Accounting Policies [Abstract] Business Description and Basis of Presentation [Text Block] Business Description and Basis of Presentation [Text Block] Income Tax Disclosure [Abstract] Current income tax expense: Current Income Tax Expense (Benefit), Continuing Operations [Abstract] Federal Current Federal Tax Expense (Benefit) State Current State and Local Tax Expense (Benefit) Total current Current Income Tax Expense (Benefit) Deferred income tax expense (benefit): Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract] Federal Deferred Federal Income Tax Expense (Benefit) State Deferred State and Local Income Tax Expense (Benefit) Total deferred Deferred Income Tax Expense (Benefit) Provision (benefit) for income tax Income Tax Expense (Benefit) Quarterly Financial Information Disclosure [Abstract] Quarterly Financial Data [Table] Quarterly Financial Data [Table] Quarterly Financial Data [Table] Related Party [Axis] Related Party [Axis] Related Party [Domain] Related Party [Domain] MPC Marathon Petroleum Corporation [Member] Marathon petroleum corporation. Non Related Party [Axis] Non Related Party [Axis] Non Related Party [Axis] Non Related Party [Domain] Non Related Party [Domain] Non Related Party [Domain] Public Public [Member] Public [Member] Investment, Name [Axis] Investment, Name [Axis] Investment, Name [Domain] Investment, Name [Domain] Ohio Condensate Ohio Condensate Company, LLC [Member] Ohio Condensate Company, LLC [Member] Partner Type [Axis] Partner Type [Axis] Partner Type of Partners' Capital Account, Name [Domain] Partner Type of Partners' Capital Account, Name [Domain] Limited Partners Common Units Limited Partners Common Units [Member] Limited Partners Common Units [Member] Limited Partners Subordinated Units Limited Partners Subordinated Units [Member] Limited Partners Subordinated Units [Member] Limited Partner GP Units GP Held Limited Partners Common Units [Member] GP Held Limited Partners Common Units [Member] Redeemable Preferred Units Preferred Partner [Member] Quarterly Financial Data [Line Items] Quarterly Financial Data [Line Items] Quarterly Financial Data [Line Items] Total revenues and other income Revenues Income from operations Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent Net income (loss) Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Net income (loss) attributable to MPLX LP Net Income (Loss) Attributable to Parent Net income (loss) attributable to MPLX LP per limited partner unit: Net Income Attributable To Parent Company Per Limited Partner Unit Basic And Diluted [Abstract] Net Income Attributable To Parent Company Per Limited Partner Unit Basic And Diluted [Abstract] Common - basic (in USD per unit) Net Income (Loss), Per Outstanding Limited Partnership Unit, Basic, Net of Tax Common - diluted (in USD per unit) Net Income (Loss), Net of Tax, Per Outstanding Limited Partnership Unit, Diluted Subordinated - basic and diluted (in USD per unit) Net Income (Loss), Per Outstanding Limited Partnership and General Partnership Unit, Basic and Diluted, Net of Tax Cash distributions declared per limited partner common unit Distribution Made to Limited Partner, Distributions Declared, Per Unit Distributions declared: Distributions declared: [Abstract] Distributions declared: [Abstract] Total cash distributions declared Distribution Made to Limited Partner, Cash Distributions Declared Distribution declared, general partner Distribution Made to General Partner, Cash Distribution Declared Amount of equity impact of cash distribution declared to general partner of limited partnership (LP). Incentive distribution, subsequent distribution amount Incentive Distribution, Subsequent Distribution Amount Amount of incentive obligation earned in cash or stock during the period by a limited partnership general partner and paid after the end of the accounting period. Total distributions declared Distributions Made to Partners, Total Cash Distribution Declared The amount of cash distributions declared to partners by a limited partnership. Impairment expense Goodwill and Intangible Asset Impairment Impairment related to equity method investment from asset impairment and elimination of basis differential Income (Loss) from Equity Method Investments from Asset Impairment and Elimination of Basis Differential Income (Loss) from Equity Method Investments from Asset Impairment and Elimination of Basis Differential Related Party Transactions [Abstract] Schedule of Related Party Transactions, by Related Party [Table] Schedule of Related Party Transactions, by Related Party [Table] MarkWest Utica EMG MarkWest Utica EMG [Member] MarkWest Utica EMG [Member] Ohio Gathering Ohio Gathering Company, LLC [Member] Ohio Gathering Company, LLC [Member] Jefferson Dry Gas MarkWest EMG Jefferson Dry Gas Gathering Company, L.L.C. [Member] MarkWest EMG Jefferson Dry Gas Gathering Company, L.L.C. [Member] Sherwood Midstream Sherwood Midstream [Member] Sherwood Midstream [Member] Other Other Affiliates [Member] Related Party Transaction [Line Items] Related Party Transaction [Line Items] Other income - related parties Related Party Transaction, Other Revenues from Transactions with Related Party Commitments and Contingencies Disclosure [Abstract] Recorded Unconditional Purchase Obligation [Table] Recorded Unconditional Purchase Obligation [Table] Recorded Unconditional Purchase Obligation by Category of Item Purchased [Axis] Recorded Unconditional Purchase Obligation by Category of Item Purchased [Axis] Unconditional Purchase Obligation, Category of Goods or Services Acquired [Domain] Unconditional Purchase Obligation, Category of Goods or Services Acquired [Domain] SMR Transaction Smr Product [Member] The entire product produced by a steam methane reformer to be received in exchange for payments of processing fees and the reimbursement of other expenses. Recorded Unconditional Purchase Obligation [Line Items] Recorded Unconditional Purchase Obligation [Line Items] 2018 Recorded Unconditional Purchase Obligation Due in Next Twelve Months 2019 Recorded Unconditional Purchase Obligation Due in Second Year 2020 Recorded Unconditional Purchase Obligation Due in Third Year 2021 Recorded Unconditional Purchase Obligation Due in Fourth Year 2022 Recorded Unconditional Purchase Obligation Due in Fifth Year 2023 and thereafter Recorded Unconditional Purchase Obligation Due after Fifth Year Total minimum payments Recorded Unconditional Purchase Obligation Less: Services element Product Supply Agreement Future Minimum Payments Services Included in Payment The portion of the total contractually required payments under the product supply agreement that relates to fees for services. Less: Interest Product Supply Agreements Future Minimum Payments Interest Included in Payments The portion of the total contractually required payments under the product supply agreement that relates to interest expense. Total SMR liability Steam Methane Reformer Liability Aggregate carrying amount, as of the balance sheet date, of the liability associated with the sale of an SMR accounted for as a financing arrangement. Less: Current portion of SMR liability Steam Methane Reformer Liability Current Aggregate carrying amount, as of the balance sheet date, of the current portion of the liability associated with the sale of an SMR accounted for as a financing arrangement. Current liabilities are expected to be paid within one year (or the normal operating cycle, if longer). Long-term portion of SMR liability Steam Methane Reformer Liability Noncurrent Aggregate carrying amount, as of the balance sheet date, of the noncurrent portion of the liability associated with the sale of an SMR accounted for as a financing arrangement. Noncurrent liabilities are expected to be paid after one year (or the normal operating cycle, if longer). Service revenue - related parties Sales Revenue, Services from Related Parties Aggregate revenue revenue from related parties during the period from services rendered in the normal course of business. Rental income - related parties Operating Lease, Income Statement, Lease Revenue, Related Parties The total amount of revenue recognized for the period from operating leases, including minimum lease revenue, contingent revenue, percentage revenue and sublease revenue from related parties. Product sales - related parties Sales Revenue, Goods, Related Parties Aggregate revenue from related parties from the sale of goods in the normal course of business. Sales revenue, goods, related party, net zero Sales Revenue, Goods, Related Party, Net Zero Revenue from related parties from the sale of goods in the normal course of business that net zero on the financial statements due to the terms of the contract. Sherwood Midstream LLC Sherwood Midstream LLC [Member] Sherwood Midstream LLC Sherwood Midstream Holdings Sherwood Midstream Holdings [Member] Sherwood Midstream Holdings [Member] Type of Arrangement and Non-arrangement Transactions [Axis] Type of Arrangement and Non-arrangement Transactions [Axis] Arrangements and Non-arrangement Transactions [Domain] Arrangements and Non-arrangement Transactions [Domain] Commercial Agreements Commercial Agreements [Member] Commercial Agreements [Member] Operating Agreements Operating Agreements [Member] Operating Agreements [Member] Management Services Agreements Management Services Agreements [Member] Management Services Agreements [Member] MPC Investment MPC Investment [Member] MPC Investment [Member] MPL Investment LLC MPL Investment LLC [Member] MPL Investment LLC [Member] Parties to Contractual Arrangement [Axis] Lease Arrangement, Type [Axis] Parties to Contractual Arrangement [Domain] Lease Arrangement, Type [Domain] Transportation Services Agreements [Member] Transportation Services Agreements [Member] Transportation Services Agreements [Member] Five Year Transportation Services Agreement [Member] Five Year Transportation Services Agreement [Member] Five Year Transportation Services Agreement [Member] Six Year Transportation Services Agreement [Member] Six Year Transportation Services Agreement [Member] Six Year Transportation Services Agreement [Member] Ten Year Storage Services Agreement [Member] Ten Year Storage Services Agreement [Member] Ten Year Storage Services Agreement [Member] Seventeen Year Storage Services Agreement [Member] Seventeen Year Storage Services Agreement [Member] Seventeen Year Storage Services Agreement [Member] Three Year Storage Services Agreement [Member] Three Year Storage Services Agreement [Member] Three Year Storage Services Agreement [Member] Storage Services Agreements Storage Services Agreements [Member] Storage Services Agreements [Member] Ten Year Terminal Services Agreement [Member] Ten Year Terminal Services Agreement [Member] Ten Year Terminal Services Agreement [Member] Terminal Services Agreements Terminal Services Agreements [Member] Terminal Services Agreements [Member] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum Minimum [Member] Maximum Maximum [Member] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Related Party Revolving Credit Agreement Related Party Revolving Credit Agreement [Member] Related Party Revolving Credit Agreement [Member] Products and Services [Axis] Products and Services [Axis] Products and Services [Domain] Products and Services [Domain] Handling crude oil and products Handling Crude Oil And Products [Member] Handling Crude Oil And Products [Member] Providing marine transportation of crude oil, feedstocks and refined petroleum products, and related services Providing marine transportation of crude oil, feedstocks and refined petroleum products, and related services [Member] Providing marine transportation of crude oil, feedstocks and refined petroleum products, and related services [Member] Storage services tank farms Storage Services Tank Farm [Member] Storage Services Tank Farm [Member] Crude oil and product pipeline Crude Oil And Product Pipeline [Member] Crude Oil And Product Pipeline [Member] Refined products Refined Products [Member] Refined Products [Member] Terminal storage and related services Terminal storage and related services [Member] Terminal storage and related services [Member] Equity method investment, ownership percentage Equity Method Investment, Ownership Percentage Commercial Agreements Commercial Agreements [Abstract] Commercial Agreements [Abstract] Renewal term agreement Renewal Term Agreement Renewal Term Agreement Duration of agreements (in years) Term Of Agreements Term Of Agreements Automatic renewal term agreement Automatic Renewal Term Agreement Automatic Renewal Term Agreement Number of renewals Number of Renewals Number of Times for Automatic Renewal Loan Agreement [Abstract] Loan Agreement [Abstract] Loan Agreement [Abstract] Initiation date Line of Credit Facility, Initiation Date Current borrowing capacity Line of Credit Facility, Current Borrowing Capacity Expiration date Line of Credit Facility, Expiration Date Description of variable rate basis Debt Instrument, Description of Variable Rate Basis Proceeds from lines of credit Proceeds from Lines of Credit Repayments of lines of credit Repayments of Lines of Credit Outstanding balance Long-term Line of Credit Interest rate during period Line of Credit Facility, Interest Rate During Period Prepaid insurance Prepaid Insurance Revenue from related parties Revenue from Related Parties Purchases from related parties Related Party Transaction, Purchases from Related Party Earnings Per Share [Abstract] Schedule Of Earnings Per Share Basic And Diluted [Table] Schedule Of Earnings Per Share Basic And Diluted [Table] Schedule Of Earnings Per Share Basic And Diluted [Table] General Partner General Partner [Member] Preferred Units Schedule Of Earnings Per Share Basic And Diluted [Line Items] Schedule Of Earnings Per Share Basic And Diluted [Line Items] Schedule Of Earnings Per Share Basic And Diluted [Line Items] Net income attributable to MPLX LP: Partnership Income [Abstract] Undistributed net income loss attributable to MPLX LP Undistributed Earnings (Loss) Available to Common Shareholders, Basic Net income attributable to MPLX LP Weighted average units outstanding: Net Income (Loss), Per Outstanding Limited Partnership Unit, Basic, Other Disclosures [Abstract] Basic (shares) Weighted Average Limited Partnership Units Outstanding, Basic Diluted (shares) Weighted Average Limited Partnership Units Outstanding, Diluted Net income attributable to MPLX LP subsequent to initial public offering per limited partner unit: Net Income Loss Per Outstanding Limited Partnership Unit Basic And Diluted [Abstract] Net Income Loss Per Outstanding Limited Partnership Unit Basic And Diluted [Abstract] Basic (in USD per unit) Diluted (in USD per unit) Derivative Instruments and Hedging Activities Disclosure [Abstract] Derivative Financial Instruments Derivative Instruments and Hedging Activities Disclosure [Text Block] Equity [Abstract] Distributions to preferred unitholders Dividends, Preferred Stock General partner's IDRs and other Incentive Distribution Rights And Other Amount of incentive distribution rights earned in cash or stock during the period by a limited partnership general partner, as well as other items to be deducted from net income before calculating the general partner's two percent interest. Net income attributable to MPLX LP available to general and limited partners Net Income (Loss) Available To General And Limited Partners Net income after adjustments for Incentive Distribution Rights of the general partner. General partner's two percent GP Interest in net income attributable to MPLX LP Net Income (Loss) Allocated To General Partner, Excluding Incentive Distribution Amount of net income allocated to the general partner, excluding incentive distribution rights. General partner's GP Interest in net income attributable to MPLX LP Net Income (Loss) Allocated to General Partners Segment Reporting [Abstract] Reconciliation of Other Significant Reconciling Items from Segments to Consolidated [Table] Reconciliation of Other Significant Reconciling Items from Segments to Consolidated [Table] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Operating Segments Operating Segments [Member] Segment Reconciling Items Segment Reconciling Items [Member] Segments [Axis] Segments [Axis] Segments [Domain] Segments [Domain] L&S Logistics and Storage [Member] Logistics and Storage [Member] G&P Gathering and Processing [Member] Gathering and Processing [Member] Segment Reporting, Other Significant Reconciling Item [Line Items] Segment Reporting, Other Significant Reconciling Item [Line Items] Capital expenditures Payments to Acquire Property, Plant, and Equipment Fair Value Disclosures [Abstract] Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement [Member] Portion at Fair Value Measurement [Member] Estimate of Fair Value Measurement [Member] Estimate of Fair Value Measurement [Member] Reported Value Measurement [Member] Reported Value Measurement [Member] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Long-term debt Long-term Debt, Fair Value SMR liability Other Liabilities, Fair Value Disclosure Income Tax Income Tax Disclosure [Text Block] Debt Disclosure [Abstract] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Cash and Cash Equivalents [Member] Cash and Cash Equivalents [Member] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] MPLX LP MPLX LP [Member] MPLX LP [Member] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] HST & WHC & MPLXT HST & WHC & MPLXT [Member] HST & WHC & MPLXT [Member] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Senior Notes Senior Notes [Member] 4.125% senior notes due March 2027 Senior Notes Due March 2027 [Member] Senior Notes Due March 2027 [Member] 5.200% senior notes due March 