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Fair Value Measurements - Recurring (Significant Unobservable Inputs in Level 3 Valuation) (Details) - Significant unobservable inputs (Level 3) | 12 Months Ended
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Dec. 31, 2018 USD ($)
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |
Term of counterparty option to renew gas purchase agreement | 5 years
Commodity contracts | Minimum |
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |
Fair value inputs commodity price | $ 0.58
Commodity contracts | Maximum |
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |
Fair value inputs commodity price | $ 1.01
Embedded derivatives in commodity contracts |
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items] |
Probability of renewal, first term | 90.00%
Probability of renewal, second term | 80.00%

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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
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Namespace Prefix: | mpc_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition [Line Items] for Schedule of the inputs used in the fair value measurement of assets and liabilities. This disclosure may include, but is not limited to, the fair value of the asset and liabilities, valuation technique used to measure fair value, the inputs used to measure fair value, the ranges of the inputs, and the weighted averages of the inputs. [Table] + References No definition available. + Details
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Namespace Prefix: | mpc_
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Balance Type: | na
Period Type: | duration

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- Definition Represents the forward commodity price used as an input to measure fair value. + References No definition available. + Details
Name: | mpc_FairValueInputsForwardCommodityPrice
Namespace Prefix: | mpc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Represents the percentage of likelihood of renewal of the commodity contract with embedded derivative. + References No definition available. + Details
Name: | mpc_FairValueInputsProbabilityOfRenewal
Namespace Prefix: | mpc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Represents the percentage of likelihood of renewal of the commodity contract with embedded derivative for the second term of the contract. + References No definition available. + Details
Name: | mpc_FairValueInputsProbabilityofRenewalSecondTerm
Namespace Prefix: | mpc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Details
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- Details
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- Details
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- Details
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- Details
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