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Related Party Agreements and Transactions (Purchases - Related Party) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Related Party Transaction [Line Items] |  |  |
Purchases from related parties | $ 8 | $ 44 |
MPC |  |  |
Related Party Transaction [Line Items] |  |  |
Purchases from related parties | $ 168 | $ 3 | $ 0

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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. + References No definition available. + Details
Name: | us-gaap_RelatedPartyTransactionLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Purchases during the period (excluding transactions that are eliminated in consolidated or combined financial statements) with related party. + References No definition available. + Details
Name: | us-gaap_RelatedPartyTransactionPurchasesFromRelatedParty
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
Name: | us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=mpc_MarathonPetroleumCorporationMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |