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Fair Value Measurements - Recurring Narrative (Detail)	9 Months Ended
	Sep. 30, 2019 USD ($)
Embedded derivatives in commodity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Embedded derivative renewal term	5 years
Level 3 | Commodity derivatives | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Forward commodity price	$ 0.41
Level 3 | Commodity derivatives | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Forward commodity price	$ 1.07
Level 3 | Embedded derivatives in commodity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Probability of renewal first term	93.00%
Probability of renewal second term	82.50%

X

- 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

X

- Definition

Represents the forward commodity price used as an input to measure fair value.

+ References

No definition available.

+ Details

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Namespace Prefix:	mpc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Represents the percentage of likelihood of renewal of the commodity contract with embedded derivative.

+ References

No definition available.

+ Details

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Namespace Prefix:	mpc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- 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

X

- 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

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X

- Details

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X

- Details

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X

- Details

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- Details

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- Details

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