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Derivative Financial Instruments - Embedded Derivatives in Commodity Contracts (Details) $ in Millions		3 Months Ended
		Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Natural Gas [Member] | Embedded derivatives in commodity contracts
Derivative [Line Items]
Number of Renewals		2
Embedded Derivative Renewal Term		5 years
Embedded Derivative Fair Value of Embedded Derivative Liability Including Inception Value Allocable to Host Contract		$ 59	$ 64
Not Designated as Hedging Instrument [Member] | Commodity contracts
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	[1]	60	66
Not Designated as Hedging Instrument [Member] | Other Noncurrent Liabilities [Member] | Commodity contracts
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	[1]	$ 48	$ 52
[1] Includes embedded derivatives in commodity contracts as discussed above.

X

- 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

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

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

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

X

- 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

X

- Definition

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=82924980&loc=SL51823488-111719

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624163-113959

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82849420&loc=SL20226000-175313

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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

X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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

X

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_NondesignatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_CommodityContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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Namespace Prefix:
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Period Type: