Related Party Transactions [Abstract] Schedule of Related Party Transactions, by Related Party [Table] Schedule of Related Party Transactions, by Related Party [Table] 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] Related Party [Axis] Related Party [Axis] Related Party [Domain] Related Party [Domain] MPC Marathon Petroleum Corporation [Member] Marathon petroleum corporation. MarkWest Utica EMG MarkWest Utica EMG [Member] MarkWest Utica EMG [Member] Ohio Gathering Ohio Gathering Company, LLC [Member] Ohio Gathering Company, LLC [Member] Sherwood Midstream Sherwood Midstream [Member] Sherwood Midstream [Member] Other Other Affiliates [Member] MPC Investment MPC Investment [Member] MPC Investment [Member] Related Party Transaction [Line Items] Related Party Transaction [Line Items] Payables - related parties Due to Related Parties, Current Supplemental Cash Flow Elements [Abstract] Supplemental Cash Flow Information [Text Block] Cash Flow, Supplemental Disclosures [Text Block] Segment Reporting [Abstract] Schedule of Segment Reporting Information, by Segment [Table Text Block] Schedule of Segment Reporting Information, by Segment [Table Text Block] Reconciliation of Assets from Segment to Consolidated [Table Text Block] Reconciliation of Assets from Segment to Consolidated [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] Earnings Per Share [Abstract] Schedule of Distributions By Partner By Class 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] Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Equity-Based Compensation Plan Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Revenue from Contract with Customer [Abstract] Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Product and Service [Axis] Product and Service [Axis] Product and Service [Domain] Product and Service [Domain] Product [Member] Product [Member] Service [Member] Service [Member] Service, Other [Member] Service, Other [Member] Non-ASC 606 Revenue [Axis] Non-ASC 606 Revenue [Axis] Non-ASC 606 Revenue [Axis] Non-ASC 606 Revenue [Domain] Non-ASC 606 Revenue [Domain] [Domain] for Non-ASC 606 Revenue [Axis] Other Income [Member] Other Income [Member] Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Product sales Product Sales [Member] Product Sales [Member] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] 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] Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Total revenues from contracts with customers Revenue from Contract with Customer, Excluding Assessed Tax Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties Revenue from Contract with Customer, excluding Assessed Tax and Non-ASC 606 Revenue Revenue from Contract with Customer, excluding Assessed Tax and Non-ASC 606 Revenue Revenue from Contract with Customer, excluding Assessed Tax and Non-ASC 606 Revenue Other income Other Operating Income Total segment revenues and other income Revenues Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Restricted cash Restricted Cash Cash, cash equivalents and restricted cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Statement [Table] Statement [Table] 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] 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] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] ASC 606 Accounting Standards Update 2014-09 [Member] 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] Cumulative Adjusted 606 Balance Cumulative Adjusted 606 Balance [Member] Cumulative Adjusted 606 Balance [Member] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Inventories Inventories [Member] Property, plant and equipment Property, Plant and Equipment [Member] Long-term deferred revenue Deferred Revenue, Noncurrent [Member] Deferred Revenue, Noncurrent [Member] Equity Equity [Member] Statement [Line Items] Statement [Line Items] Cumulative effect of new accounting principle in period of adoption Cumulative Effect of New Accounting Principle in Period of Adoption Inventories Inventory, Gross Property, plant and equipment, net Property, Plant and Equipment, Net Long-term deferred revenue Deferred Revenue, Noncurrent Common unitholders - public Partners' Capital Fair Value Disclosures [Abstract] Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] Commodity Derivative Contracts (net) Commodity Contract [Member] Embedded Derivatives in Commodity Contracts (net) Embedded Derivative Financial Instruments [Member] Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair value at beginning of period Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs Total gains (losses) (realized and unrealized) included in earnings Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings Settlements Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Settlements Fair value at end of period The amount of total gains (losses) for the period included in earnings attributable to the change in unrealized losses relating to liabilities still held at end of period Fair Value Measurement with Unobservable Inputs Reconciliation, Recurring Basis Asset and Liabilities Net, Change in Unrealized Gain (Loss) Included in Earnings Contract Held This element represents total unrealized gains or losses for the period, arising from assets and liabilities measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in earnings. Such unrealized gains or losses relate to those contracts still held at the reporting date. Difference between Revenue Guidance in Effect before and after Topic 606 Difference between Revenue Guidance in Effect before and after Topic 606 [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] Oil Allowances Oil Allowances [Member] Oil Allowances [Member] Rental income Operating Leases, Income Statement, Lease Revenue Cost of revenues Cost of Goods and Services Sold Service revenue - product related Sales Revenue Services, Product Related Sales Revenue Services, Product Related Rental cost of sales Cost of Rental Sales and Occupancy Costs Cost of Rental Sales and Occupancy Costs Equity Transactions And Share Based Compensation [Table] Equity Transactions And Share Based Compensation [Table] Equity Transactions And Share Based Compensation [Table] Award Type [Axis] Award Type [Axis] Equity Award [Domain] Equity Award [Domain] Phantom Units Phantom Share Units (PSUs) [Member] Performance Shares [Member] Performance Shares [Member] Equity Transactions And Share Based Compensation [Line Items] Equity Transactions And Share Based Compensation [Line Items] Equity Transactions And Share Based Compensation [Line Items] Summary of Share-based Compensation, Restricted Stock Units Award Activity Schedule of Share-based Compensation, Restricted Stock Units Award Activity [Table Text Block] Equity [Abstract] Equity Stockholders' Equity Note Disclosure [Text Block] Property, Plant and Equipment [Abstract] Summary of Property, Plant and Equipment Property, Plant and Equipment [Table Text Block] Schedule of Sales to 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 from 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 [Table Text Block] 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] Schedule of Employee Services Expenses from Related Parties 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] Schedule of 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] Schedule of Payables to Related Parties Schedule Of Payables To Related Parties [Table Text Block] Schedule Of Payables To Related Parties [Table Text Block] Summary of Deferred Revenue - Related Parties Schedule of Related Party Deferred Revenue [Table Text Block] Schedule of Related Party Deferred Revenue [Table Text Block] Accounting Policies [Abstract] Use of Estimates Use of Estimates, Policy [Policy Text Block] Earnings Per Share Earnings Per Share, Policy [Policy Text Block] Revenue Recognition Revenue Recognition, Policy [Policy Text Block] Temporary Equity Disclosure [Abstract] Redeemable Preferred Units Temporary Equity Disclosure [Text Block] Temporary Equity Disclosure [Text Block] Commitments and Contingencies Disclosure [Abstract] Commitments And Contingencies [Table] Commitments And Contingencies [Table] Commitments And Contingencies [Table] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] Markwest Liberty Midstream [Member] Markwest Liberty Midstream [Member] Markwest Liberty Midstream [Member] Litigation Case [Axis] Litigation Case [Axis] Litigation Case [Domain] Litigation Case [Domain] MarkWest, MarkWest Liberty Midstream, MarkWest Bluestone, Ohio Fractionation, MarkWest Utica EMG [Member] [Member] MarkWest, MarkWest Liberty Midstream, MarkWest Bluestone, Ohio Fractionation, MarkWest Utica EMG [Member] [Member] MarkWest, MarkWest Liberty Midstream, MarkWest Bluestone, Ohio Fractionation, MarkWest Utica EMG, collectively the "MPLX Parties" Bilfinger Westcon, Inc. [Member] Bilfinger Westcon, Inc. [Member] Bilfinger Westcon, Inc. Litigation [Member] Apex [Member] Apex [Member] Apex [Member] Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Environmental Loss Contingency [Member] Environmental Loss Contingency [Member] Environmental Loss Contingency [Member] Commitments And Contingencies [Line Items] Commitments And Contingencies [Line Items] Commitments And Contingencies [Line Items] Accrued liabilities for environmental remediation Accrual for Environmental Loss Contingencies Receivables from MPC for indemnification of environmental costs Due from Related Parties, Current EPA proposed penalty EPA Proposed Penalty EPA Proposed Penalty Estimated cost of proposed supplemental environmental projects Estimated cost of proposed supplemental environmental projects Estimated cost of proposed supplemental environmental projects Loss Contingency, Damages Sought, Value Loss Contingency, Damages Sought, Value Apex litigation settlement amount Litigation Settlement, Amount Awarded to Other Party Contractual commitments to acquire property, plant and equipment Purchase Commitment, Remaining Minimum Amount Committed Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Comprehensive Income (Loss) Note [Text Block] Related Party Agreements and Transactions Related Party Transactions Disclosure [Text Block] Derivative Instruments and Hedging Activities Disclosure [Abstract] Derivative [Table] Derivative [Table] Hedging Designation [Axis] Hedging Designation [Axis] Hedging Designation [Domain] Hedging Designation [Domain] Not Designated as Hedging Instrument [Member] Not Designated as Hedging Instrument [Member] Other Noncurrent Liabilities [Member] Other Noncurrent Liabilities [Member] Commodity Type [Axis] Commodity Type [Axis] Disclosure pertaining to different commodity types. Commodity Type [Domain] Commodity Type [Domain] Represents the information pertaining to all types of commodity. Natural Gas [Member] Natural Gas [Member] Derivative instrument whose primary underlying risk is tied to the price of natural gas. Commodity contracts Embedded derivatives in commodity contracts Derivative [Line Items] Derivative [Line Items] Number of Renewals Number of Renewals Number of Times for Automatic Renewal Embedded Derivative Renewal Term Embedded Derivative Renewal Term Represents the term for which the counterparty has the option to renew a purchase agreement related to an embedded derivative. Embedded Derivative Fair Value of Embedded Derivative Liability Including Inception Value Allocable to Host Contract Embedded Derivative Fair Value of Embedded Derivative Liability Including Inception Value Allocable to Host Contract Fair value as of the balance sheet date of a natural gas purchase agreement embedded in a gas processing agreement. The natural gas purchase agreement is an embedded derivative. This amount includes the value of the embedded purchase agreement at the inception of the arrangement. however, in accordance with GAAP, the fair value of the embedded derivative at inception is deemed to be allocable to the host contract and is not separately recorded as an embedded derivative. Long-term receivables - related parties Due from Related Parties, Noncurrent Statement of Stockholders' Equity [Abstract] Accumulated Other Comprehensive Loss AOCI Attributable to Parent [Member] Noncontrolling Interests Noncontrolling Interest [Member] Equity of Predecessor Retained Earnings [Member] Class B Unitholders Limited Partners Class B Units [Member] Limited Partners Class B Units [Member] General Partner General Partner [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 Issuance of units under ATM Program Partners' Capital Account, Sale of Units Net income (excludes amounts attributable to preferred units) 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. Contribution from MPC Capital Contribution By Related Party Capital Contribution By Related Party Allocation of MPC's net investment at acquisition Stockholders' Equity, Change in Reporting Entity Distribution to MPC for acquisitions Partners' Capital Account, Acquisitions Distributions to unitholders 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 Partners' Capital Account, Exchanges and Conversions Partners' Capital Account, Exchanges and Conversions Equity-based compensation Partners' Capital Account, Unit-based Compensation Other Stockholders' Equity, Other Ending Balance 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 LP 2012 Incentive Compensation Plan [Member] Mplx Two Thousand Twelve Incentive Compensation Plan [Member] Mplx two thousand twelve incentive compensation plan. Common Stock, Capital Shares Reserved for Future Issuance Common Stock, Capital Shares Reserved for Future Issuance 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 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 Performance units grant date fair value (in USD per unit) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Deferred Revenue Arrangement Type [Axis] Deferred Revenue Arrangement Type [Axis] Deferred Revenue [Domain] Deferred Revenue [Domain] Minimum volume deficiencies [Member] Minimum Committed Volume Contracts [Member] Minimum Committed Volume Contracts [Member] Project reimbursements [Member] Reimbursable Projects [Member] Reimbursable Projects [Member] Deferred revenue related parties Deferred Revenue Related Parties Deferred revenue with related parties, including both current and non current portions. Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Operating Segments Operating Segments [Member] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Income from equity method investments Income (Loss) from Equity Method Investments Other income Adjusted EBITDA Adjusted EBITDA Adjusted EBITDA Capital Expenditure Maintenance Capital Expenditures Maintenance Capital Expenditures Growth Capital Expenditures Growth Capital Expenditures Growth Capital Expenditures Equity Method Investments and Joint Ventures [Abstract] Schedule of Equity Method Investments [Table] Schedule of Equity Method Investments [Table] Sherwood Midstream Sherwood Midstream LLC [Member] Sherwood Midstream LLC Ownership Type [Axis] Ownership Type [Axis] Direct or Indirect Ownership Interest Ownership Type [Domain] Ownership Type [Domain] [Domain] for Direct or Indirect Ownership Interest Direct Ownership Interest [Member] Direct Ownership Interest [Member] Direct ownership interest [Member] Indirect Ownership Interest [Member] Indirect Ownership Interest [Member] Indirect Ownership Interest Investment, Name [Axis] Investment, Name [Axis] Investment, Name [Domain] Investment, Name [Domain] Sherwood Midstream Holdings Sherwood Midstream Holdings [Member] Sherwood Midstream Holdings [Member] Schedule of Equity Method Investments [Line Items] Schedule of Equity Method Investments [Line Items] Fair Value Of Assets Contributed Fair Value Of Assets Contributed The fair value of assets contributed to the Partnership in noncash investing or financing activities. Equity method investment, ownership percentage Equity Method Investment, Ownership Percentage Payments to acquire interest in joint venture Payments to Acquire Interest in Joint Venture Ownership Interest In Assets Sold By Company In Affiliate Ownership Interest In Assets Sold By Company In Affiliate Ownership Interest In Assets Sold By Company In Affiliate Proceeds From Sale Of Ownership Interest In Assets Sold By Company In Affiliate Proceeds From Sale Of Ownership Interest In Assets Sold By Company In Affiliate Proceeds From Sale Of Ownership Interest In Assets Sold By Company In Affiliate Revenue, Initial Application Period Cumulative Effect Transition [Table] Revenue, Initial Application Period Cumulative Effect Transition [Table] Oil and Gas, Refining and Marketing [Member] Oil and Gas, Refining and Marketing [Member] Natural Gas, Midstream [Member] Natural Gas, Midstream [Member] Calculated under Revenue Guidance in Effect before Topic 606 [Member] Calculated under Revenue Guidance in Effect before Topic 606 [Member] Revenue, Initial Application Period Cumulative Effect Transition [Line Items] Revenue, Initial Application Period Cumulative Effect Transition [Line Items] Revenues and other income: Revenues And Other Income [Abstract] Revenues and Other Income [Abstract] Costs and expenses: Costs and Expenses [Abstract] Cost of Goods and Services Sold Depreciation and amortization Depreciation Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net Business Combinations [Abstract] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Mt. Airy Terminal [Member] Mt. Airy Terminal [Member] Mt. Airy Terminal [Member] Payments to Acquire Businesses, Gross Payments to Acquire Businesses, Gross Storage Capacity Storage Capacity Storage Capacity Barrels Handled Barrels Handled Barrels Handled Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment Goodwill Goodwill Statement of Comprehensive Income [Abstract] Other comprehensive income/(loss), net of tax: Other Comprehensive Income (Loss), Net of Tax [Abstract] Remeasurements of pension and other postretirement benefits related to equity method investments, net of tax Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Adjustment, Net of Tax Amount after tax and reclassification adjustments, of increase (decrease) in accumulated other comprehensive income (loss) related to the net actuarial gain (loss) of pension and other postretirement defined benefit plans. Comprehensive income Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Less comprehensive income attributable to: Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest [Abstract] Noncontrolling interests Comprehensive Income (Loss), Net of Tax, Attributable to Nonredeemable Noncontrolling Interest Comprehensive Income (Loss), Net of Tax, Attributable to Nonredeemable Noncontrolling Interest Income attributable to Predecessor Comprehensive Income (loss), Net of Tax, Attributable to Predecessor Comprehensive Income (loss), Net of Tax, Attributable to Predecessor Comprehensive income attributable to MPLX LP Comprehensive Income (Loss), Net of Tax, Attributable to Parent Disposal Group Classification [Axis] Disposal Group Classification [Axis] Disposal Group Classification [Domain] Disposal Group Classification [Domain] Equity Method Investments [Table Text Block] Equity Method Investments [Table Text Block] Summarized Financial Information For Equity Method Investees Table [Table Text Block] Summarized Financial Information For Equity Method Investees Table [Table Text Block] Summarized financial information for equity method investees [Table Text Block] Centrahoma Processing LLC [Member] Centrahoma Processing LLC [Member] Centrahoma Processing LLC [Member] Explorer Explorer Pipeline [Member] Explorer Pipeline [Member] Illinois Extension Illinois Extension Pipeline Company LLC [Member] Illinois Extension Pipeline Company LLC [Member] LOCAP Locap Llc [Member] Locap Llc [Member] LOOP Loop Llc [Member] LOOP LLC [Member] MarEn Bakken Company LLC [Member] MarEn Bakken Company LLC [Member] MarEn Bakken 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] Other VIEs and Non-VIEs [Member] Other VIEs and Non-VIEs [Member] Other VIEs and Non-VIEs [Member] Other VIEs [Member] Other VIEs [Member] Other VIEs [Member] Non-VIEs [Member] Non-VIEs [Member] Non-VIEs [Member] Equity method investments Equity Method Investments Revenues 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 Difference between carrying amount and underlying equity Equity Method Investment, Difference Between Carrying Amount and Underlying Equity Difference between carrying amount and underlying equity portion related to goodwill 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 Stockholders Equity Note [Table] Stockholders Equity Note [Table] Stockholders Equity Note [Table] Stockholders Equity Note [Line Items] Stockholders Equity Note [Line Items] Stockholders Equity Note [Line Items] Conversion of GP economic interests Partners' Capital Account, Units, Converted Partners' Capital Account, Exchanges and Conversions Segment Reporting Disclosure [Text Block] Segment Reporting Disclosure [Text Block] Related party purchases Related Party Transaction, Purchases from Related Party Acquisitions Business Combination Disclosure [Text Block] Rollforward of Redeemable Preferred Units Temporary Equity [Table Text Block] Derivative