Revenue from Contract with Customer [Abstract] Statement [Table] Statement [Table] Contract with Customer, Balance [Axis] Contract with Customer, Balance [Axis] Contract with Customer, Balance [Axis] Contract with Customer, Balance [Domain] Contract with Customer, Balance [Domain] [Domain] for Contract with Customer, Balance [Axis] 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] Statement [Line Items] Statement [Line Items] Contract assets, beginning balance Contract with Customer, Asset, before Allowance for Credit Loss 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 Deferred Revenue, Noncurrent 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 Accounting Policies [Abstract] Description Of Business And Basis Of Presentation [Table] Description Of Business And Basis Of Presentation [Table] Description Of Business And Basis Of Presentation [Table] Business Combination, Separately Recognized Transactions [Axis] Business Combination, Separately Recognized Transactions [Axis] Business Combination, Separately Recognized Transactions [Domain] Business Combination, Separately Recognized Transactions [Domain] ANDX LP [Member] ANDX LP [Member] ANDX LP [Member] Public or Nonpublic Designator [Axis] Public or Nonpublic Designator [Axis] Public or NonPublic Designator [Axis] Public or Non-Public Designator [Domain] Public or Non-Public Designator [Domain] [Domain] for Public or Non-Public Designator [Axis] Public Public [Member] Public [Member] Nonpublic [Member] Nonpublic [Member] Nonpublic [Member] Segments [Axis] Segments [Axis] Segments [Domain] Segments [Domain] 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 reportable segments Number of Reportable Segments Common Units Conversion Ratio - ANDX to MPLX Common Units Conversion Ratio - ANDX to MPLX Ratio applied to the conversion of ANDX common units to MPLX common units Accounting Changes and Error Corrections [Abstract] New Accounting Pronouncements or Change in Accounting Principle [Table] New Accounting Pronouncements or Change in Accounting Principle [Table] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Operating Lease Right Of Use Asset [Member] Operating Lease Right Of Use Asset [Member] Operating Lease Right Of Use Asset [Member] Operating Lease Liability [Member] Operating Lease Liability [Member] Operating Lease Liability [Member] Accounting Standards Update 2016-02 [Member] Accounting Standards Update 2016-02 [Member] New Accounting Pronouncements or Change in Accounting Principle [Line Items] New Accounting Pronouncements or Change in Accounting Principle [Line Items] New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification Equity [Abstract] Schedule of Stockholders Equity [Table Text Block] Schedule of Stockholders Equity [Table Text Block] Distributions Made to Limited Partner, by Distribution [Table Text Block] Distributions Made to Limited Partner, by Distribution [Table Text Block] Debt Disclosure [Abstract] Debt Debt Disclosure [Text Block] Supplemental Cash Flow Elements [Abstract] 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 Operating Lease, Payments Operating Lease, Payments Finance Lease, Interest Payment on Liability Finance Lease, Interest Expense Finance Lease, Principal Payments Finance Lease, Principal Payments 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. Sales-type Lease, Selling Profit (Loss) Sales-type Lease, Selling Profit (Loss) Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Right-of-Use Asset Obtained in Exchange for Finance Lease Liability Right-of-Use Asset Obtained in Exchange for Finance Lease Liability 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] Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] 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 [Line Items] Derivative [Line Items] 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) on Derivatives and Commodity Contracts Unrealized Gain (Loss) on Derivatives and Commodity Contracts Total gain (loss) Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event Subsequent Event [Member] Statistical Measurement [Axis] Statistical Measurement [Axis] Statistical Measurement [Domain] Statistical Measurement [Domain] Minimum [Member] Minimum [Member] Maximum [Member] Maximum [Member] Extinguishment of Debt [Axis] Extinguishment of Debt [Axis] Extinguishment of Debt, Type [Domain] Extinguishment of Debt, Type [Domain] Debt Premium [Member] Debt Premium [Member] Debt Premium [Member] 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] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] MPLX Revolving Credit Facility due July 2024 [Member] MPLX Revolving Credit Facility due July 2024 [Member] MPLX Revolving Credit Facility due July 2024 [Member] Bank revolving credit facility due 2022 MPLX Revolver due July 2022 [Member] MPLX Revolver due July 2022 Senior Notes Due October 2019 [Member] Senior Notes Due October 2019 [Member] Senior Notes Due October 2019 [Member] Senior Notes Due December 2022 [Member] Senior Notes Due December 2022 [Member] Senior Notes Due December 2022 [Member] Senior Notes Due October 2022 [Member] Senior Notes Due October 2022 [Member] Senior Notes Due October 2022 [Member] Senior Notes Due May 2024 [Member] Senior Notes Due May 2024 [Member] Senior Notes Due