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Derivative Financial Instruments (Embedded Derivatives in Commodity Contracts) (Details) - Embedded derivative in natural gas processing and purchase contract [Member] - Embedded derivatives in commodity contracts $ in Millions | 12 Months Ended |
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Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($)
Derivative [Line Items] |  |
Number of renewals | 2 |
Term of counterparty option to renew gas purchase agreement | 5 years |
Embedded derivative fair value of embedded derivative liability including inception value allocable to host contract | $ 61 | $ 64

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- Definition Fair value as of the balance sheet date of a natural gas purchase agreement embedded in a gas processing agreement. The natural gas purchase agreement is an embedded derivative. This amount includes the value of the embedded purchase agreement at the inception of the arrangement. however, in accordance with GAAP, the fair value of the embedded derivative at inception is deemed to be allocable to the host contract and is not separately recorded as an embedded derivative. + References No definition available. + Details
Name: | mpc_EmbeddedDerivativeFairValueOfEmbeddedDerivativeLiabilityIncludingInceptionValueAllocableToHostContract
Namespace Prefix: | mpc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Represents the term for which the counterparty has the option to renew a purchase agreement related to an embedded derivative. + References No definition available. + Details
Name: | mpc_EmbeddedDerivativeRenewalTerm
Namespace Prefix: | mpc_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition Number of Times for Automatic Renewal + References No definition available. + Details
Name: | mpc_NumberofRenewals
Namespace Prefix: | mpc_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | instant

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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_DerivativeLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | mpc_CommodityTypeAxis=mpc_NaturalGasMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=us-gaap_EmbeddedDerivativeFinancialInstrumentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |