(2)
Ending Balance Contract with Customer, Asset, Gross	[1]	25	40
Contract with Customer, Non Current Asset Reclassified to Receivable	[2]	0	0
Contract with Customer, Asset Increase (Decrease), Noncurrent		0	2
Contract with Customer, Asset, before Allowance for Credit Loss, Noncurrent	[1]	2	2	$ 0
Beginning Balance Deferred Revenue, Current	[1]	37	23
Deferred Revenue, Period Increase (Decrease)		56	22
Deferred Revenue, Revenue Recognized	[2]	(37)	(8)
Ending Balance Deferred Revenue, Current	[1]	56	37
Beginning Balance Deferred revenue - related parties	[1]	91	53
Deferred Revenue - Related Party, Period Increase (Decrease)		75	121
Deferred Revenue - Related Parties, Revenue Recognized	[2]	(106)	(83)
Ending Balance Deferred Revenue, Current, Related Parties	[1]	60	91
Beginning Balance Deferred Revenue, Noncurrent	[1]	119	90
Deferred Revenue, Noncurrent, Period Increase (Decrease)		16	29
Deferred Revenue, Noncurrent, Revenue Recognized	[2]	0	0
Ending Balance Deferred Revenue, Noncurrent	[1]	135	119
Beginning Balance Deferred Revenue, Noncurrent, Related Parties	[1]	48	55
Deferred Revenue, Noncurrent, Related Party, Period Increase (Decrease)		(17)	(7)
Deferred Revenue, Noncurrent, Related Parties, Revenue Recognized	[2]	0	0
Ending Balance Deferred Revenue, Noncurrent, Related Parties	[1]	31	48
Contract Liability, Noncurrent, Revenue Recognized	[2]	0	0
Contract Liability, Noncurrent, Period Increase (Decrease) [Line Items]		(1)	6
Contract with Customer, Liability, Noncurrent	[1]	$ 5	$ 6	$ 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	Dec. 31, 2021USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Contract with Customer, Liability	$ 281
Revenue, Remaining Performance Obligation, Amount	9,957	[1],[2],[3]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 1,850
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 1,725
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	2 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 1,592
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	3 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 1,507
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	4 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 3,283
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	5 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]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	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, see further discussion about leases in Note 20.
[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		12 Months Ended
	Jun. 30, 2021	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Supplemental Cash Flow Information [Abstract]
Interest paid (net of amounts capitalized)			$ 812	$ 821	$ 835
Income taxes paid			4	2	1
Operating Lease, Payments			79	87	85
Finance Lease, Interest Expense			0	1	1
Finance Lease, Principal Payments			2	9	5
Non-cash investing and financing activities:
Net transfers of property, plant and equipment from materials and supplies inventories			1	0	2
Sales-type Lease, Selling Profit (Loss)	$ 112	$ 209	0	0	21
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability			20	17	26
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability			0	1	4
Fair Value of Units Redeemed			0	340	0
Contribution - common units issued			$ 0	$ 0	$ 7,722	[1]
[1]	For 2019, includes limited partner units issued to MPC and public unitholders as consideration in the Merger. See Note 4.

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	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Supplemental Cash Flow Information [Abstract]
(Decrease)/increase in capital accruals	$ 11	$ (244)	$ (146)

