v3.3.0.814

Debt - Additional Information (Detail) - USD ($) $ in Millions			9 Months Ended
		Feb. 12, 2015	Sep. 30, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Unamortized Debt Issuance Expense	[1]		$ 4.1	$ 0.0
Marathon Pipe Line Llc [Member]
Debt Instrument [Line Items]
Capital Lease Due Date Year			2020
MPLX Pipe Line Holdings LP [Member] | Related Party Revolving Credit Agreement [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date			Mar. 31, 2019
Senior Notes Due Two Thousand Twenty Five [Member] | Mplx Lp [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 500.0
Debt Instrument, Interest Rate, Stated Percentage		4.00%
Debt Instrument, Maturity Date		Feb. 15, 2025	Feb. 15, 2025
Proceeds from (Repayments of) Debt			$ 495.0
MPLX Revolver [Member] | Mplx Lp [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Expiration Date			Nov. 20, 2019
Proceeds from Lines of Credit			$ 30.0
Debt Instrument, Interest Rate, Effective Percentage			1.457%
Extinguishment of Debt, Amount			$ 415.0
Letters of Credit Outstanding, Amount			0.0
Line of Credit Facility, Remaining Borrowing Capacity			$ 1,000.0
Line of Credit Facility, Remaining Borrowing Capacity, Percentage			100.00%
MPLX Term Loan [Member] | Mplx Lp [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date			Nov. 20, 2019
Debt Instrument, Interest Rate, Effective Percentage			1.651%
Line of Credit [Member] | MPLX Revolver [Member] | Mplx Lp [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 0.0	$ 385.0
Maximum [Member] | MPLX Term Loan [Member] | Mplx Lp [Member] | Letter of Credit [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity			$ 250.0
[1] (1) We adopted the updated FASB debt issuance cost standard as of June 30, 2015. This has been applied retrospectively and there was no effect to the prior period presented.

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- Definition

The year in which the entity's capital leases are due, in CCYY format.

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Line of Credit Facility, Remaining Borrowing Capacity, Percentage

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- Definition

Amount of long-term debt before deduction of unamortized discount or premium. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, with initial maturities beyond one year or the normal operating cycle, if longer.

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-Publisher FASB



-Name Accounting Standards Codification



-Topic 210



-SubTopic 10



-Section S99



-Paragraph 1



-Subparagraph (SX 210.5-02.22)



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- Definition

Face (par) amount of debt instrument at time of issuance.

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-SubTopic 30



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- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Contractual interest rate for funds borrowed, under the debt agreement.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

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- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

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- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

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Date the credit facility terminates, in CCYY-MM-DD format.

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- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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The cash inflow from a contractual arrangement with the lender, including letter of credit, standby letter of credit and revolving credit arrangements, under which borrowings can be made up to a specific amount at any point in time with maturities due beyond one year or the operating cycle, if longer.

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The net cash inflow or outflow in aggregate debt due to repayments and proceeds from additional borrowings.

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The cash outflow for the settlement of obligation drawn from a contractual arrangement with the lender, including letter of credit, standby letter of credit and revolving credit arrangements, under which borrowings can be made up to a specific amount at any point in time with maturities due beyond one year or the operating cycle, if longer.

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- Definition

The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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