Instruments and Hedging Activities Disclosure [Text Block] Derivative Instruments and Hedging Activities Disclosure [Text Block] Acquisitions Equity Method Investments and Joint Ventures [Abstract] Acquisitions Equity Method Investments and Joint Ventures [Abstract] MarEn Bakken [Member] MarEn Bakken [Member] MarEn Bakken [Member] Bakken Pipeline System [Member] Bakken Pipeline System [Member] Bakken Pipeline System [Member] Investments in unconsolidated affiliates Payments to Acquire Equity Method Investments Percentage of Ownership Interest in Joint Venture Acquired Percentage of Ownership Interest in Joint Venture Acquired Percentage of Ownership Interest in Joint Venture Acquired Incentive Distribution Rights Forfeited per Quarter Incentive Distribution Rights Forfeited per Quarter Incentive Distribution Rights Forfeited per Quarter Number of Quarters IDRs Forfeited Number of Quarters IDRs Forfeited Number of Quarters IDRs Forfeited Prorated Incentive Distribution Rights Forfeited Prorated Incentive Distribution Rights Forfeited Prorated Incentive Distribution Rights Forfeited Revenue from Contract with Customer [Text Block] Revenue from Contract with Customer [Text Block] 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] Retirement Plan Type [Axis] Retirement Plan Type [Axis] Retirement Plan Type [Domain] Retirement Plan Type [Domain] Pension Plan [Member] Pension Plan [Member] Other Postretirement Benefits Plan [Member] Other Postretirement Benefits Plan [Member] Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Other Comprehensive Income (Loss), Net of Tax Other Comprehensive Income (Loss), Net of Tax Net Income Per Limited Partner Unit Earnings Per Share [Text Block] Rental cost of sales - related parties Rental cost of sales - related parties [Member] Rental cost of sales - related parties [Member] Purchases - related parties Purchases From Related Parties [Member] Purchases From Related Parties [Member] General and administrative expenses General and Administrative Expense - Related Party [Member] General and Administrative Expense - Related Party [Member] Charges for services under an omnibus agreement Related Party Transaction, Expenses from Transactions with Related Party Stockholders Equity [Table] Stockholders Equity [Table] Stockholders Equity [Table] Refining Logistics & Fuels Distribution Refining Logistics & Fuels Distribution [Member] Refining Logistics & Fuels Distribution [Member] General Partner Units General Partner Units [Member] General Partner Units [Member] Stockholders Equity [Line Items] Stockholders Equity [Line Items] Stockholders Equity [Line Items] Balance at December 31, 2017 Partners' Capital Account, Units Unit-based compensation awards Partners' Capital Account, Units, Unit-based Compensation Contribution of refining logistics and fuels distribution assets Partners' Capital Account, Units, Acquisitions Balance at September 30, 2018 Sale of units for GP Interest General partner ownership interest Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] 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 Schedule of Incentive Distribution Made to Managing Member or General Partner [Table] Schedule of Incentive Distribution Made to Managing Member or General Partner [Table] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event Subsequent Event [Member] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] Preferred Units Preferred Stock [Member] Incentive Distribution Made to Managing Member or General Partner [Line Items] Incentive Distribution Made to Managing Member or General Partner [Line Items] Declaration date Distribution Made to Limited Partner, Declaration Date Distributions declared (including IDRs) Distribution Made to Limited Partner, Cash Distributions Declared Cash distributions declared per limited partner common unit Distribution Made to Limited Partner, Distributions Declared, Per Unit Distribution date Distribution Made to Limited Partner, Distribution Date Date of record Distribution Made to Limited Partner, Date of Record General partner's distributions Managing Member Or General Partner, Subsequent Distribution Amount, Excluding Incentive Distribution Amount of cash or stock or unit payment to a limited liability corporation managing member or limited partnership general partner, excluding payments for incentive distributions, after the end of the accounting period. General partner's incentive distribution rights 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 general partner's distributions Managing Member or General Partner, Subsequent Distribution Amount Partners' distributions Partners, Total Subsequent Distribution Amount Total amount of cash or stock or unit payment to LP partners earned during the applicable period. Antero Midstream Partners L.P. [Member] Antero Midstream Partners L.P. [Member] Antero Midstream Partners L.P. [Member] MarkWest Ohio Fractionation Company, L.L.C. [Member] MarkWest Ohio Fractionation Company, L.L.C. [Member] MarkWest Ohio Fractionation Company, L.L.C. [Member] Contribution of fixed assets to joint venture Contribution of Property Capacity Capacity Capacity Other income - related parties Related Party Transaction, Other Revenues from Transactions with Related Party Statement of Cash Flows [Abstract] Increase/(decrease) in cash, cash equivalents and restricted cash Cash and Cash Equivalents, Period Increase (Decrease) [Abstract] Operating activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Adjustments to reconcile net income to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Amortization of deferred financing costs Amortization of Debt Issuance Costs Depreciation and amortization Deferred income taxes Deferred Income Tax Expense (Benefit) Asset retirement expenditures Retirement Expenditures Expenditures incurred through the retirement of assets. Loss / (gain) on disposal of assets Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property Income from equity method investments Distributions from unconsolidated affiliates Proceeds from Equity Method Investment, Distribution Changes in: Increase (Decrease) in Operating Capital [Abstract] Current receivables Increase (Decrease) in Accounts Receivable Inventories Increase (Decrease) in Inventories Fair value of derivatives Increase (Decrease) in Derivative Assets and Liabilities Current accounts payable and accrued liabilities Increase (Decrease) in Accounts Payable and Accrued Liabilities Receivables from / liabilities to related parties Increase (Decrease) in Due from Related Parties, Current Prepaid other current assets from related parties Increase (decrease) in prepaid other current assets from related parties Increase (decrease) in prepaid other current assets from related parties Deferred revenue Increase (Decrease) in Deferred Revenue All other, net Other Operating Activities, Cash Flow Statement Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Investing activities: Net Cash Provided by (Used in) Investing Activities [Abstract] Additions to property, plant and equipment Payments to