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Commercial Agreements [Abstract]

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Loan Agreement [Abstract]

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Number of Times for Automatic Renewal

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- Definition

Renewal Term Agreement

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Term Of Agreements

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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.

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

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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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.

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

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The effective interest rate during the reporting period.

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Amount of asset related to consideration paid in advance for insurance that provides economic benefits within a future period of one year or the normal operating cycle, if longer.

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Amount of cash inflow from contractual arrangement with the lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

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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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Purchases during the period (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

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Amount of cash outflow for payment of an obligation from a lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

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Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

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Related Party Agreements and Transactions (Narrative) (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Apr. 26, 2018 USD ($)
Loan Agreement [Abstract]
Revenue from related parties	$ 5	$ 11
Purchases from related parties	8	44
MPC
Loan Agreement [Abstract]
Prepaid insurance	1	8
Purchases from related parties	168	3	$ 0
MPC Investment \| Related Party Revolving Credit Agreement
Loan Agreement [Abstract]
Current borrowing capacity	$ 1,000			$ 500
Expiration date	Dec. 04, 2020
Description of variable rate basis	LIBOR plus 1.50 percent
Proceeds from lines of credit	$ 4,000	2,400
Repayments of lines of credit	4,300	2,000
Outstanding balance	$ 0	$ 386
Interest rate during period	3.473%	2.777%
Commercial Agreements \| MPC \| Transportation Services Agreements [Member] \| Minimum \| Crude oil and product pipeline
Commercial Agreements
Term Of Agreements	5 years
Automatic renewal term agreement	2 years
Commercial Agreements \| MPC \| Transportation Services Agreements [Member] \| Maximum \| Crude oil and product pipeline
Commercial Agreements
Term Of Agreements	15 years
Automatic renewal term agreement	5 years
Commercial Agreements \| MPC \| Five Year Transportation Services Agreement [Member] \| Handling crude oil and products
Commercial Agreements
Term Of Agreements	5 years
Commercial Agreements \| MPC \| Six Year Transportation Services Agreement [Member] \| Providing marine transportation of crude oil, feedstocks and refined petroleum products, and related services
Commercial Agreements
Term Of Agreements	6 years
Commercial Agreements \| MPC \| Ten Year Storage Services Agreement [Member] \| Storage services tank farms
Commercial Agreements
Term Of Agreements	10 years
Commercial Agreements \| MPC \| Seventeen Year Storage Services Agreement [Member] \| Storage services tank farms
Commercial Agreements
Term Of Agreements	17 years
Commercial Agreements \| MPC \| Three Year Storage Services Agreement [Member] \| Storage services tank farms
Commercial Agreements
Renewal term agreement	5 years
Term Of Agreements	3 years
Commercial Agreements \| MPC \| Three Year Storage Services Agreement [Member] \| Crude oil and product pipeline
Commercial Agreements
Term Of Agreements	3 years
Commercial Agreements \| MPC \| Storage Services Agreements \| Storage services tank farms
Commercial Agreements
Renewal term agreement	5 years
Automatic renewal term agreement	1 year
Commercial Agreements \| MPC \| Storage Services Agreements \| Minimum \| Storage services tank farms
Commercial Agreements
Automatic renewal term agreement	0 years
Commercial Agreements \| MPC \| Storage Services Agreements \| Maximum \| Storage services tank farms
Commercial Agreements
Automatic renewal term agreement	10 years
Commercial Agreements \| MPC \| Ten Year Terminal Services Agreement [Member] \| Refined products
Commercial Agreements
Term Of Agreements	10 years
Commercial Agreements \| MPC \| Terminal Services Agreements \| Minimum \| Refined products
Commercial Agreements
Automatic renewal term agreement	2 years
Commercial Agreements \| MPC \| Terminal Services Agreements \| Maximum \| Refined products
Commercial Agreements
Automatic renewal term agreement	5 years
Commercial Agreements \| MPC \| Management Services Agreements [Member] \| Co-location Agreements [Member]
Commercial Agreements
Term Of Agreements	50 years
Commercial Agreements \| MPC \| Management Services Agreements [Member] \| Marine Management Services [Member]
Commercial Agreements
Automatic renewal term agreement	5 years
Number of renewals	2
Commercial Agreements \| MPC \| Lease Agreements [Member] \| Management Services Agreements [Member]
Commercial Agreements
Term Of Agreements	50 years
Operating Agreements \| MPC \| Minimum
Commercial Agreements
Term Of Agreements	1 year
Operating Agreements \| MPC \| Maximum
Commercial Agreements
Term Of Agreements	5 years
MarkWest Utica EMG
Related Party Transaction [Line Items]
Equity method investment, ownership percentage	56.00%
Ohio Gathering
Related Party Transaction [Line Items]
Equity method investment, ownership percentage	34.00%
Sherwood Midstream LLC
Related Party Transaction [Line Items]
Equity method investment, ownership percentage	50.00%
Sherwood Midstream Holdings
Related Party Transaction [Line Items]
Equity method investment, ownership percentage	80.00%
Jefferson Dry Gas
Related Party Transaction [Line Items]
Equity method investment, ownership percentage	67.00%