May 2024 [Member] Senior Notes Due January 2025 [Member] Senior Notes Due January 2025 [Member] Senior Notes Due January 2025 [Member] Senior Notes Due December 2027 [Member] Senior Notes Due December 2027 [Member] Senior Notes Due December 2027 [Member] Senior Notes Due December 2047 [Member] Senior Notes Due December 2047 [Member] Senior Notes Due December 2047 [Member] Senior Notes Due February 2023 [Member] Senior Notes Due February 2023 [Member] Senior Notes Due February 2023 Senior Notes Due February 2029 [Member] Senior Notes Due February 2029 [Member] Senior Notes Due February 2029 [Member] Senior Notes Due February 2049 [Member] Senior Notes Due February 2049 [Member] Senior Notes Due February 2049 [Member] Senior Notes Due March 2023 [Member] Senior Notes Due March 2023 [Member] Senior Notes Due March 2023 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 ANDX Bank Revolving Credit Facilities [Member] ANDX Bank Revolving Credit Facilities [Member] ANDX Bank Revolving Credit Facilities MPLX Term Loan [Member] MPLX Term Loan [Member] MPLX Term Loan [Member] Floating Rate Senior Notes Due September 2021 [Member] Floating Rate Senior Notes Due September 2021 [Member] Floating Rate Senior Notes Due September 2021 [Member] Floating Rate Senior Notes Due September 2022 [Member] Floating Rate Senior Notes Due September 2022 [Member] Floating Rate Senior Notes Due September 2022 [Member] MPLX LP MPLX LP [Member] MPLX LP [Member] Andeavor Logistics [Member] Andeavor Logistics [Member] Andeavor Logistics [Member] MarkWest [Member] MarkWest [Member] MarkWest [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 Line of Credit Facility, Current Borrowing Capacity Line of Credit Facility, Current Borrowing Capacity Debt Instrument, Description of Variable Rate Basis Debt Instrument, Description of Variable Rate Basis Long-term Debt, Maturity Date Long-term Debt, Maturity Date Long-term Line of Credit Long-term Line of Credit Debt Instrument, Interest Rate, Stated Percentage Debt Instrument, Interest Rate, Stated Percentage Repayments of Long-term Debt Repayments of Long-term Debt Interest Expense, Long-term Debt Interest Costs Incurred Percent of Par Percent of Par Percent of Par Extinguishment of Debt, Gain (Loss), Net of Tax Extinguishment of Debt, Gain (Loss), Net of Tax Repayments of Short-term Debt Repayments of Short-term Debt Number Of Prior Quarterly Reporting Periods Covenant Number Of Prior Quarterly Reporting Periods Covenant Number Of Prior Quarterly Reporting Periods Covenant Covenant Ratio Debt To Ebitda Covenant Ratio Debt To Ebitda Covenant Ratio Debt To Ebitda Covenant Ratio Debt To Ebitda Post Acquisition Covenant Ratio Debt To Ebitda Post Acquisition Covenant Ratio Debt To Ebitda Post Acquisition Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] L&S Logistics and Storage [Member] Logistics and Storage [Member] G&P Gathering and Processing [Member] Gathering and Processing [Member] 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 2022 Revenue, Remaining Performance Obligation, Expected to be Recognized in Fourth Fiscal Year Revenue, Remaining Performance Obligation, Expected to be Recognized in Fourth Fiscal Year 2023 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 Share-based Payment Arrangement [Abstract] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Award Type [Axis] Award Type [Axis] Award Type [Domain] Award Type [Domain] Performance Shares [Member] Performance Shares [Member] Performance Units Market Condition [Member] Performance Units Market Condition [Member] Performance Units Market Condition [Member] Grant date fair value based on market conditions Performance Unit Performance Condition [Member] Performance Unit Performance Condition [Member] Performance Unit Performance Condition [Member] Grant date fair value of the performance condition Equity Transactions And Share Based Compensation [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] 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 Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Outstanding at December 31, 2018 Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Granted Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Settled Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Forfeited Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Outstanding at September 30, 2019 Related Party Transactions [Abstract] Other Long-term Debt, Noncurrent Schedule of Long-term Debt Instruments [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] 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 Related Party Transactions [Table Text Block] Schedule of Related Party Transactions [Table Text Block] 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. 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] Earnings Per Share [Abstract] Net Income Per Share [Table] Net Income Per Share [Table] Net Income Per Share [Table] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] Series A Preferred Stock [Member] Series A Preferred Stock [Member] Series B Preferred Stock [Member] Series B Preferred Stock [Member] Related Party [Axis] Related Party [Axis] Related Party [Domain] Related Party [Domain] MPC Marathon Petroleum Corporation [Member] Marathon petroleum corporation. Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Partner Type [Axis] Partner Type [Axis] Partner Type of Partners' Capital Account, Name [Domain] Partner Type of Partners' Capital Account, Name [Domain] Series A Preferred Stock [Member] Preferred Partner [Member] Limited Partners Common Units Limited Partners Common Units [Member] Limited Partners Common Units [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. Net income attributable to MPLX LP Net Income (Loss) Attributable to Parent Less: Distribution declared Distribution Made to Limited Partner, Cash Distributions Declared Undistributed net income (loss) attributable to MPLX LP Undistributed Earnings (Loss) Available to Common Shareholders, Basic Undistributed net loss attributable to MPLX LP Undistributed Earnings (Loss) Allocated to Participating Securities, Basic Contributions from: Capital Contribution By Related Party Capital Contribution By Related Party Business Combinations [Abstract] Acquisitions Business Combination Disclosure [Text Block] Property, Plant and Equipment [Abstract] Property, Plant and Equipment Property, Plant and Equipment Disclosure [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] Schedule of Related Party Transactions, by Related Party [Table] Schedule of Related Party Transactions, by Related Party [Table] Investment, Name [Axis] Investment, Name [Axis] Investment, Name [Domain] Investment, Name [Domain] Related Party Transaction [Line Items] Related Party Transaction [Line Items] Related Party Transaction, Purchases from Related Party Related Party Transaction, Purchases from Related Party Revenue from Related Parties Revenue from Related Parties Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Text Block] Commitments and Contingencies Disclosure [Text Block] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Restatement [Axis] Restatement [Axis] Restatement [Domain] Restatement [Domain] Previously Reported [Member] Previously Reported [Member] Restatement Adjustment [Member] Restatement Adjustment [Member] LOOP and Explorer Loop Llc and Explorer Pipeline [Member] Loop Llc and Explorer Pipeline [Member] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Retained Earnings [Member] Retained Earnings [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] 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 Contracts [Member] Customer Contracts [Member] Ownership [Axis] Ownership [Axis] Ownership [Domain] Ownership [Domain] Business Acquisition [Line Items] Business Acquisition [Line Items] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Receivables, net Accounts Receivable, after Allowance for Credit Loss, Current Current Assets, Related Parties Current Assets, Related Parties Current Assets, Related Parties Inventories Inventory, Gross Other current assets Other Assets, Current Assets, Current Assets, Current Equity method investments Equity Method Investments Property, plant and equipment, net Property, Plant and Equipment, Net Intangibles, net Intangible Assets, Net (Excluding Goodwill) Other noncurrent assets Other Assets, Noncurrent Assets Assets Accounts payable Accounts Payable, Current Accrued Liabilities, Current Accrued Liabilities, Current Current Liabilities, Related Parties Current Liabilities, Related Parties Other Current Liabilities, Related Parties Accrued Property Plant and Equipment Current Accrued Property Plant and Equipment Current Carrying value as of the balance sheet date of obligations incurred through that date and payable for property, plant and equipment. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer). Accrued interest payable Interest Payable Other current liabilities Other Liabilities, Current Liabilities, Current Liabilities, Current Long-term deferred revenue Liabilities, Related Parties, Noncurrent Liabilities, Related Parties, Noncurrent Other Liabilities, Related Parties, Noncurrent Long-term debt Long-term Debt and Lease Obligation Deferred income taxes Deferred Tax Liabilities, Net, Noncurrent Deferred credits and other liabilities Deferred Credits and Other Liabilities, Noncurrent Liabilities Liabilities Series A preferred units Temporary Equity, Carrying Amount, Including Portion Attributable to Noncontrolling Interests Total MPLX LP partners’ capital Partners' Capital Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Revenues Revenues Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other Business Combination, Recognized Identifiable Assets Acquired, Equity Method Investments Business Combination, Recognized Identifiable Assets Acquired, Equity Method Investments Business Combination, Recognized Identifiable Assets Acquired, Equity Method Investments 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 Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill Finite-Lived Intangible Asset, Useful Life Finite-Lived Intangible Asset, Useful Life Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net Goodwill Goodwill Other Assets, Related Parties, Noncurrent Other Assets, Related Parties, Noncurrent Other Assets, Related Parties, Noncurrent Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest Net Income (Loss) Attributable to Parent Acquisition Costs, Period Cost Acquisition Costs, Period Cost Noncontrolling interests Partners' Capital Attributable to Noncontrolling Interest Partners' Capital, Including Portion Attributable to Noncontrolling Interest Partners' Capital, Including Portion Attributable to Noncontrolling Interest Liabilities and Equity Liabilities and Equity Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Income Statement [Abstract] Product and Service [Axis] Product and Service [Axis] Product and Service [Domain] Product and Service [Domain] Service [Member] Service [Member] Service, Other [Member] Service, Other [Member] Product [Member] Product [Member] Oil and Gas, Refining and Marketing [Member] Oil and Gas, Refining and Marketing [Member] Natural Gas, Midstream [Member] Natural Gas, Midstream [Member] Preferred Partner [Member] Revenues and other income: Revenues And Other Income [Abstract] Revenues and Other Income [Abstract] 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 Rental income Operating Leases, Income Statement, Lease Revenue 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. Income from equity method investments Income (Loss) from Equity Method Investments Other income Other Operating Income Other income - related parties Related Party Transaction, Other Revenues from Transactions with Related Party Costs and expenses: Costs and Expenses [Abstract] Cost of Goods and Services Sold Cost of Goods and Services Sold 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 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 $13 million, $9 million, $36 million and $27 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 Income (Loss) Attributable to Predecessor Income (Loss) Attributable to Predecessor Income (Loss) Attributable to Predecessor Net income (loss) attributable to MPLX LP Dividends, Preferred Stock Dividends, Preferred Stock Limited partners' interest in net income (loss) attributable to MPLX LP Net Income (Loss) Allocated to Limited Partners Per Unit Data (See Note 6) 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 Inventory Disclosure [Abstract] Inventories Inventory Disclosure [Text Block] Segment Reporting [Abstract] Segment Reporting Disclosure [Text Block] Segment Reporting Disclosure [Text Block] Related Party Revolving Credit Agreement [Member] Related Party Revolving Credit Agreement [Member] Related Party Revolving Credit Agreement [Member] MPC Investment [Member] MPC Investment [Member] MPC Investment [Member] Related Party Transaction [Axis] Related Party Transaction [Axis] Related Party Transaction [Domain] Related Party Transaction [Domain] Proceeds from Lines of Credit Proceeds from Lines of Credit Line of Credit Facility, Interest Rate During Period Line of Credit Facility, Interest Rate During Period Repayments of Lines of Credit Repayments of Lines of Credit Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Customer [Axis] Customer [Axis] Customer [Domain] Customer [Domain] Third Party [Member] Third Party [Member] Third Party [Member] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Operating Segments Operating Segments [Member] Segment Reconciling Items [Member] Segment Reconciling Items [Member] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Adjusted EBITDA attributable to Predecessor Adjusted EBITDA attributable to Predecessor Adjusted EBITDA attributable to Predecessor Other income Total segment revenues and 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] Disposal Group Classification [Axis] Disposal Group Classification [Axis] Disposal Group Classification [Domain] Disposal Group Classification [Domain] Schedule of Equity Method Investments [Line Items] Schedule of Equity Method Investments [Line Items] 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] 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] 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] 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) Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] 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] Statement of Cash Flows [Abstract] Payments of Distributions on Preferred Units from Predecessor Payments of Distributions on Preferred Units from Predecessor Payments of Distributions on Preferred Units from Predecessor Proceeds from Contributions from Parent Proceeds from Contributions from Parent 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 Deferred income taxes Deferred Income Tax Expense (Benefit) Asset retirement expenditures Retirement Expenditures Expenditures incurred through the retirement of assets. (Gain)/loss 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 Current assets/current liabilities - related parties Increase (Decrease) in Due from Related Parties, Current Increase (Decrease) in Other Operating Assets and Liabilities, Net Increase (Decrease) in Other Operating Assets and Liabilities, Net 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 Proceeds from Contributions from Affiliates Proceeds from Contributions from Affiliates Acquisitions, net of cash acquired Payments to Acquire Businesses, Net of Cash Acquired Disposal of assets Proceeds from Sales of Assets, Investing Activities Investments in unconsolidated affiliates Payments to Acquire Equity Method Investments 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 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 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 Contributions from noncontrolling interests Proceeds from Noncontrolling Interests All other, net Proceeds from (Payments for) Other Financing Activities Net cash used in financing activities Net Cash Provided by (Used in) Financing Activities Net (decrease)/increase 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, Restricted Cash and Restricted Cash Equivalents Cash, cash equivalents and restricted cash at end of period Leases [Abstract] Lessor, Lease, Description [Table] Lessor, Lease, Description [Table] Lease Arrangement, Type [Axis] Lease Arrangement, Type [Axis] Lease Arrangement, Type [Domain] Lease Arrangement, Type [Domain] Related Party [Member] Related Party [Member] Related Party [Member] Lessor, Lease, Description [Line Items] Lessor, Lease, Description [Line Items] Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Current Year Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Current Year Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Current Year Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Next Twelve Months Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Next Twelve Months Operating Leases, Future Minimum Payments Receivable, Current Operating Leases, Future Minimum Payments Receivable, Current Operating Leases, Future Minimum Payments Receivable, in Two Years Operating Leases, Future Minimum Payments Receivable, in Two Years Operating Leases, Future Minimum Payments Receivable, in Three Years Operating Leases, Future Minimum Payments Receivable, in Three Years Operating Leases, Future Minimum Payments Receivable, in Four Years Operating Leases, Future Minimum Payments Receivable, in Four Years Operating Leases, Future Minimum Payments Receivable, in Five Years Operating Leases, Future Minimum Payments Receivable, in Five Years Operating Leases, Future Minimum Payments Receivable, Thereafter Operating Leases, Future Minimum Payments Receivable, Thereafter Operating Leases, Future Minimum Payments Receivable Operating Leases, Future Minimum Payments Receivable Lessor, Operating Lease, Payments to be Received, Remainder of Fiscal Year Lessor, Operating Lease, Payments to be Received, Remainder of Fiscal Year Lessor, Operating Lease, Payments to be Received, Next Twelve Months Lessor, Operating Lease, Payments to be Received, Next Twelve Months Lessor, Operating Lease, Payments to be Received, Two Years Lessor, Operating Lease, Payments to be Received, Two Years Lessor, Operating Lease, Payments to be Received, Three Years Lessor, Operating Lease, Payments to be Received, Three Years Lessor, Operating Lease, Payments to be Received, Four Years Lessor, Operating Lease, Payments to be Received, Four Years Lessor, Operating Lease, Payments to be Received, Thereafter Lessor, Operating Lease, Payments to be Received, Thereafter Lessor, Operating Lease, Payments to be Received Lessor, Operating Lease, Payments to be Received Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Three Years Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Two Years Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Three Years Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Three Years Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Four Years Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Four Years Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Thereafter Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Thereafter Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received Sales-type and Direct Financing Leases, Lease Receivable, Undiscounted Excess Amount Sales-type and Direct Financing Leases, Lease Receivable, Undiscounted Excess Amount Sales-type Lease, Lease Receivable Sales-type Lease, Lease Receivable 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] Other Comprehensive Income (Loss), Net of Tax Other Comprehensive Income (Loss), Net of Tax Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] 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] Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] 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 Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net Schedule of Incentive Distribution Made to Managing Member or General Partner [Table] Schedule of Incentive Distribution Made to Managing Member or General Partner [Table] Preferred Units Preferred Class A [Member] Preferred Class B [Member] Preferred Class B [Member] Incentive Distribution Made to Managing Member or General Partner [Line Items] Incentive Distribution Made to Managing Member or General Partner [Line Items] Preferred Units, Outstanding Preferred Units, Outstanding Declaration date Distribution Made to Limited Partner, Declaration Date Distributions declared (including IDRs) 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 Partners, Total Subsequent Distribution Amount Partners, Total Subsequent Distribution Amount Total amount of cash or stock or unit payment to LP partners earned during the applicable period. Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders 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 Comprehensive Income (loss), Net of Tax, 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 Deferred Revenue Arrangement Type [Axis] Deferred Revenue Arrangement Type [Axis] Deferred Revenue [Domain] Deferred Revenue [Domain] Minimum Committed Volume Contracts [Member] Minimum Committed Volume Contracts [Member] Minimum Committed Volume Contracts [Member] Reimbursable Projects [Member] Reimbursable Projects [Member] Reimbursable Projects [Member] Other Noncurrent Liabilities [Member] Other Current Liabilities [Member] Other Noncurrent Liabilities [Member] Other Noncurrent Liabilities [Member] Other Affiliates [Member] Other Affiliates [Member] Receivables - related parties Accounts Receivable, Related Parties, Current Prepaid Insurance Prepaid Insurance Sales-type Lease, Interest Income Net Investment in Lease, Current Sales-type Lease, Unguaranteed Residual Asset Sales-type Lease, Unguaranteed Residual Asset Due from Related Parties, Noncurrent Due from Related Parties, Noncurrent Operating Lease, Right-of-Use Asset Operating Lease, Right-of-Use Asset Net Investment in Lease, Noncurrent Net Investment in Lease, Noncurrent Due to Related Parties, Current Due to Related Parties, Current Operating Lease, Liability, Current Operating Lease, Liability, Current Deferred Revenue Related Parties Deferred Revenue Related Parties Deferred revenue with related parties, including both current and non current portions. Operating Lease, Liability, Noncurrent Operating Lease, Liability, Noncurrent Deferred Revenue, Noncurrent, Related Parties Interest Costs Capitalized Interest Costs Capitalized New Accounting Pronouncements and Changes in Accounting Principles [Abstract] Accounting Standards New Accounting Pronouncements and Changes in Accounting Principles [Text Block] Description of New Accounting Pronouncements Not yet Adopted [Text Block] Description of New Accounting Pronouncements Not yet Adopted [Text Block] Business Description and Basis of Presentation [Text Block] Business Description and Basis of Presentation [Text Block] Lessor Disclosure [Abstract] Lessor, Operating Lease, Payments to be Received, Maturity [Table Text Block] Lessor, Operating Lease, Payments to be Received, Maturity [Table Text Block] Schedule of Property Subject to or Available for Operating Lease [Table Text Block] Schedule of Property Subject to or Available for Operating Lease [Table Text Block] Schedule of Future Minimum Rental Payments Receivable for Operating Leases [Table Text Block] Schedule of Future Minimum Rental Payments Receivable for Operating Leases [Table Text Block] Tabular disclosure of future minimum payments receivable in the aggregate and for each of the five succeeding fiscal years for operating leases having initial or remaining noncancelable lease terms in excess of one year. Temporary Equity 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 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 Partners' Capital Account, Units, Converted Partners' Capital Account, Units, Converted Partners' Capital Account, Units Partners' Capital Account, Units 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] Title of Individual [Domain] Title of Individual [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. Equity Transactions And Share Based Compensation [Line Items] Equity Transactions And Share Based Compensation [Line Items] Equity Transactions And Share Based Compensation [Line Items] 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 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 Share Based Compensation Arrangement By Share Based Payment Award Percentage Paid Out In Stock 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 Goodwill, Purchase Accounting Adjustments Goodwill, Purchase Accounting Adjustments (Decrease)/increase in capital accruals Increase Decrease In Capital Accruals Increase (Decrease) In Capital Accruals Commitments And Contingencies [Table] Commitments And Contingencies [Table] Commitments And Contingencies [Table] Guarantor Obligations, Nature [Axis] Guarantor Obligations, Nature [Axis] Guarantor Obligations, Nature [Domain] Guarantor Obligations, Nature [Domain] Guarantee Type, Other [Member] Guarantee Type, Other [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 Indirect Ownership Interest [Member] Indirect Ownership Interest [Member] Indirect Ownership Interest Bakken Pipeline System [Member] Bakken Pipeline System [Member] Bakken Pipeline System [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 Loss Contingency, Damages Sought, Value Loss Contingency, Damages Sought, Value Apex litigation settlement amount Litigation Settlement, Amount Awarded to Other Party Equity method investment, ownership percentage Equity Method Investment, Ownership Percentage Guarantor Obligations, Maximum Exposure, Undiscounted Guarantor Obligations, Maximum Exposure, Undiscounted Contractual commitments to acquire property, plant and equipment Purchase Commitment, Remaining Minimum Amount Committed Purchase Obligation Purchase Obligation Investments and Noncontrolling Interests [Text Block] Equity Method Investments and Joint Ventures Disclosure [Text Block] 3.375% senior notes due March 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 4.125% senior notes due March 2027 Senior Notes Due March 2027 [Member] Senior Notes Due March 2027 [Member] 4.000% senior notes due March 2028 4.500% senior notes due April 2038 5.200% senior notes due March 2047 Senior Notes Due March 2047 [Member] Senior Notes Due March 2047 [Member] 4.700% senior notes due April 2048 4.900% senior notes due April 2058 MarkWest - 4.500% - 4.875% senior notes, due 2023-2025 MarkWest Senior Notes [Member] MarkWest Senior Notes [Member] Finance Lease [Member] Finance Lease [Member] Finance Lease [Member] Marathon Pipe Line LLC [Member] Marathon Pipe Line Llc [Member] Marathon pipe line Llc. Financing lease obligations(1) Finance Lease, Liability Total Debt and Lease Obligation Unamortized debt issuance costs Unamortized Debt Issuance Expense Unamortized discount/premium Debt Instrument, Unamortized Discount Amounts due within one year Debt, Current Total long-term debt due after one year Derivative Instruments and Hedging Activities Disclosure [Text Block] Derivative Instruments and Hedging Activities Disclosure [Text Block] Net Income Per Limited Partner Unit Earnings Per Share [Text Block] Phantom Units Phantom Share Units (PSUs) [Member] Number of Units Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward] Outstanding at December 31, 2018 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, 2019 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, 2018 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, 2019 Equity Stockholders' Equity Note Disclosure [Text Block] 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] Lessee Maturity Table [Abstract] Lessee Maturity Table [Abstract] Lessee, Lease, Description [Table] Lessee, Lease, Description [Table] Lessee, Lease, Description [Line Items] Lessee, Lease, Description [Line Items] Operating Leases, Future Minimum Payments Due, Next Twelve Months Operating Leases, Future Minimum Payments Due, Next Twelve Months Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year Finance Lease, Liability, Payments, Remainder of Fiscal Year Finance Lease, Liability, Payments, Remainder of Fiscal Year Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months Finance Lease, Liability, Payments, Due Next Twelve Months Finance Lease, Liability, Payments, Due Next Twelve Months Finance Lease, Liability, Payments, Due Next Twelve Months Capital Leases, Future Minimum Payments Due, Next Twelve Months Operating Leases, Future Minimum Payments, Due in Two Years Operating Leases, Future Minimum Payments, Due in Two Years Lessee, Operating Lease, Liability, Payments, Due Year Two Lessee, Operating Lease, Liability, Payments, Due Year Two Finance Lease, Liability, Payments, Due Year Two Finance Lease, Liability, Payments, Due Year Two Finance Lease, Liability, Payments, Due Year Two Capital Leases, Future Minimum Payments Due in Two Years Operating Leases, Future Minimum Payments, Due in Three Years Operating Leases, Future Minimum Payments, Due in Three Years Lessee, Operating Lease, Liability, Payments, Due Year Three Lessee, Operating Lease, Liability, Payments, Due Year Three Finance Lease, Liability, Payments, Due Year Three Finance Lease, Liability, Payments, Due Year Three Finance Lease, Liability, Payments, Due Year Three Capital Leases, Future Minimum Payments Due in Three Years Operating Leases, Future Minimum Payments, Due in Four Years Operating Leases, Future Minimum Payments, Due in Four Years Lessee, Operating Lease, Liability, Payments, Due Year Four Lessee, Operating Lease, Liability, Payments, Due Year Four Finance Lease, Liability, Payments, Due Year Four Finance Lease, Liability, Payments, Due Year Four Finance Lease, Liability, Payments, Due Year Four Capital Leases, Future Minimum Payments Due in Four Years Operating Leases, Future Minimum Payments, Due in Five Years Operating Leases, Future Minimum Payments, Due in Five Years Lessee, Operating Lease, Liability, Payments, Due after Year Five Lessee, Operating Lease, Liability, Payments, Due after Year Five Finance Lease, Liability, Payments, Due after Year Five Finance Lease, Liability, Payments, Due after Year Five Finance Lease, Liability, Payments, Due after Year Five Capital Leases, Future Minimum Payments Due Thereafter Operating Leases, Future Minimum Payments Due Operating Leases, Future Minimum Payments Due Lessee, Operating Lease, Liability, Payments, Due Lessee, Operating Lease, Liability, Payments, Due Finance Lease, Liability, Payment, Due Finance Lease, Liability, Payment, Due Finance Lease, Liability, Payments, Due Capital Leases, Future Minimum Payments Due Lessee, Operating Lease, Liability, Undiscounted Excess Amount Lessee, Operating Lease, Liability, Undiscounted Excess Amount Finance Lease, Interest Payment on Liability Finance Lease, Interest Payment on Liability Finance Lease, Interest Payment on Liability Capital Leases, Future Minimum Payments, Interest Included in Payments Operating Lease, Liability Operating Lease, Liability Finance Lease, Liability Capital Leases, Future Minimum Payments, Present Value of Net Minimum Payments Finance Lease, Liability, Payments, Due Year Five Capital Leases, Future Minimum Payments Due in Five Years Operating Leases, Future Minimum Payments, Due Thereafter Operating Leases, Future Minimum Payments, Due Thereafter Finance Lease, Liability Major Property Class [Axis] Major Property Class [Axis] Major Property Class [Domain] Major Property Class [Domain] 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 Subject to or Available for Operating Lease, Gross Property Subject to or Available for Operating Lease, Gross Property Subject to or Available for Operating Lease, Accumulated Depreciation Property Subject to or Available for Operating Lease, Accumulated Depreciation Property Subject to or Available for Operating Lease, Net Property Subject to or Available for Operating Lease, Net Related Party Agreements and Transactions Related Party Transactions Disclosure [Text Block] Property, Plant and Equipment, Additions Property, Plant and Equipment, Additions 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. 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] Document And Entity Information [Abstract] Document and Entity Information [Abstract] Entities [Table] Entities [Table] Entity Listings, Exchange [Axis] Entity Listings, Exchange [Axis] Exchange [Domain] Exchange [Domain] General Partner Units General Partner Units [Member] General Partner Units [Member] Document Information [Line Items] Document Information [Line Items] Document Transition Report Document Transition Report Document Quarterly Report Document Quarterly Report Title of 12(b) Security Title of 12(b) Security Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Document Type Document Type Document Period End Date Document Period End Date Amendment Flag Amendment Flag Entity File Number Entity File Number 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 Filer Category Entity Filer Category Entity Emerging Growth Company Entity Emerging Growth Company Entity Small Business Entity Small Business Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Entity Address, Address Line One Entity Address, Address Line One Entity Address, City or Town Entity Address, City or Town Entity Address, State or Province Entity Address, State or Province Entity Address, Postal Zip Code Entity Address, Postal Zip Code City Area Code City Area Code Local Phone Number Local Phone Number Entity Current Reporting Status Entity Current Reporting Status Entity Interactive Data Current Entity Interactive Data Current Entity Shell Company Entity Shell Company Security Exchange Name Security Exchange Name Entity Tax Identification Number Entity Tax Identification Number Lessee Disclosure [Abstract] Lease, Cost [Table Text Block] Lease, Cost [Table Text Block] Supplemental Balance Sheet Disclosures [Text Block] Supplemental Balance Sheet Disclosures [Text Block] Schedule of Future Minimum Lease Payments for Operating and Finance Leases [Table Text Block] Schedule of Future Minimum Lease Payments for Operating and Finance Leases [Table Text Block] Schedule of Future Minimum Lease Payments for Operating and Finance Leases [Table Text Block] Restricted cash Restricted Cash Cash, cash equivalents and restricted cash Fair Value Measurements Fair Value Disclosures [Text Block] Summary of Inventories Schedule of Inventory, Current [Table Text Block] Line of Credit Facility, Expiration Date Line of Credit Facility, Expiration Date Debt Instrument, Maturity Date Debt Instrument, Maturity Date Capital Lease Due Date Year Finance Lease Due Date Year Finance Lease Due Date Year Use of Estimates, Policy [Policy Text Block] Use of Estimates, Policy [Policy Text Block] Earnings Per Share, Policy [Policy Text Block] Earnings Per Share, Policy [Policy Text Block] 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] Redeemable Preferred Units Temporary Equity Disclosure [Text Block] Temporary Equity Disclosure [Text Block] Statement of Stockholders' Equity [Abstract] General Partner General Partner [Member] Accumulated Other Comprehensive Loss AOCI Attributable to Parent [Member] Noncontrolling Interests Noncontrolling Interest [Member] Equity of Predecessor Limited Partners Class B Units [Member] Limited Partners Class B Units [Member] Limited Partners Class B Units [Member] Beginning Balance Distributions to: 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 MPC for acquisition Partners' Capital Account, Acquisitions Unitholders and general partner Partners' Capital Account, Distributions Noncontrolling interests Contributions from noncontrolling interests Partners' Capital Account, Exchanges and Conversions Partners' Capital Account, Exchanges and Conversions Other Stockholders' Equity, Other Ending Balance 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 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] Commodity contracts Embedded derivatives in commodity contracts 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. 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. Rollforward of Redeemable Preferred Units Temporary Equity [Table Text Block] Revenue from Contract with Customer [Text Block] Revenue from Contract with Customer [Text Block] Statement of Financial Position [Abstract] Assets Assets [Abstract] Current assets: Assets, Current [Abstract] Total current assets Total assets Liabilities Liabilities [Abstract] Current liabilities: Liabilities, Current [Abstract] Total current liabilities Total liabilities Commitments and contingencies (see Note 20) Commitments and Contingencies Equity Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]