Acquire Property, Plant, and Equipment Acquisitions, net of cash acquired Payments to Acquire Businesses, Net of Cash Acquired Disposal of assets Proceeds from Sales of Assets, Investing Activities Investments - net related party loans Payments for (Proceeds from) Investments Investments in unconsolidated affiliates Distributions from unconsolidated affiliates - return of capital Proceeds from Equity Method Investment, Distribution, Return of Capital All other, net Payments for (Proceeds from) Other Investing Activities Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Long-term debt - borrowings Proceeds from Issuance of Long-term Debt Long-term debt - repayments Repayments of Long-term Debt Related party debt - borrowings Proceeds from Related Party Debt Related party debt - repayments Repayments of Related Party Debt Debt issuance costs Payments of Debt Issuance Costs Net proceeds from equity offerings Proceeds from Issuance or Sale of Equity Distributions to MPC for acquisitions Payments to Acquire Businesses and Equity Method Investments Payments to Acquire Businesses and Equity Method Investments Distributions to noncontrolling interests Payments to Noncontrolling Interests Distributions to preferred unitholders Payments of Distributions on Preferred Units Payments of Distributions on Preferred Units Distributions to unitholders and general partner Distribution Made to Limited Partner, Cash Distributions Paid Consideration payment to Class B unitholders Payments to Class B Unitholders Payments to Class B Unitholders All other, net Proceeds from (Payments for) Other Financing Activities Net cash provided by financing activities Net Cash Provided by (Used in) Financing Activities Net increase / (decrease) in cash, cash equivalents and restricted cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect Cash, cash equivalents and restricted cash at beginning of period Cash, cash equivalents and restricted cash at end of period Net income attributable to MPLX LP Net Income (Loss) Attributable to Parent Less: Preferred unit distributions 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. Less: General partner’s GP interest in net income attributable to MPLX LP Net Income (Loss) Allocated to General Partners New Accounting Pronouncements and Changes in Accounting Principles [Abstract] Accounting Standards New Accounting Pronouncements and Changes in Accounting Principles [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] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum [Member] Minimum [Member] Maximum [Member] Maximum [Member] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Fair Value, Inputs, Level 3 [Member] Fair Value, Inputs, Level 3 [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 Forward Commodity Price Fair Value Inputs Forward Commodity Price Represents the forward commodity price used as an input to measure fair value. Fair Value Inputs Probability of Renewal Fair Value Inputs Probability of Renewal Represents the percentage of likelihood of renewal of the commodity contract with embedded derivative. Fair Value Inputs 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. Statement of Financial Position [Abstract] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Wholly Owned Properties [Member] Wholly Owned Properties [Member] Property Subject to Operating Lease [Member] Property Subject to Operating Lease [Member] Partially Owned Properties [Member] Partially Owned Properties [Member] Refined Products [Member] Refined Products [Member] Refined Products [Member] Crude Oil [Member] Crude Oil [Member] Asset Class [Axis] Asset Class [Axis] Asset Class [Domain] Asset Class [Domain] Natural gas liquids storage caverns [Member] Natural gas liquids storage caverns [Member] Natural gas liquids storage caverns [Member] Light-product terminal [Member] Light-product terminal [Member] Light-product terminal [Member] MPLX Logistics LLC MPLX Logistics LLC [Member] MPLX Logistics LLC [Member] MPLX Holdings Inc MPLX Holdings Inc [Member] MPLX Holdings Inc [Member] HST & WHC & MPLXT HST & WHC & MPLXT [Member] HST & WHC & MPLXT [Member] General Partner Common Units General Partner Common Units [Member] General Partner Common Units [Member] Cash and Cash Equivalents [Member] Cash and Cash Equivalents [Member] Business Acquisition [Line Items] Business Acquisition [Line Items] Equity interest issued or issuable, value assigned Business Acquisition, Equity Interest Issued or Issuable, Value Assigned 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. Units acquired 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 Number of light product terminals Number of light product terminals Number of light product terminals Property, Plant and Equipment Property, Plant and Equipment Disclosure [Text Block] Investments and Noncontrolling Interests [Text Block] Equity Method Investments and Joint Ventures Disclosure [Text Block] Debt Disclosure [Abstract] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Line of Credit [Member] Line of Credit [Member] Senior Notes [Member] Senior Notes [Member] MPLX Revolver [Member] MPLX Revolver [Member] MPLX Revolving Credit Facility [Member] Bank revolving credit facility due 2022 MPLX Revolver due July 2022 [Member] MPLX Revolver due July 2022 Senior Notes Due March 2023 [Member] Senior Notes Due March 2023 [Member] Senior Notes Due March 2023 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] Senior Notes Due March 2028 [Member] Senior Notes Due March 2028 [Member] Senior Notes Due March 2028 Senior Notes Due April 2038 [Member] Senior Notes Due April 2038 [Member] Senior Notes Due April 2038 Senior Notes Due April 2048 [Member] Senior Notes Due April 2048 [Member] Senior Notes Due April 2048 Senior Notes Due April 2058 [Member] Senior Notes Due April 2058 [Member] Senior Notes Due April 2058 MPLX 364-Day Term Loan [Member] MPLX 364-Day Term Loan [Member] MPLX 364-Day Term Loan MPLX LP MPLX LP [Member] MPLX LP [Member] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Debt Instrument [Line Items] Debt Instrument [Line Items] Line of Credit Facility, Maximum Borrowing Capacity Line of Credit Facility, Maximum Borrowing Capacity Debt Instrument, Term Debt Instrument, Term Proceeds from Lines of Credit Proceeds from Long-term Lines of Credit Debt Instrument, Interest Rate, Effective Percentage Debt Instrument, Interest Rate, Effective Percentage Repayments of Long-term Lines of Credit Repayments of Long-term Lines of Credit Long-term debt, gross Long-term Debt, Gross Letters of Credit Outstanding Letters of Credit Outstanding, Amount Line of Credit Facility, Remaining Borrowing Capacity Line of Credit Facility, Remaining Borrowing Capacity Line of Credit Facility, Remaining Borrowing Capacity, Percentage Line of Credit Facility, Remaining Borrowing Capacity, Percentage Line of Credit Facility, Remaining Borrowing Capacity, Percentage Current borrowing capacity Line of Credit Facility, Current Borrowing Capacity Debt Instrument, Interest Rate, Stated Percentage Debt Instrument, Interest Rate, Stated Percentage Percent of Par Percent of Par Percent of Par Repayments of Short-term Debt Repayments of Short-term Debt Debt Instrument, Face Amount Debt Instrument, Face Amount Proceeds from new debt Proceeds from (Repayments of) Debt Fair Value Measurements Fair Value Disclosures [Text Block] Number of reportable segments Number of Reportable Segments Inventory Disclosure [Abstract] Inventories Inventory Disclosure [Text Block] Ozark Pipeline [Member] Ozark Pipeline [Member] Ozark Pipeline [Member] Pipeline length Pipeline length Pipeline length Pipeline diameter Pipeline diameter Pipeline diameter Pipeline barrels capable of transportation Pipeline Barrels Handled Pipeline Barrels Handled Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Other current assets [Member] Other Current Assets [Member] Other current liabilities [Member] Other Current Liabilities [Member] Other noncurrent assets [Member] Other Noncurrent Assets [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 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 Dividend rate, percentage Preferred Stock, Dividend Rate, Percentage Price per share Shares Issued, Price Per Share Issuance of redeemable preferred units Proceeds from Issuance of Preferred Limited Partners Units Dividend rate, per-dollar-amount Preferred Stock, Dividend Rate, Per-Dollar-Amount Distribution Made to Limited Partner, Declaration Date Distribution Made to Limited Partner, Distributions Declared, Per Unit Description Preferred Units, Description Equity Method Investments and Joint Ventures MPC Q3 Drops [Abstract] Equity Method Investments and Joint Ventures MPC Q3 Drops [Abstract] LOOP LOCAP SAX and Explorer Llc LOOP LOCAP SAX and Explorer Llc [Member] LOOP LOCAP SAX and Explorer Llc [Member] 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. 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. Number of pump stations Number of Pump Stations Number of Pump Stations Distributions of cash received from joint-interest acquisition entities to MPC Payments of Distributions to Affiliates Balance at December 31, 2017 Temporary Equity, Carrying Amount, Including Portion Attributable to Noncontrolling Interests Net income Temporary Equity, Net Income Balance at September 30, 2018 MarkWest [Member] MarkWest [Member] MarkWest [Member] Marathon Pipe Line LLC [Member] Marathon Pipe Line Llc [Member] Marathon pipe line Llc. Capital Lease Obligations [Member] Capital Lease Obligations [Member] 5.500% senior notes due February 2023 Senior Notes Due February 2023 [Member] Senior Notes Due February 2023 4.500% senior notes due July 2023 Senior Notes Due July 2023 [Member] Senior Notes Due July 2023 4.875% senior notes due December 2024 Senior Notes Due December 2024 [Member] Senior Notes Due December 2024 4.000% senior notes due February 2025 Senior Notes Due February 2025 [Member] Senior Notes Due February 2025 4.875% senior notes due June 2025 Senior Notes Due June 2025 [Member] Senior Notes Due June 2025 Expiration date Line of Credit Facility, Expiration Date Debt Instrument, Maturity Date Debt Instrument, Maturity Date Capital Lease Due Date Year Capital Lease Due Date Year The year in which the entity's capital leases are due, in CCYY format. Net Income Per Share [Table] Net Income Per Share [Table] Net Income Per Share [Table] Preferred Units Preferred Partner [Member] Net Income Per Share [Line Items] Net Income Per Share [Line Items] Net Income Per Share [Line Items] Potentially dilutive units Earnings Per Unit, Potentially Dilutive Units Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per unit (EPU) in the future that were not included in the computation of diluted EPU because to do so would have been antidilutive for the period presented. Less: Distribution declared Undistributed net loss attributable to MPLX LP Undistributed Earnings (Loss) Allocated to Participating Securities, Basic Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] 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 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 Terminals and related assets [Member] Terminals and related assets Refineries and related assets Refineries and related assets [Member] Refineries and related assets [Member] 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. Property, plant and equipment, gross Property, Plant and Equipment, Gross Less accumulated depreciation Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Property, plant and equipment, net Schedule of Stockholders Equity [Table Text Block] Schedule of Stockholders Equity [Table Text Block] Schedule Of Calculation Of Net Income Applicable to Partners [Table Text Block] 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 [Table Text Block] Distributions Made to Limited Partner, by Distribution [Table Text Block] Income Statement [Abstract] Interest costs capitalized Interest Costs Capitalized Purchased product costs Purchased product costs [Member] Purchased product costs [Member] Cost of revenues Cost of Sales [Member] Realized gain (loss) 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 gain (loss) Debt Debt Disclosure [Text Block] Description Of Business And Basis Of Presentation [Table] Description Of Business And Basis Of Presentation [Table] Description Of Business And Basis Of Presentation [Table] 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] Number of Units Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward] Outstanding at December 31, 2017 Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number Granted Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted Settled Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Exercised Forfeited Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Forfeitures Outstanding at September 30, 2018 Weighted Average Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments. Weighted Average Grant Fair Value [Roll Forward] Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments. Weighted Average Grant Fair Value [Roll Forward] Outstanding at December 31, 2017 Share Based Compensation Arrangement By Share Based Payment Award Non Option Equity Instruments Weighted Average Grant Date Fair Value Outstanding Share Based Compensation Arrangement By Share Based Payment Award Non Option Equity Instruments Weighted Average Grant Date Fair Value Outstanding Granted Settled Share Based Compensation Arrangement By Share Based Payment Award Non Option Equity Instruments Weighted Average Grant Date Fair Value Issued Share Based Compensation Arrangement By Share Based Payment Award Non Option Equity Instruments Weighted Average Grant Date Fair Value Issued Forfeited Share Based Compensation Arrangement By Share Based Payment Award Non Option Equity Instruments Weighted Average Grant Date Fair Value Forfeited Share Based Compensation Arrangement By Share Based Payment Award Non Option Equity Instruments Weighted Average Grant Date Fair Value Forfeited Outstanding at September 30, 2018 Contract assets, beginning balance Contract with Customer, Asset, Gross Contract assets, additions/(deletions) Contract with Customer, Asset Increase (Decrease) Contract with Customer, Asset Increase (Decrease) Contract assets, revenue recognized Contract with Customer, Asset, Reclassified to Receivable Contract assets, ending balance Deferred revenue, beginning balance Deferred Revenue, Current Deferred revenue, additions/(deletions) Deferred Revenue, Period Increase (Decrease) Deferred revenue, revenue recognized Deferred Revenue, Revenue Recognized Deferred revenue, ending balance Deferred revenue - related parties, beginning balance Deferred Revenue, Current, Related Parties The carrying amount of consideration received or receivable from related parties as of the balance sheet date on potential earnings that were not recognized as revenue in conformity with GAAP, and which are expected to be recognized as such within one year or the normal operating cycle, if longer, including sales, license fees, and royalties, but excluding interest income. Deferred revenue - related party, additions/(deletions) Deferred Revenue - Related Party, Period Increase (Decrease) Deferred Revenue - Related Party, Period Increase (Decrease) Deferred revenue - related parties, revenue recognized Deferred Revenue - Related Parties, Revenue Recognized Deferred Revenue - Related Parties, Revenue Recognized Deferred revenue - related parties, ending balance Long-term deferred revenue, beginning balance Long-term deferred revenue, additions/(deletions) Deferred Revenue, Noncurrent, Period Increase (Decrease) Deferred Revenue, Noncurrent, Period Increase (Decrease) Long-term deferred revenue, revenue recognized Deferred Revenue, Noncurrent, Revenue Recognized Deferred Revenue, Noncurrent, Revenue Recognized Long-term deferred revenue, ending balance Long-term deferred revenue - related parties, beginning balance Deferred Revenue, Noncurrent, Related Parties Amount of long-term deferred revenue from relate parties due after one year. Long-term deferred revenue - related party, additions/(deletions) Deferred Revenue, Noncurrent, Related Party, Period Increase (Decrease) Deferred Revenue, Noncurrent, Related Party, Period Increase (Decrease) Long-term deferred revenue - related parties, revenue recognized Deferred Revenue, Noncurrent, Related Parties, Revenue Recognized Deferred Revenue, Noncurrent, Related Parties, Revenue Recognized Long-term deferred revenue - related parties, ending balance Liability, change in timeframe, performance obligation satisfied, revenue recognized Contract with Customer, Liability, Change in Timeframe, Performance Obligation Satisfied, Revenue Recognized Commitments and Contingencies Disclosure [Text Block] Commitments and Contingencies Disclosure [Text Block] Gas Distribution [Member] Distribution Type [Domain] Storage Services Butane and Propane Caverns [Member] Storage Services Butane and Propane Caverns [Member] Storage Services Butane and Propane Caverns [Member] Storage Services Tank Farm [Member] Storage Services Tank Farm [Member] Storage Services Tank Farm [Member] Management Services Agreements [Member] Management Services Agreements [Member] Management Services Agreements [Member] Lease Arrangement, Type [Axis] Lease Arrangement, Type [Axis] Lease Arrangement, Type [Domain] Lease Arrangement, Type [Domain] Ten Year Storage Services Agreement [Member] Ten Year Storage Services Agreement [Member] Ten Year Storage Services Agreement [Member] Three Year Storage Services Agreement [Member] Three Year Storage Services Agreement [Member] Three Year Storage Services Agreement [Member] Lease Agreements [Member] Lease Agreements [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 [Member] Commercial Agreements [Member] Commercial Agreements [Member] Description of variable rate basis Debt Instrument, Description of Variable Rate Basis Proceeds from short-term debt Proceeds from Lines of Credit Repayments of short-term debt Repayments of Lines of Credit Intercompany loan outstanding Long-term Line of Credit Interest rate during period Line of Credit Facility, Interest Rate During Period Term Of Agreements Term Of Agreements Term Of Agreements Prepaid Insurance Prepaid Insurance Revenue from Related Parties Revenue from Related Parties Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Contract with customer, liability Contract with Customer, Liability Remaining performance obligation, expected timing of satisfaction, years Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period 2018 Revenue, Remaining Performance Obligation, Expected to be Recognized in Current Fiscal Year Revenue, Remaining Performance Obligation, Expected to be Recognized in Current Fiscal Year 2019 Revenue, Remaining Performance Obligation, Expected to be Recognized in Next Fiscal Year Revenue, Remaining Performance Obligation, Expected to be Recognized in Next Fiscal Year 2020 Revenue, Remaining Performance Obligation, Expected to be Recognized in Third Fiscal Year Revenue, Remaining Performance Obligation, Expected to be Recognized in Third Fiscal Year 2021 Revenue, Remaining Performance Obligation, Expected to be Recognized in Fourth Fiscal Year Revenue, Remaining Performance Obligation, Expected to be Recognized in Fourth Fiscal Year 2022 and thereafter Revenue, Remaining Performance Obligation, Expected to be Recognized in Fifth Fiscal Year and Thereafter Revenue, Remaining Performance Obligation, Expected to be Recognized in Fifth Fiscal Year and Thereafter Total revenue on remaining performance obligations Revenue, Remaining Performance Obligation, Amount Reconciliation of Other Significant Reconciling Items from Segments to Consolidated [Table] Reconciliation of Other Significant Reconciling Items from Segments to Consolidated [Table] Segment Reporting, Other Significant Reconciling Item [Line Items] Segment Reporting, Other Significant Reconciling Item [Line Items] Assets Assets 3.375% senior notes due March 2023 4.000% senior notes due March 2028 4.500% senior notes due April 2038 4.700% senior notes due April 2048 4.900% senior notes due April 2058 MarkWest - 4.500% - 5.500% senior notes, due 2023-2025 MarkWest Senior Notes [Member] MarkWest Senior Notes [Member] Capital lease obligations due 2020 Capital Lease Obligations Total Debt and Capital Lease Obligations Unamortized debt issuance costs Unamortized Debt Issuance Expense Unamortized discount Debt Instrument, Unamortized Discount Amounts due within one year Debt, Current Total long-term debt due after one year Long-term Debt and Capital Lease Obligations Expenses incurred under employee services agreements Labor and Related Expense Refining Logistics [Member] Refining Logistics [Member] Refining Logistics [Member] Fuels Distribution [Member] Fuels Distribution [Member] Fuels Distribution [Member] Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest Number of storage tanks Number of storage tanks Number of storage tanks Number of rail and truck racks Number of rail and truck racks Number of rail and truck racks Number of docks and gasoline blenders Number of docks and gasoline blenders Number of docks and gasoline blenders 