Leases Lessee Disclosures (Deta

Leases Lessee Disclosures (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Finance Lease, Liability, to be Paid, Year One		$ 2
Finance Lease, Liability, to be Paid, Year Two		2
Finance Lease, Liability, to be Paid, Year Three		1
Finance Lease, Liability, to be Paid, Year Four		1
Finance Lease, Liability, to be Paid, Year Five		1
Finance Lease, Liability, to be Paid, after Year Five		8
Finance Lease, Liability, Payment, Due		15
Finance Lease, Liability, Undiscounted Excess Amount		6
Finance Lease, Interest Expense		0	$ 1	$ 1
Property, plant and equipment, gross		26,546	26,875
Accumulated depreciation	[1]	6,504	5,657
Property, plant and equipment, net		$ 20,042	$ 21,218
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]		Debt, Current	Debt, Current
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]		Long-term Debt and Lease Obligation	Long-term Debt and Lease Obligation
Finance Lease, Liability, Statement of Financial Position [Extensible Enumeration]		Debt, Current, Long-term Debt and Lease Obligation	Debt, Current, Long-term Debt and Lease Obligation
Finance Lease, Liability		$ 9
Third Party
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Liability, to be Paid, Year One		68
Lessee, Operating Lease, Liability, to be Paid, Year Two		59
Lessee, Operating Lease, Liability, to be Paid, Year Three		38
Lessee, Operating Lease, Liability, to be Paid, Year Four		21
Lessee, Operating Lease, Liability, to be Paid, Year Five		18
Lessee, Operating Lease, Liability, to be Paid, after Year Five		109
Lessee, Operating Lease, Liability, to be Paid		313
Operating Lease, Right-of-Use Asset		268	$ 309
Operating Lease, Liability, Current		59	63
Operating Lease, Cost		71	78	75
Finance Lease, Right-of-Use Asset, Amortization		2	3	5
Finance Lease, Interest Expense		1	1	1
Finance Lease Cost		3	4	6
Variable Lease, Cost		15	10	11
Short-term Lease, Cost		31	52	80
Lease, Cost		120	144	172
Operating Lease, Liability, Noncurrent		$ 205	$ 244
Operating Lease, Weighted Average Remaining Lease Term		8 years 3 months 18 days	8 years
Operating Lease, Weighted Average Discount Rate, Percent		4.10%	4.30%
Other current liabilities		$ 2	$ 2
Long-term debt		$ 7	$ 9
Finance Lease, Weighted Average Remaining Lease Term		19 years 4 months 24 days	16 years 10 months 24 days
Finance Lease, Weighted Average Discount Rate, Percent		6.00%	6.00%
Lessee, Operating Lease, Liability, Undiscounted Excess Amount		$ 49
Operating Lease, Liability		264	$ 307
Finance Lease, Liability		9	11
Marathon Petroleum Corporation [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Liability, to be Paid, Year One		15
Lessee, Operating Lease, Liability, to be Paid, Year Two		15
Lessee, Operating Lease, Liability, to be Paid, Year Three		14
Lessee, Operating Lease, Liability, to be Paid, Year Four		14
Lessee, Operating Lease, Liability, to be Paid, Year Five		14
Lessee, Operating Lease, Liability, to be Paid, after Year Five		575
Lessee, Operating Lease, Liability, to be Paid		647
Operating Lease, Right-of-Use Asset		229	231
Operating Lease, Liability, Current		1	1
Operating Lease, Liability, Noncurrent, Related Party		228	229
Operating Lease, Cost		15	14	14
Finance Lease, Right-of-Use Asset, Amortization		0	0	0
Finance Lease, Interest Expense		0	0	0
Finance Lease Cost		0	0	0
Variable Lease, Cost		0	1	1
Short-term Lease, Cost		0	0	0
Lease, Cost		$ 15	$ 15	$ 15
Operating Lease, Weighted Average Remaining Lease Term		45 years 2 months 12 days	46 years 2 months 12 days
Operating Lease, Weighted Average Discount Rate, Percent		5.80%	5.80%
Lessee, Operating Lease, Liability, Undiscounted Excess Amount		$ 418
Operating Lease, Liability		$ 229	$ 230
Lease Agreements, Lessee [Member] | Maximum
Lessee, Lease, Description [Line Items]
Term Of Agreements		57 years
Renewal Term Agreement		50 years
Lease Agreements, Lessee [Member] | Minimum
Lessee, Lease, Description [Line Items]
Term Of Agreements		1 year
Renewal Term Agreement		1 year
Finance Lease [Member] | Third Party
Lessee, Lease, Description [Line Items]
Property, plant and equipment, gross		$ 11	17
Accumulated depreciation		4	8
Property, plant and equipment, net		$ 7	$ 9
[1]	Includes property, plant and equipment impairment charges recorded during the respective period, as discussed below.

Leases Lessor Disclosures (Deta

Leases Lessor Disclosures (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Jun. 30, 2021	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Lessor, Lease, Description [Line Items]
Lessor, Sales-type Lease, Assumptions and Judgments, Value of Underlying Asset, Amount	$ 421	$ 171
Lessor, Operating Lease, Payment to be Received, Year One			$ 845
Sales-type Lease, Selling Profit (Loss)	112	209	0	$ 0	$ 21
Lessor, Operating Lease, Payment to be Received, Year Two			770
Lessor, Operating Lease, Payment to be Received, Year Three			718
Lessor, Operating Lease, Payment to be Received, Year Four			682
Lessor, Operating Lease, Payment to be Received, Year Five			646
Lessor, Operating Lease, Payment to be Received, after Year Five			1,607
Lessor, Operating Lease, Payments to be Received			5,268
Sales-type Lease, Lease Receivable	519	370
Sales-type Lease, Unguaranteed Residual Asset	$ 14	$ 10
Accumulated depreciation			2,042	2,007
Property, Plant and Equipment, Net			3,510	3,940
Property Subject to or Available for Operating Lease, Gross			5,552	5,947
Operating Lease, Lease Income, Related Party			743	952	1,196
Pipelines And Related Assets [Member]
Lessor, Lease, Description [Line Items]
Property Subject to or Available for Operating Lease, Gross			953	834
Refineries and related assets [Member]
Lessor, Lease, Description [Line Items]
Property Subject to or Available for Operating Lease, Gross			1,146	1,680
Terminals and related assets [Member]
Lessor, Lease, Description [Line Items]
Property Subject to or Available for Operating Lease, Gross			1,290	1,276
Barges and towing vessels [Member]
Lessor, Lease, Description [Line Items]
Property Subject to or Available for Operating Lease, Gross			129	129
Gas Gathering And Transmission Equipment And Facilities [Member]
Lessor, Lease, Description [Line Items]
Property Subject to or Available for Operating Lease, Gross			991	990
Processing, Fractionation And Storage Facilities [Member]
Lessor, Lease, Description [Line Items]
Property Subject to or Available for Operating Lease, Gross			867	867
Land Building Office Equipment And Other [Member]
Lessor, Lease, Description [Line Items]
Property Subject to or Available for Operating Lease, Gross			176	171
Third Party
Lessor, Lease, Description [Line Items]
Lessor, Operating Lease, Payment to be Received, Year One			213
Operating Lease, Lease Income			376	398	388
Sales-type Lease, Selling Profit (Loss)			0	0	0
Sales-type Lease, Interest Income			0	0	0
Sales-type Lease, Variable Lease Income			0	0	0
Lessor, Operating Lease, Payment to be Received, Year Two			207
Lessor, Operating Lease, Payment to be Received, Year Three			204
Lessor, Operating Lease, Payment to be Received, Year Four			171
Lessor, Operating Lease, Payment to be Received, Year Five			142
Lessor, Operating Lease, Payment to be Received, after Year Five			1,299
Lessor, Operating Lease, Payments to be Received			2,236
Sales-type Lease, Lease Receivable			1	1
Sales-type Lease, Revenue			0	0	0
Marathon Petroleum Corporation [Member]
Lessor, Lease, Description [Line Items]
Sales-Type and Direct Financing Leases, Lease Receivable, to be Received, Year One			544
Sales-Type and Direct Financing Leases, Lease Receivable, to be Received, Year Two			544
Sales-Type and Direct Financing Leases, Lease Receivable, to be Received, Year Three			538
Sales-Type and Direct Financing Leases, Lease Receivable, to be Received, Year Four			525
Sales-Type and Direct Financing Leases, Lease Receivable, to be Received, Year Five			422
Sales-Type and Direct Financing Leases, Lease Receivable, to be Received, after Year Five			595
Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received			3,168
Lessor, Operating Lease, Payment to be Received, Year One			632
Sales-type Lease, Selling Profit (Loss)			0	0	0
Sales-type Lease, Interest Income			431	151	6
Sales-type Lease, Variable Lease Income			4	1	1
Lessor, Operating Lease, Payment to be Received, Year Two			563
Lessor, Operating Lease, Payment to be Received, Year Three			514
Lessor, Operating Lease, Payment to be Received, Year Four			511
Lessor, Operating Lease, Payment to be Received, Year Five			504
Lessor, Operating Lease, Payment to be Received, after Year Five			308
Lessor, Operating Lease, Payments to be Received			3,032
Sales-type and Direct Financing Leases, Lease Receivable, Undiscounted Excess Amount			2,232
Sales-type Lease, Lease Receivable			936
Sales-type Lease, Unguaranteed Residual Asset			47	23
Sales-type Lease, Revenue			$ 435	$ 152	$ 7
Maximum | Lease Agreements, Lessor [Member]
Lessor, Lease, Description [Line Items]
Term Of Agreements			8 years
Renewal Term Agreement			5 years
Minimum | Lease Agreements, Lessor [Member]
Lessor, Lease, Description [Line Items]
Term Of Agreements			1 year
Renewal Term Agreement			1 year

Commitments and Contingencies_2

Commitments and Contingencies (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Commitments And Contingencies [Line Items]
Accrual for environmental loss contingencies	$ 23	$ 17
Receivable from MPC for indemnification of environmental costs	644	677
Contractual commitments to acquire property, plant and equipment	116
Loss Contingency, Damages Sought, Value		187
Loss Contingency, Damages Paid, Value		4
Environmental Loss Contingency [Member] | Marathon Petroleum Corporation [Member]
Commitments And Contingencies [Line Items]
Receivable from MPC for indemnification of environmental costs	0	$ 0
Guarantee Type, Other [Member]
Commitments And Contingencies [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 230
Minimum | Minimum Committed Volume Contracts [Member]
Commitments And Contingencies [Line Items]
Term Of Agreements	1 year

Commitments and Contingencies_3

Commitments and Contingencies (Minimum Future Payments) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)
Transportation And Terminalling Agreements
Other Commitments [Line Items]
2020	$ 117
2021	155
2022	146
2023	124
2024	111
2025 and thereafter	310
Total	$ 963
Minimum Committed Volume Contracts [Member] | Minimum
Other Commitments [Line Items]
Term Of Agreements	1 year
Minimum Committed Volume Contracts [Member] | Maximum
Other Commitments [Line Items]
Term Of Agreements	10 years