Derivative Financial Instruments (Embedded Derivatives in Commodity Contracts) (Details) $ in Millions	12 Months Ended
Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Derivative [Line Items]
Term of counterparty option to renew gas purchase agreement	5 years
Embedded derivative in natural gas processing and purchase contract [Member] \| Embedded derivatives in commodity contracts
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	$ 60	$ 61

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.

No definition available.

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