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 Description of the Business and Basis of Presentation Business Description and Basis of Presentation [Text Block] 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. Total revenues and other income 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 General and administrative expenses General and Administrative Expense Other taxes Taxes, Miscellaneous Total costs and expenses Costs and Expenses Income from operations Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent 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 $9 million, $6 million, $27 million, and $24 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 for income taxes Income Tax Expense (Benefit) Net income Less: Net income (loss) attributable to noncontrolling interest 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 (loss) attributable to MPLX LP Limited partners' interest in net income (loss) attributable to MPLX LP Net Income (Loss) Allocated to Limited Partners Per Unit Data (See Note 7) Earnings Per Unit [Abstract] Net income (loss) attributable to MPLX LP per limited partner unit: Net Income (Loss), Per Outstanding Limited Partnership Unit, Basic, Net of Tax [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 Weighted average limited partner units outstanding: Limited Partners' Capital Account [Abstract] Common - basic (in shares) Weighted Average Limited Partnership Units Outstanding, Basic Common - diluted (in shares) Weighted Average Limited Partnership Units Outstanding, Diluted Reconciliation of Revenue from Segments to Consolidated [Table] Reconciliation of Revenue from Segments to Consolidated [Table] Segment Reconciling Items [Member] Segment Reconciling Items [Member] Segment Reporting, Revenue Reconciling Item [Line Items] Segment Reporting, Revenue Reconciling Item [Line Items] Income Tax Expense (Benefit) Amortization of Debt Issuance Costs Allocated Share-based Compensation Expense Allocated Share-based Compensation Expense Interest and Other Financial Costs Interest and Other Financial Costs Interest and Other Financial Costs Proceeds from Equity Method Investment, Distribution, Return of Capital Derivative Instruments Not Designated as Hedging Instruments, Unrealized Gain (Loss), Net Acquisition Costs, Period Cost Acquisition Costs, Period Cost Adjusted EBITDA attributable to noncontrolling interests Adjusted EBITDA attributable to noncontrolling interests Adjusted EBITDA attributable to noncontrolling interests Adjusted EBITDA attributable to Predecessor Adjusted EBITDA attributable to Predecessor Adjusted EBITDA attributable to Predecessor Net income Schedule of Cash and Cash Equivalents [Table Text Block] Schedule of Cash and Cash Equivalents [Table Text Block] Summary of Supplemental Cash Flow Information [Table Text Block] Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Summary 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] Schedule of Reconciliation of Additions to Property, Plant And Equipment to Total Capital Expenditures [Table Text Block] LOOP and Explorer Loop Llc and Explorer Pipeline [Member] Loop Llc and Explorer Pipeline [Member] Assets Assets [Abstract] Current assets: Assets, Current [Abstract] Receivables, net Accounts Receivable, Net, Current Receivables - related parties Accounts Receivable, Related Parties, Current Other current assets Other Assets, Current Total current assets Assets, Current Intangibles, net Intangible Assets, Net (Excluding Goodwill) Other noncurrent assets Other Assets, Noncurrent Total assets Liabilities Liabilities [Abstract] Current liabilities: Liabilities, Current [Abstract] Accounts payable Accounts Payable, Current Deferred revenue - related parties Accrued interest payable Interest Payable Other current liabilities Other Liabilities, Current Total current liabilities Liabilities, Current Long-term deferred revenue - related parties Long-term debt Deferred income taxes Deferred Tax Liabilities, Net, Noncurrent Deferred credits and other liabilities Deferred Credits and Other Liabilities, Noncurrent Total liabilities Liabilities Commitments and contingencies (see Note 20) Commitments and Contingencies Redeemable preferred units Equity Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Total MPLX LP partners’ capital Noncontrolling interests Partners' Capital Attributable to Noncontrolling Interest Total equity Total liabilities, preferred units and equity Liabilities and Equity Units issued Limited Partners' Capital Account, Units Issued Units outstanding Limited Partners' Capital Account, Units Outstanding GP units issued General Partners' Capital Account, Units Issued GP units outstanding General Partners' Capital Account, Units Outstanding 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. 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. Product sales to MPC that net to 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. Increase in capital accruals Increase Decrease In Capital Accruals Increase (Decrease) In Capital Accruals Net cash provided by operating activities included: Supplemental Cash Flow Information [Abstract] Interest paid (net of amounts capitalized) Interest Paid, Excluding Capitalized Interest, Operating Activities Income Taxes Paid, Net Income Taxes Paid, Net Non-cash investing and financing activities: Noncash Investing and Financing Items [Abstract] Net transfers of property, plant and equipment from materials and supplies inventories Non Cash Net Transfers Of Materials And Supplies Inventories Non cash net transfers of materials and supplies inventories. Business Acquisition, Pro Forma Information [Table Text Block] Business Acquisition, Pro Forma Information [Table 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. Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Fair Value Carrying Value by Balance Sheet Grouping [Table Text Block] Fair Value, by Balance Sheet Grouping [Table Text Block] Summary of Outstanding Borrowings Schedule of Debt [Table Text Block] 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] Limited Partners Subordinated Units [Member] Limited Partners Subordinated Units [Member] Limited Partners Subordinated Units [Member] 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 (loss) attributable to MPLX LP: Partnership Income [Abstract] Undistributed net income (loss) attributable to MPLX LP Undistributed Earnings (Loss) Available to Common Shareholders, Basic Weighted average units outstanding: Net Income (Loss), Per Outstanding Limited Partnership Unit, Basic, Other Disclosures [Abstract] Net income attributable to MPLX LP 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) 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] Reported Value Measurement [Member] Reported Value Measurement [Member] Estimate of Fair Value Measurement [Member] Estimate of Fair 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 Significant Accounting Policies Significant Accounting Policies [Text Block] Position [Axis] Position [Axis] Position [Domain] Position [Domain] Short Short [Member] Long Long [Member]