Related Party Agreements and Transactions - Additional Information (Detail) $ in Millions	6 Months Ended	12 Months Ended
Jun. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)
Centennial [Member] \| MPC
Related Party Transaction [Line Items]
Equity Method Investment, Ownership Percentage	50.00%
Muskegon [Member] \| MPC
Related Party Transaction [Line Items]
Equity Method Investment, Ownership Percentage	60.00%
MarkWest Utica EMG [Member]
Related Party Transaction [Line Items]
Equity Method Investment, Ownership Percentage	56.00%
Ohio Gathering Company, LLC [Member]
Related Party Transaction [Line Items]
Equity Method Investment, Ownership Percentage	34.00%
Sherwood Midstream LLC [Member]
Related Party Transaction [Line Items]
Equity Method Investment, Ownership Percentage	50.00%
Sherwood Midstream Holdings [Member]
Related Party Transaction [Line Items]
Equity Method Investment, Ownership Percentage	86.00%
Transportation Services Agreements [Member] \| Transportation of crude and refined product services [Member] \| Commercial Agreements [Member] \| MPC
Related Party Transaction [Line Items]
Term Of Agreements	4 years
Number of Renewals	2
Three Year Storage Services Agreement [Member] \| Storage Services Tank Farm [Member] \| Commercial Agreements [Member] \| MPC
Related Party Transaction [Line Items]
Term Of Agreements	3 years
Ten Year Storage Services Agreement [Member] \| Storage Services Butane and Propane Caverns [Member] \| Commercial Agreements [Member] \| MPC
Related Party Transaction [Line Items]
Term Of Agreements	10 years
Terminal Services Agreements [Member] \| Terminal storage and related services [Member] \| Commercial Agreements [Member] \| MPC
Related Party Transaction [Line Items]
Term Of Agreements	5 years
Number of Renewals	2
Related Party Revolving Credit Agreement [Member] \| MPC Investment [Member]
Related Party Transaction [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 500
Line of Credit Facility, Expiration Date	Dec. 04, 2020
Debt Instrument, Description of Variable Rate Basis	LIBOR plus 1.50 percent
Proceeds from Long-term Lines of Credit	$ 0	$ 2,500
Repayments of Long-term Lines of Credit	0	2,500
Long-term debt, gross	$ 0	$ 0
Debt Instrument, Interest Rate, Effective Percentage	2.27%	1.939%

Number of Times for Automatic Renewal

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- Definition

Term Of Agreements

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- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

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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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- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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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.

+ References

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

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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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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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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