2047 Senior Notes Due March 2047 [Member] Senior Notes Due March 2047 [Member] Debt Instrument [Line Items] Debt Instrument [Line Items] Long-term debt, gross Long-term Debt, Gross Interest rate, stated percentage Debt Instrument, Interest Rate, Stated Percentage Percent of par Percent of Par Percent of Par Payments to acquire businesses, gross Payments to Acquire Businesses, Gross Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Purchases - related parties Purchases From Related Parties [Member] Purchases From Related Parties [Member] General and administrative expenses General and Administrative Expense [Member] Expenses incurred under employee services agreements Labor and Related Expense Reconciliation of Revenue from Segments to Consolidated [Table] Reconciliation of Revenue from Segments to Consolidated [Table] Segment Reporting, Revenue Reconciling Item [Line Items] Segment Reporting, Revenue Reconciling Item [Line Items] Reconciliation to Total revenues and other income: Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract] Revenue adjustment for unconsolidated affiliates Revenue adjustment for unconsolidated affiliates Revenue adjustment for unconsolidated affiliates Income (loss) from equity method investments Income (Loss) from Equity Method Investments Unrealized derivative gains (losses) related to product sales Derivative, Loss on Derivative Business Combinations [Abstract] Acquisitions Business Combination Disclosure [Text Block] Leases [Abstract] Operating lease revenue, excluding executory costs Operating lease revenue, excluding executory costs Operating lease revenue, excluding executory costs Operating leases of lessor contingent rentals received Operating Leases of Lessor Contingent Rentals Received Represents the contingent lease payments received under the contingent rental provisions. Restricted cash Restricted Cash and Cash Equivalents, Current Threshold relocation cost of assets as percentage of fair value to be classified as real estate Threshold Relocation Cost of Assets as Percentage of Fair Value to be Classified as Real Estate Represents the minimum threshold for relocation costs of tangible assets, expressed as a percentage of the fair value of the asset, that will result in the asset being classified as "in-substance" real estate. Impairment losses Goodwill, Impairment Loss Supplemental Cash Flow Elements [Abstract] Summary of Supplemental Cash Flow Information Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Summary of Changes in Capital Accruals Schedule Of Reconciliation Of Additions To Property Plant And Equipment To Total Capital Expenditures [Table Text Block] Schedule of Reconciliation of Additions to Property, Plant And Equipment to Total Capital Expenditures [Table Text Block] Long-term receivables - related parties Due from Related Parties, Noncurrent Goodwill and Intangible Assets Disclosure [Abstract] Goodwill and Intangibles Goodwill and Intangible Assets Disclosure [Text Block] Income Statement [Abstract] Statement [Table] Statement [Table] Statement [Line Items] Statement [Line Items] Revenues and other income: Revenues And Other Income [Abstract] Revenues and Other Income [Abstract] Service revenue Sales Revenue, Services, Net Rental income Operating Leases, Income Statement, Lease Revenue Product sales Sales Revenue, Goods, Net Gain on sale of assets Gain (Loss) on Disposition of Assets for Financial Service Operations Other income Other Operating Income Other income - related parties Total segment revenues and other income Costs and expenses: Costs and Expenses [Abstract] Cost of revenues (excludes items below) Refining and Marketing Costs Purchased product costs Natural Gas Midstream Costs Rental cost of sales Cost of Rental Sales and Occupancy Costs Cost of Rental Sales and Occupancy Costs Rental cost of sales - related parties Cost of Rental Sales and Occupancy Costs, Related Parties Cost of Rental Sales and Occupancy Costs, Related Parties Purchases - related parties Costs and Expenses, Related Party Depreciation and amortization Depreciation Impairment expense General and administrative expenses General and Administrative Expense Other taxes Taxes, Miscellaneous Total costs and expenses Costs and Expenses Income from operations Related party interest and other financial costs Interest And Other Financial Costs From Related Parties Interest And Other Financial Costs From Related Parties Interest expense (net of amounts capitalized of $32 million, $28 million, $5 million, respectively) Interest Expense, Debt, Excluding Amortization Other financial costs Other Nonoperating Income (Expense) Income before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Provision (benefit) for income taxes Net income Less: Net income attributable to noncontrolling interests Net Income (Loss) Attributable to Noncontrolling Interest Less: Net income attributable to Predecessor Income (Loss) Attributable to Predecessor Income (Loss) Attributable to Predecessor Net income attributable to MPLX LP Less: Preferred unit distributions Less: General partner’s interest in net income attributable to MPLX LP Limited partners’ interest in net income attributable to MPLX LP Net Income (Loss) Allocated to Limited Partners Per Unit Data (See Note 7) Net Income (Loss), Per Outstanding Limited Partnership Unit, Basic, Net of Tax [Abstract] Net income attributable to MPLX LP per limited partner unit: Weighted average limited partner units outstanding: Limited Partners' Capital Account [Abstract] Common - basic (in units) Common - diluted (in units) Subordinated - basic and diluted (in units) Weighted Average Number of Limited Partnership and General Partnership Unit Outstanding, Basic and Diluted Redeemable Preferred Units Disclosure [Abstract] Redeemable Preferred Units Disclosure [Abstract] Redeemable Noncontrolling Interest, by Legal Entity [Table] Redeemable Noncontrolling Interest, by Legal Entity [Table] Preferred Units by Name [Axis] Preferred Units by Name [Axis] Preferred Units, Class [Domain] Preferred Units, Class [Domain] Series A Convertible Preferred Units Series A Convertible Preferred Units [Member] Series A Convertible Preferred Units [Member] Redeemable Noncontrolling Interest [Line Items] Redeemable Noncontrolling Interest [Line Items] Issuance of preferred units Partners' Capital Account, Units, Sale of Units Preferred units, dividend rate, percentage Preferred Stock, Dividend Rate, Percentage Units issued, price per unit Shares Issued, Price Per Share Issuance of redeemable preferred units Proceeds from Issuance of Preferred Limited Partners Units Preferred units, dividend rate, per-dollar-amount Preferred Stock, Dividend Rate, Per-Dollar-Amount Distributions to preferred units Preferred units, description Preferred Units, Description Derivative [Table] Derivative [Table] Product sales Product Sales [Member] Product Sales [Member] Purchased product costs Purchased product costs [Member] Purchased product costs [Member] Cost of revenues Cost of Sales [Member] Derivative Instruments, Gain (Loss) [Line Items] Derivative Instruments, Gain (Loss) [Line Items] Realized (loss) gain Derivative Instruments Not Designated as Hedging Instruments, Realized Gain (Loss), Net Amount of realized gain (loss) of derivative instruments not designated or qualifying as hedging instruments. Unrealized gain (loss) Derivative Instruments Not Designated as Hedging Instruments, Unrealized Gain (Loss), Net Amount of unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments. Total derivative loss Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net Summary of Quarterly Financial Data Quarterly Financial Information [Table Text Block] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] MarkWest MarkWest [Member] MarkWest [Member] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Number of reportable segments Number of Reportable Segments Effective date of acquisition Business Acquisition, Effective Date of Acquisition Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Equity Transactions And Share Based Compensation [Table] Equity Transactions And Share Based Compensation [Table] Equity Transactions And Share Based Compensation [Table] Title of Individual [Axis] Title of Individual [Axis] Relationship to Entity [Domain] Relationship to Entity [Domain] Officer Officer [Member] Plan Name [Axis] Plan Name [Axis] Plan Name [Domain] Plan Name [Domain] Mplx 2012 Incentive Compensation Plan [Member] Mplx Two Thousand Twelve Incentive Compensation Plan [Member] Mplx two thousand twelve incentive compensation plan. Award Type [Axis] Award Type [Axis] Equity Award [Domain] Equity Award [Domain] Phantom Units Phantom Share Units (PSUs) [Member] Performance Shares Performance Shares [Member] Equity-Based Compensation [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Description of the Plan Equity-Based Compensation Plan, Description [Abstract] Equity-Based Compensation Plan, Description [Abstract] Common units available for delivery under the plan Stock or Units Available for Distributions Unit-based awards under the Plan Equity-Based Compensation Plan, Unit-Based Awards [Abstract] Equity-Based Compensation Plan, Unit-Based Awards [Abstract] Award requisite service period Share-based Compensation Arrangement by Share-based Payment Award, Award Requisite Service Period Accrued distributions Deferred Compensation Share-based Arrangements, Liability, Current and Noncurrent Measurement period Measurement Periods Measurement Periods Award percentage paid out in cash Share Based Compensation Arrangement By Share Based Payment Award Percentage Paid Out In Cash Share Based Compensation Arrangement By Share Based Payment Award Percentage Paid Out In Cash Award percentage paid out in stock Share Based Compensation Arrangement By Share Based Payment Award Percentage Paid Out In Stock Share Based Compensation Arrangement By Share Based Payment Award Percentage Paid Out In Stock Grant date fair value of performance units granted Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Outstanding Phantom and Performance Unit Awards Equity-Based Compensation Plan, Outstanding Phantom Unit Awards [Abstract] Equity-Based Compensation Plan, Outstanding Phantom Unit Awards [Abstract] Convertible at December 31, 2017 Share Based Compensation Arrangement By Share Based Payment Award Non Options Convertible Convertible units as of the balance sheet date. Unrecognized compensation cost Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options Cost not yet recognized, period for recognition Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Vested and expected to vest at December 31, 2017 Share Based Compensation Arrangement By Share Based Payment Award Non Options Vested And Expected To Vest Outstanding Number The number of vested and expected to vest shares as of the balance sheet date. Compensation Expense Share-based Compensation [Abstract] Total compensation expense Allocated Share-based Compensation Expense Stock-based compensation plans expenses Share-based Compensation Other Commitments [Table] Other Commitments [Table] Other Commitments [Axis] Other Commitments [Axis] Other Commitments [Domain] Other Commitments [Domain] Transportation And Terminalling Agreements Operating Leases Propane Storage And Transporation And Terminalling Agreements [Member] Represents various non-cancellable operating lease agreements, a long-term propane storage agreement, and transportation and terminalling agreements. Other Commitments [Line Items] Other Commitments [Line Items] 2018 Contractual Obligation, Due in Next Fiscal Year 2019 Contractual Obligation, Due in Second Year 2020 Contractual Obligation, Due in Third Year 2021 Contractual Obligation, Due in Fourth Year 2022 Contractual Obligation, Due in Fifth Year 2023 and thereafter Contractual Obligation, Due after Fifth Year Total Contractual Obligation Equity-Based Compensation Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Use of estimates Use of Estimates, Policy [Policy Text Block] Revenue recognition Revenue Recognition, Policy [Policy Text Block] Revenue and expense accruals Revenue and Expense Accruals Policy [Policy Text Block] Disclosure of the accounting policy for revenue and expense accruals. Cash and cash equivalents Cash and Cash Equivalents, Policy [Policy Text Block] Restricted cash Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block] Receivables Trade and Other Accounts Receivable, Policy [Policy Text Block] Inventories Inventory, Policy [Policy Text Block] Imbalances Product Imbalances Policy [Text Block] Product Imbalances [Policy Text Block] Property, plant and equipment Property, Plant and Equipment, Policy [Policy Text Block] Intangibles Goodwill and Intangible Assets, Intangible Assets, Policy [Policy Text Block] Goodwill Goodwill and Intangible Assets, Goodwill, Policy [Policy Text Block] Other taxes Taxes Other Than Income Taxes Policy [Text Block] Taxes Other Than Income Taxes Policy [Text Block] Environmental costs Environmental Costs, Policy [Policy Text Block] Asset retirement obligations Asset Retirement Obligation [Policy Text Block] Investment in unconsolidated affiliates Equity Method Investments [Policy Text Block] Deferred financing costs Debt, Policy [Policy Text Block] Derivative instruments Derivatives, Policy [Policy Text Block] Fair value of financial instruments Fair Value of Financial Instruments, Policy [Policy Text Block] Fair value measurement Fair Value Measurement, Policy [Policy Text Block] Equity-based compensation arrangements Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block] Tax effects of share-based compensation Tax Effect of Share based Compensation [Policy Text Block] Disclosure of accounting policy for income tax effects of share-based compensation. Income taxes Income Tax, Policy [Policy Text Block] Distributions Incentive Distribution Policy, Managing Member or General Partner, Description [Policy Text Block] Net income per limited partner unit Earnings Per Share, Policy [Policy Text Block] Business combinations Business Combinations Policy [Policy Text Block] Accounting for changes in ownership interests in subsidiaries Accounting for Changes in Ownership Interests in Subsidiaries [Policy Text Block] Disclosure of accounting policy for change in ownership interest in subsidiaries that includes method of accounting used for different circumstances under which there is a change in ownership interest in subsidiaries. Description Of Business And Basis Of Presentation [Table] Description Of Business And Basis Of Presentation [Table] Description Of Business And Basis Of Presentation [Table] Illinois Extension Illinois Extension Pipeline Company LLC [Member] Illinois Extension Pipeline Company LLC [Member] LOOP Loop Llc [Member] LOOP LLC [Member] LOCAP Locap Llc [Member] Locap Llc [Member] Explorer Explorer Pipeline [Member] Explorer Pipeline [Member] Hardin Street Marine Hardin Street Marine [Member] Hardin Street Marine [Member] LOOP LOCAP SAX and Explorer LOOP LOCAP SAX and Explorer Llc [Member] LOOP LOCAP SAX and Explorer Llc [Member] Description Of Business And Basis Of Presentation [Line Items] Description Of Business And Basis Of Presentation [Line Items] Description Of Business And Basis Of Presentation [Line Items] Date of partnership formation Limited Liability Company or Limited Partnership, Business, Formation Date Date for initial public offering completed Initial Public Offering Completion Date Initial Public Offering Completion Date Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] Commodity contracts Commodity Contract [Member] Hedging Designation [Axis] Hedging Designation [Axis] Hedging Designation [Domain] Hedging Designation [Domain] Not Designated as Hedging Instrument Not Designated as Hedging Instrument [Member] Other current assets Other Current Assets [Member] Other current liabilities Other Current Liabilities [Member] Other noncurrent assets Other Noncurrent Assets [Member] Deferred credits and other liabilities Other Noncurrent Liabilities [Member] Derivatives, Fair Value [Line Items] Derivatives, Fair Value [Line Items] Derivative asset, fair value, gross asset Derivative Asset, Fair Value, Gross Asset Derivative liability, fair value, gross liability Derivative Liability, Fair Value, Gross Liability Equity Method Investments and Joint Ventures [Abstract] Schedule of Equity Method Investments [Table] Schedule of Equity Method Investments [Table] Other VIEs Other VIEs [Member] Other VIEs [Member] Non-VIEs Non-VIEs [Member] Non-VIEs [Member] Schedule of Equity Method Investments [Line Items] Schedule of Equity Method Investments [Line Items] Revenue and other income Equity Method Investment, Summarized Financial Information, Revenue Costs and expenses Equity Method Investment, Summarized Financial Information, Costs and Expenses Equity Method Investment, Summarized Financial Information, Costs and Expenses Income (loss) from operations Equity Method Investment, Summarized Financial Information, Income (Loss) from Continuing Operations Net income (loss) Equity Method Investment, Summarized Financial Information, Net Income (Loss) Current assets Equity Method Investment, Summarized Financial Information, Current Assets Noncurrent assets Equity Method Investment, Summarized Financial Information, Noncurrent Assets Current liabilities Equity Method Investment, Summarized Financial Information, Current Liabilities Noncurrent liabilities Equity Method Investment, Summarized Financial Information, Noncurrent Liabilities Investment in subsidiary Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures Basis difference Equity Method Investment, Difference Between Carrying Amount and Underlying Equity Basis difference, not amortized Equity Method Investment Difference Between