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Supplemental Cash Flow Information (Summary of Reconciliation of Additions to Property, Plant and Equipment to Total Capital Expenditures) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental Cash Flow Elements [Abstract]
Increase/(decrease) in capital accruals	$ 104	$ 71	$ (22)

X

- Definition

Increase (Decrease) In Capital Accruals

+ References

No definition available.

+ Details

Name:	mpc_IncreaseDecreaseInCapitalAccruals
Namespace Prefix:	mpc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- References

No definition available.

+ Details

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