Carrying Amount And Underlying Equity Portion Related To Goodwill and Other Assets Not Amortized Equity method investment difference between carrying amount and underlying equity, portion related to goodwill and other assets which is not being amortized Income Taxes [Table] Income Taxes [Table] Income Taxes [Table] Income Tax Authority [Axis] Income Tax Authority [Axis] Income Tax Authority [Domain] Income Tax Authority [Domain] Federal Federal [Member] Federal [Member] State State [Member] State [Member] Income Taxes [Line Items] Income Taxes [Line Items] Income Taxes [Line Items] Deferred tax liabilities assumed Deferred tax liabilities assumed by parent Deferred tax liabilities assumed by parent in conjunction with Class A Reorganization Income tax rate Effective Income Tax Rate Reconciliation, Percent Federal statutory rate Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Deferred tax liabilities, net Deferred Tax Liabilities, Net Net penalties and interest expense (benefits) Unrecognized Tax Benefits Income Tax Net Penalties and Interest Expense (Benefits) Unrecognized Tax Benefits Income Tax Net Penalties and Interest Expense (Benefits) Penalties and interest accrued Income Tax Examination, Penalties and Interest Accrued Open tax year Open Tax Year Increase (decrease) in capital accruals Increase Decrease In Capital Accruals Increase (Decrease) In Capital Accruals Schedule of Restructuring and Related Costs [Table] Schedule of Restructuring and Related Costs [Table] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Domain] Property, Plant and Equipment, Type [Domain] Construction-in-progress Asset under Construction [Member] Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Costs added to property, plant and equipment Property, Plant and Equipment, Additions Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Charges for services received under the omnibus agreement Related Party Transaction, Expenses from Transactions with Related Party Asset Retirement Obligation Disclosure [Abstract] Reconciliation of Changes in Asset Retirement Obligations [Table Text Block] Schedule of Change in Asset Retirement Obligation [Table Text Block] Income from operations and capital expenditures by segment [Table Text Block] Schedule of Segment Reporting Information, by Segment [Table Text Block] Reconciliation to Income from Operations [Table Text Block] Reconciliation of Operating Profit (Loss) from Segments to Consolidated [Table Text Block] Reconciliation to Total Revenues and other income [Table Text Block] Reconciliation of Revenue from Segments to Consolidated [Table Text Block] Reconciliation of Net Income Attributable to Noncontrolling Interests [Table Text Block] Reconciliation of Net Income Attributable to Noncontrolling Interests and Predecessor [Table Text Block] Reconciliation of Net Income Attributable to Noncontrolling Interests and Predecessor [Table Text Block] Reconciliation of Other Significant Reconciling Items from Segments to Consolidated [Table Text Block] Reconciliation of Other Significant Reconciling Items from Segments to Consolidated [Table Text Block] Reconciliation of Assets from Segment to Consolidated [Table Text Block] Reconciliation of Assets from Segment to Consolidated [Table Text Block] Segment revenues Segment other income Segment cost of revenues Cost of Revenue Segment operating income before portion attributable to noncontrolling interests and Predecessor Segment operating income Segment operating income including the portion attributable to the noncontrolling interest Segment portion attributable to noncontrolling interests and Predecessor Minority Interest and Predecessor Interest in Operating Income (Loss) Limited Partnerships Amount of operating income or loss attributable to the reportable segments for the period that is attributable to the non-controlling partners of the entity's less than wholly-owned subsidiaries and the Predecessor entity. Segment operating income attributable to MPLX LP Segment operating income attributable to parent Segment operating income attributable to parent Inventory Disclosure [Abstract] NGLs Energy Related Inventory, Natural Gas Liquids Line fill Natural Gas or Natural Gas Liquids in Storage Carrying amount as of the balance sheet date of natural gas or natural gas liquids in storage, which is ready for sale. Spare parts, materials and supplies Other Inventories, Spare Parts, Gross Total inventories Inventory, Gross Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Reconciliation to Income from operations: Segment Reconciliation [Abstract] Segment operating income attributable to MPLX LP Segment portion attributable to unconsolidated affiliates Portion of segment operating income attributable to unconsolidated affiliates Portion of segment operating income attributable to unconsolidated affiliates Segment portion attributable to Predecessor Unrealized derivative (losses) gains Derivative, Gain on Derivative Depreciation and amortization Impairment expense General and administrative expenses Revenue from Related Parties Schedule of Entity Wide Information Sales to Related Parties [Table Text Block] Schedule of Entity Wide Information Sales to Related Parties [Table Text Block] Summary of Fees Received for Operating Pipelines for Related Parties Included in Other Income - Related Parties Schedule of Entity Wide Information Fees Received From Related Parties Included in Other Income [Table Text Block] Schedule of Entity Wide Information Fees Received From Related Parties Included in Other Income [Table Text Block] Schedule of Entity Wide Information Allocated Related Party Omnibus Agreement Costs by Income Stmt Line Schedule of Entity Wide Information Allocated Related Party Omnibus Agreement Costs by Income Stmt Line [Table Text Block] Schedule of Entity Wide Information Allocated Related Party Omnibus Agreement Costs by Income Statement Line [Table Text Block] Summary of Related Party Costs Added to Property, Plant and Equipment Schedule of Entity Wide Information Related Party Costs Added to Property Plant and Equipment [Table Text Block] Schedule of Entity Wide Information Related Party Costs Added to Property Plant and Equipment [Table Text Block] Summary of Allocated Related Party Employee Benefit Costs by Income Statement Line Item Schedule Of Entity Wide Information Allocated Related Party Employee Benefit Costs By Income Statement Line [Table Text Block] Schedule Of Entity Wide Information Allocated Related Party Employee Benefit Costs By Income Statement Line [Table Text Block] Schedule of Entity Wide Information Purchases from Related Parties Schedule Of Entity Wide Information Purchases From Related Parties [Table Text Block] Schedule Of Entity Wide Information Purchases From Related Parties [Table Text Block] Receivables from Related Parties Schedule of Current Receivables From Related Parties [Table Text Block] [Table Text Block] for Schedule of Current Receivables From Related Parties [Table] Schedule of Long Term Receivables with Related Parties Schedule of Long Term Receivables with Related Parties [Table Text Block] Schedule of Long Term Receivables with Related Parties [Table Text Block] Payables to Related Parties Schedule Of Payables To Related Parties [Table Text Block] Schedule Of Payables To Related Parties [Table Text Block] Schedule Of Related Party Deferred Revenue Table Schedule of Related Party Deferred Revenue [Table Text Block] Schedule of Related Party Deferred Revenue [Table Text Block] Minimum rental expense Operating Leases, Rent Expense LOOP and Explorer Loop Llc and Explorer Pipeline [Member] Loop Llc and Explorer Pipeline [Member] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] MPLX Holdings Inc MPLX Holdings Inc [Member] MPLX Holdings Inc [Member] MPLX Logistics LLC MPLX Logistics LLC [Member] MPLX Logistics LLC [Member] General Partner Common Units General Partner Common Units [Member] General Partner Common Units [Member] General Partner Units General Partner Units [Member] General Partner Units [Member] Payments to acquire interest in joint venture Payments to Acquire Interest in Joint Venture Equity interest issued or issuable, value assigned Business Acquisition, Equity Interest Issued or Issuable, Value Assigned Total consideration, value assigned Business Acquisition, Total Consideration, Value Assigned Value of equity interests (such as common shares, preferred shares, or partnership interest) issued or issuable and cash to acquire the entity. Equity interest issued or issuable, fair value assigned Business Acquisition, Equity Interest Issued or Issuable, Fair Value Assigned Fair value of equity interests (such as common shares, preferred shares, or partnership interest) issued or issuable to acquire the entity. Total consideration, fair value assigned Business Acquisition, Total Consideration, Fair Value Assigned Fair value of equity interests (such as common shares, preferred shares, or partnership interest) issued or issuable and cash paid to acquire the entity. Units, acquisitions Partners' Capital Account, Units, Acquisitions Aggregate percentage of general partner interest Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest Pipeline length Pipeline length Pipeline length Pipeline diameter Pipeline diameter Pipeline diameter Number of pump stations Number of Pump Stations Number of Pump Stations Defined benefit plan, AOCI, gain(loss) before tax Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax Contribution from MPC Capital Contribution By Related Party Capital Contribution By Related Party Select Quarterly Financial Data Quarterly Financial Information [Text Block] Schedule of Goodwill [Table] Schedule of Goodwill [Table] Goodwill [Line Items] Goodwill [Line Items] Gross goodwill Goodwill, Gross Accumulated impairment losses Goodwill, Impaired, Accumulated Impairment Loss Goodwill, beginning balance Goodwill Purchase price allocation adjustments Goodwill, Purchase Accounting Adjustments Impairment losses Acquisitions Goodwill, Acquired During Period Goodwill, ending balance Stockholders Equity [Table] Stockholders Equity [Table] Stockholders Equity [Table] General Partner And Limited Partner Units General Partner And Limited Partner [Member] Party to a partnership business who has both unlimited and limited liability. Stockholders Equity [Line Items] Stockholders Equity [Line Items] Stockholders Equity [Line Items] Number of units outstanding Partners' Capital Account, Units Common units outstanding Limited Partners' Capital Account, Units Outstanding Equity Method Investments Equity Method Investments [Table Text Block] Summarized Financial Information For Equity Method Investees Table Summarized Financial Information For Equity Method Investees Table [Table Text Block] Summarized financial information for equity method investees [Table Text Block] Risks and Uncertainties [Abstract] Major Customer and Concentration of Credit Risk [Table] Concentration Risk [Table] Customer [Axis] Customer [Axis] Customer [Domain] Customer [Domain] First Major Customer First Major Customer [Member] First Major Customer [Member] Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Revenues And Other Income] Revenues And Other Income [Member] Revenues And Other Income [Member] Concentration Risk [Line Items] Concentration Risk [Line Items] Concentration risk, percentage Concentration Risk, Percentage New Accounting Pronouncements and Changes in Accounting Principles [Abstract] Prospective Adoption of New Accounting Pronouncements [Table] Prospective Adoption of New Accounting Pronouncements [Table] Initial Application Period Cumulative Effect Transition [Axis] Initial Application Period Cumulative Effect Transition [Axis] Initial Application Period Cumulative Effect Transition [Domain] Initial Application Period Cumulative Effect Transition [Domain] Difference between Revenue Guidance in Effect before and after Topic 606 [Member] Difference between Revenue Guidance in Effect before and after Topic 606 [Member] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event Subsequent Event [Member] Third Party Reimbursements Third Party Reimbursements [Member] Third Party Reimbursements [Member] Non-cash Consideration Non-cash Consideration [Member] Non-cash Consideration [Member] Percent-of-Proceeds Percent-of-Proceeds [Member] Percent-of-Proceeds [Member] Imbalances Imbalances [Member] Imbalances [Member] Item Effected [Line Items] Item Effected [Line Items] Effects on cost of goods and services sold Cost of Goods and Services Sold Effects on revenue from contract with customer Revenue from Contract with Customer, Excluding Assessed Tax Property, Plant and Equipment [Abstract] Schedule of Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Assets Held under Capital Leases [Member] Assets Held under Capital Leases [Member] Gross assets Capital Leased Assets, Gross Accumulated depreciation Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Payables - related parties Due to Related Parties, Current Schedule of Stockholders Equity Schedule of Stockholders Equity [Table Text Block] Schedule Of Calculation Of Net Income Applicable to Partners Schedule Of Calculation Of Net Income Applicable to Partners [Table Text Block] [Table Text Block] for Schedule Of Calculation Of Net Income Applicable to Partners [Table] Distributions Made to Limited Partner, by Distribution Distributions Made to Limited Partner, by Distribution [Table Text Block] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Crude Oil Crude Oil [Member] Asset Class [Axis] Asset Class [Axis] Asset Class [Domain] Asset Class [Domain] Natural gas liquids storage caverns Natural gas liquids storage caverns [Member] Natural gas liquids storage caverns [Member] Light-product terminal Light-product terminal [Member] Light-product terminal [Member] Ownership Type [Axis] Ownership Type [Axis] Direct or Indirect Ownership Interest Ownership Type [Domain] Ownership Type [Domain] [Domain] for Direct or Indirect Ownership Interest Wholly Owned Properties Wholly Owned Properties [Member] Property Subject to Operating Lease Property Subject to Operating Lease [Member] Partially Owned Properties Partially Owned Properties [Member] Business Acquisition [Line Items] Business Acquisition [Line Items] Miles of pipeline Miles of pipeline Miles of pipeline Number of natural gas liquids storage caverns Number of natural gas liquids storage caverns Number of natural gas liquids storage caverns Storage capacity Storage Capacity Storage Capacity Number of light product terminals Number of light product terminals Number of light product terminals Related Party Agreements and Transactions Related Party Transactions Disclosure [Text Block] Fair Value Inputs, Assets and Liabilities, Quantitative Information [Table] Fair Value Inputs, Assets and Liabilities, Quantitative Information [Table] Schedule of the inputs used in the fair value measurement of assets and liabilities. This disclosure may include, but is not limited to, the fair value of the asset and liabilities, valuation technique used to measure fair value, the inputs used to measure fair value, the ranges of the inputs, and the weighted averages of the inputs. [Table] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Significant unobservable inputs (Level 3) Fair Value, Inputs, Level 3 [Member] Embedded derivatives in commodity contracts Embedded Derivative Financial Instruments [Member] Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] [Line Items] for Schedule of the inputs used in the fair value measurement of assets and liabilities. This disclosure may include, but is not limited to, the fair value of the asset and liabilities, valuation technique used to measure fair value, the inputs used to measure fair value, the ranges of the inputs, and the weighted averages of the inputs. [Table] Fair value inputs commodity price Fair Value Inputs Forward Commodity Price Represents the forward commodity price used as an input to measure fair value. Probability of renewal, first term Fair Value Inputs Probability of Renewal Represents the percentage of likelihood of renewal of the commodity contract with embedded derivative. Term of counterparty option to renew gas purchase agreement Embedded Derivative Renewal Term Represents the term for which the counterparty has the option to renew a purchase agreement related to an embedded derivative. Probability of renewal, second term Fair Value Inputs Probability of Renewal Second Term Represents the percentage of likelihood of renewal of the commodity contract with embedded derivative for the second term of the contract. Accounting Standards New Accounting Pronouncements and Changes in Accounting Principles [Text Block] Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Fair Value Inputs Assets and Liabilities Quantitative Information [Table Text Block] Fair Value Inputs Assets and Liabilities Quantitative Information [Table Text Block] Tabular disclosure of quantitative information about the inputs used in the fair value measurement of assets and liabilities classified as Level 3 measurements. This disclosure may include, but is not limited to, the fair value of the asset and liabilities, valuation technique used to measure fair value, the inputs used to measure fair value, the ranges of the inputs, and the weighted averages of the inputs. Schedule of changes in Level 3 fair value measurements [Table Text Block] Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Fair Value, by Balance Sheet Grouping [Table Text Block] Fair Value, by Balance Sheet Grouping [Table Text Block] Natural gas gathering and NGL transportation pipelines and facilities Gas Gathering And Transmission Equipment And Facilities [Member] Long-lived, depreciable assets related to natural gas gathering and NGL transportation pipelines and facilities. Processing, fractionation and storage facilities(1) Processing, Fractionation And Storage Facilities [Member] Represents the long-lived depreciable assets for processing, fractionation and storage facilities. Pipelines and related assets Pipelines And Related Assets [Member] Pipelines and related assets. Barges and towing vessels Barges and towing vessels [Member] Barges and towing vessels [Member] Terminals and related assets(1) Terminals and related assets [Member] Terminals and related assets Land, building, office equipment and other Land Building Office Equipment And Other [Member] Represents real estate held for productive use, long-lived structures used in the conduct of business, including office, production, storage, building improvements and distribution facilities and includes long-lived, depreciable assets not directly used in the production process for inventories or facilities. Estimated useful lives Property, Plant and Equipment, Useful Life Property, plant and equipment, gross Property, Plant and Equipment, Gross Less accumulated depreciation Property, plant and equipment, net Property, Plant and Equipment, Net Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Intrinsic value of units issued during the period Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period Total Intrinsic Value 1 Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period Total Intrinsic Value1 Document And Entity Information [Abstract] Document and Entity Information [Abstract] Document Information [Table] Document Information [Table] Common Units Common Stock Units [Member] Common Stock Units [Member] Class B Units Class B Units [Member] Class B Units [Member] Entity Information [Line Items] Entity Information [Line Items] Document Type Document Type Amendment Flag Amendment Flag Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Trading Symbol Trading Symbol Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Entity Current Reporting Status Entity Current Reporting Status Entity Voluntary Filers Entity Voluntary Filers Entity Filer Category Entity Filer Category Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Entity Public Float Entity Public Float Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Fair Value, Measurements, Recurring [Member] Fair Value, Measurements, Recurring [Member] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Assets Derivative Asset Liabilities Derivative Liability Summary of Unit Award Activity Schedule of Share-based Compensation, Restricted Stock Units Award Activity [Table Text Block] Schedule of Share-based Compensation Arrangement by Share-based Payment Award, Restricted Stock Units, Vested and Expected to Vest Share-based Compensation Arrangements by Share-based Payment Award, Restricted Stock Units, Vested and Expected to Vest [Table Text Block] Schedule of Share-based Compensation, Performance Unit Awards, Valuation Assumptions Schedule of Share-based Compensation, Performance Unit Awards, Valuation Assumptions [Table Text Block] Schedule of Share-based Compensation, Performance Unit Awards, Valuation Assumptions [Table Text Block] Net Income (Loss) Per Limited Partner Unit Earnings Per Share [Text Block] Limited Partner Limited Partner [Member] Equity interest issued or issuable, number of shares Business Acquisition, Equity Interest Issued or Issuable, Number of Shares Number of tow boats Number of Tow Boats Number of Tow Boats Number of barges Number of barges Number of barges Percent of volumes shipped Percent of Volumes Shipped Percent of Volumes Shipped Revenues and other income Business Acquisition, Pro Forma Revenue Net income attributable to MPLX LP Business Acquisition, Pro Forma Net Income (Loss) Net income attributable to MPLX LP per unit - basic Business Acquisition, Pro Forma Earnings Per Share, Basic Net income attributable to MPLX LP per unit - diluted Business Acquisition, Pro Forma Earnings Per Share, Diluted Pro forma information, description Business Acquisition, Pro Forma Information, Description Statement of Financial Position [Abstract] Limited Partners Class B Units Limited Partners Class B Units [Member] Limited Partners Class B Units [Member] Common Unitholder GP Units issued Limited Partners' Capital Account, Units Issued Units outstanding Units issued General Partners' Capital Account, Units Issued Units outstanding General Partners' Capital Account, Units Outstanding Property Subject to or Available for Operating Lease, by Major Property Class [Table] Property Subject to or Available for Operating Lease, by Major Property Class [Table] Major Property Class [Axis] Major Property Class [Axis] Major Property Class [Domain] Major Property Class [Domain] Construction-in-progress Construction in Progress [Member] Property Subject to or Available for Operating Lease [Line Items] Property Subject to or Available for Operating Lease [Line Items] Total Property Subject to or Available for Operating Lease, Gross Less accumulated depreciation Property Subject to or Available for Operating Lease, Accumulated Depreciation Property, plant and equipment, net Property Subject to or Available for Operating Lease, Net Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block] Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block] Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block] Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block] Derivative Instruments, Gain (Loss) [Table Text Block] Derivative Instruments, Gain (Loss) [Table Text Block] Steam Methane Reformer Held Under Financing Arrangement [Member] Steam Methane Reformer Held Under Financing Arrangement [Member] A steam methane reformer (SMR) sold in a transaction treated as a financing arrangement. Proceeds from liability Proceeds from Liability The cash inflow from a financing transaction. Imputed interest rate on liability Imputed Interest Rate on Liability Represents the imputed interest rate on a transaction treated as a financing arrangement. Property, plant and equipment, net Accrued liabilities Accrued Liabilities, Current Deferred credits and other liabilities Deferred Credits and Other Liabilities, Noncurrent Suppplemental Cash Flow [Table] [Table] Suppplemental Cash Flow [Table] [Table] Suppplemental Cash Flow [Table] [Table] Related Party 364-day Term Loan Related Party 364-day Term Loan [Member] Related Party 364-day Term Loan [Member] Suppplemental Cash Flow [Line Items] Suppplemental Cash Flow [Line Items] [Line Items] for Suppplemental Cash Flow Debt issuance costs, gross Debt Issuance Costs, Gross Accounts payable, related parties Accounts Payable, Related Parties Ozark Pipeline Ozark Pipeline [Member] Ozark Pipeline [Member] Components Of The Fair Value Of Consideration Transferred Components Of The Fair Value Of Consideration Transferred [Table Text Block] Components of the Fair Value of Consideration Transferred Table [Text Block] Historical Information for Deconsolidated Entity Historical Information for Deconsolidated Entity [Table Text Block] Historical Information for Deconsolidated Entity [Table Text Block] Schedule of Recognized Identified Assets Acquired and Liabilities Assumed Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block] Business Acquisition, Pro Forma Information Business Acquisition, Pro Forma Information [Table Text Block] Lease Operations Lessor, Operating Leases [Text Block] Reconciliation to Net Income Attributable to Noncontrolling Interests [Table] Reconciliation to Net Income Attributable to Noncontrolling Interests [Table] Reconciliation to Net Income Attributable to Noncontrolling Interests [Table] Reconciliation to Net Income Attributable to Noncontrolling Interests [Line Items] Reconciliation to Net Income Attributable to Noncontrolling Interests [Line Items] [Line Items] for Reconciliation to Net Income Attributable to Noncontrolling Interests [Table] Portion of noncontrolling interests and Predecessor related to items below segment income from operations Portion of NCI and Predecessor related to items below segment operating income Portion of NCI and Predecessor related to items below segment operating income Portion of operating income attributable to noncontrolling interests of unconsolidated affiliates Portion of operating income attributable to NCI of unconsolidated affiliates Portion of operating income attributable to NCI of unconsolidated affiliates Net income attributable to noncontrolling interests and Predecessor Net Income Loss Attributable to Noncontrolling Interest and Predecessor Amount of Net Income (Loss) attributable to noncontrolling interest and Predecessor. Receivables - related parties Accounts Receivable, Related Parties, Current Supplemental Cash Flow Information Cash Flow, Supplemental Disclosures [Text Block] 2018 Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months 2019 Long-term Debt, Maturities, Repayments of Principal in Year Two 2020 Long-term Debt, Maturities, Repayments of Principal in Year Three 2021 Long-term Debt, Maturities, Repayments of Principal in Year Four 2022 Long-term Debt, Maturities, Repayments of Principal after Year Five Payments to acquire property, plant, and equipment Pipeline barrels handled Pipeline Barrels Handled Pipeline Barrels Handled Revenues and other income Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual Income from operations Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual Contractual Obligation, Fiscal Year Maturity Schedule Contractual Obligation, Fiscal Year Maturity Schedule [Table Text Block] Schedule Of Future Minimum Lease Payments For Operating And Capital Leases Table Schedule Of Future Minimum Lease Payments For Operating And Capital Leases Table [Text Block] Schedule of future minimum lease payments for operating and capital leases [Table Text Block]. Schedule of Rent Expense Schedule of Rent Expense [Table Text Block] Schedule of Minimum Amounts Payable Annually Under the Product Supply Agreement Recorded Unconditional Purchase Obligations [Table Text Block] Summary of Outstanding Borrowings Schedule of Debt [Table Text Block] Schedule of Debt Payments Schedule of Maturities of Long-term Debt [Table Text Block] Schedule of interest payable dates Schedule of interest payable dates [Table Text Block] Schedule of interest payable dates [Table Text Block] Schedule of amounts related to the SMR included in the Balance Sheet Schedule of Disposals Treated as Financing Arrangement Disclosures [Text Block] Tabular disclosure of disposal that was accounted for as a financing arrangement due to the Company's continuing involvement in the underlying in-substance real estate. The disclosure includes the classification and carrying value of the assets and liabilities that remain on the consolidated balance sheet as a result of the financing treatment. Equity Method Investments Equity Method Investments [Member] Goodwill Goodwill [Member] Valuation Technique [Axis] Valuation Technique [Axis] Valuation Technique [Domain] Valuation Technique [Domain] Income Approach Valuation Technique Income Approach Valuation Technique [Member] Number of reporting units Number of Reporting Units Number of reporting units impaired Number of Reporting Units Impaired Number of Reporting Units Impaired Discount rate Fair Value Inputs, Discount Rate Attrition rate Fair Value Inputs, Attrition Rate Fair Value Inputs, Attrition Rate Summary of Principal Accounting Policies Significant Accounting Policies [Text Block] Statement of Stockholders' Equity [Abstract] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] AOCI Attributable to Parent AOCI Attributable to Parent [Member] Noncontrolling Interest Noncontrolling Interest [Member] Equity of Predecessor Retained Earnings [Member] Beginning balance Partners' Capital, Including Portion Attributable to Noncontrolling Interest Distributions to MPC from Predecessor Distributions to MPC from Predecessor Distributions to MPC from Predecessor Contribution of MarkWest Hydrocarbon from MPC Partners' Capital Account, Contributions Distribution of MarkWest Hydrocarbon to MPC Noncash Partner Capital Account Distributions Noncash distributions to partners. Issuance of units under ATM Program Partners' Capital Account, Sale of Units Net income (loss) Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Temporary Equity The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest and excluding the portion attributable to temporary equity. Allocation of MPC's net investment at acquisition Stockholders' Equity, Change in Reporting Entity Distribution to MPC for acquisitions Partners' Capital Account, Acquisitions Contributions from MPC - MarkWest Merger Capital Contribution By Related Party - MarkWest Merger Capital Contribution By Related Party - MarkWest Merger Distributions to unitholders and general partner Partners' Capital Account, Distributions Distributions to noncontrolling interests Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Contributions from noncontrolling interests Proceeds from Noncontrolling Interests Unit conversion Partners' Capital Account, Exchanges and Conversions Non-cash contribution from MPC Non-Cash Contribution from MPC Non-Cash Contribution from MPC Equity-based compensation Partners' Capital Account, Unit-based Compensation Deferred income tax impact from changes in equity Deferred income tax impact from changes in equity Deferred income tax impact from changes in equity Issuance of units in MarkWest Merger Stock Issued During Period, Value, Acquisitions Noncontrolling interests assumed in MarkWest Merger Noncontrolling Interest, Increase from Business Combination Ending balance Business Acquisition [Table] Business Acquisition [Table] Business Acquisition [Table] Pipe Line Holding Pipe Line Holding [Member] Pipe Line Holding [Member] Percentage of partners interest acquired Percentage Of Partners Interest Acquired Percentage Of Partners Interest Acquired Purchase of additional interest in Pipe Line Holdings Parent ownership interest, changes, purchase of interest by parent Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Changes, Purchase of Interest by Parent Ownership interest Subsidiary of Limited Liability Company or Limited Partnership, Ownership Interest Schedule of Net Income Per Limited Partner Unit Schedule of Distributions By Partner By Class [Table Text Block] Schedule of Distributions By Partner By Class [Table Text Block] Schedule of Basic and Diluted Earnings Per Unit Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Summary of Inventories Schedule of Inventory, Current [Table Text Block] Subsequent Events [Abstract] Subsequent Events Subsequent Events [Text Block] Major Customers and Concentration of Credit Risk Concentration Risk Disclosure [Text Block] Scenario [Axis] Scenario [Axis] Scenario, Unspecified [Domain] Scenario, Unspecified [Domain] Scenario, Previously Reported Scenario, Previously Reported [Member] Scenario, Adjustment Scenario, Adjustment [Member] Adjustments for Error Corrections [Axis] Adjustments for Error Corrections [Axis] Adjustments for Error Correction [Domain] Adjustments for Error Correction [Domain] Misstatement of Original Purchase Price Allocation [Member] Misstatement of Original Purchase Price Allocation [Member] Misstatement of Original Purchase Price Allocation [Member] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Customer Relationships Customer Relationships [Member] Finite-Lived Intangible Assets Finite-Lived Intangible Assets [Member] Selling, General and Administrative Expenses Selling, General and Administrative Expenses [Member] Nonoperating Income (Expense) Nonoperating Income (Expense) [Member] Common units conversion ratio Common Units Conversion Ratio Ratio applied to the conversion of Markwest shares to MPLX common units. Cash consideration to unitholders Cash consideration to unitholders Cash payment per unit to unitholders for acquisition Class B units conversion ratio Class B Units Conversion Ratio Class B Units Conversion Ratio Payable to seller Business Combination, Consideration Transferred, Liabilities Incurred Fair value of units issued Business Combination, Consideration Transferred, Equity Interests Issued and Issuable Total fair value of consideration transferred Business Combination, Consideration Transferred, Including Equity Interest in Acquiree Held Prior to Combination Cash and cash equivalents Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents Receivables Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables Inventories Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory Other current assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other Equity method investments Business Combination, Recognized Identifiable Assets Acquired, Equity Method Investments Business Combination, Recognized Identifiable Assets Acquired, Equity Method Investments Property, plant and equipment Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment Intangibles Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles Other noncurrent assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets Total assets acquired Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets Accounts payable Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable Accrued liabilities Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Current Liabilities Payroll And Benefits Payable Amount of liabilities incurred for payroll and benefits assumed at the acquisition date. Accrued taxes Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Accrued Taxes Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Accrued Taxes Other current liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other Long-term debt Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt Deferred income taxes