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Acquisitions and Investments (Investments in Ethanol Companies) (Details) (USD $)
In Millions, unless otherwise specified
1 Months Ended
Aug. 01, 2013
Company
Dec. 31, 2014
TACE    
Business Acquisition [Line Items]    
Equity method investments, ownership percentage   60.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= mpc_AndersonsClymersEthanolLlcMember
TAEI    
Business Acquisition [Line Items]    
Equity method investments, ownership percentage   34.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= mpc_AndersonsEthanolInvestmentLlcMember
TAME    
Business Acquisition [Line Items]    
Equity method investments, ownership percentage   67.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= mpc_AndersonsMarathonEthanolLlcMember
TAME | TAEI    
Business Acquisition [Line Items]    
Equity method investments, ownership percentage   50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ dei_LegalEntityAxis
= mpc_TheAndersonsEthanolInvestmentLlcMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= mpc_AndersonsMarathonEthanolLlcMember
TAAE    
Business Acquisition [Line Items]    
Equity method investments, ownership percentage   43.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= mpc_AndersonsAlbionEthanolLlcMember
Ethanol Interests From Mitsui    
Business Acquisition [Line Items]    
Number of businesses in which ownership interests acquired 3mpc_NumberOfBusinessesInWhichOwnershipInterestsAcquired
/ us-gaap_BusinessAcquisitionAxis
= mpc_EthanolInterestsFromMitsuiMember
 
Cash paid to acquire equity method investments $ 75us-gaap_PaymentsToAcquireEquityMethodInvestments
/ us-gaap_BusinessAcquisitionAxis
= mpc_EthanolInterestsFromMitsuiMember
 
Ethanol Interests From Mitsui | TACE    
Business Acquisition [Line Items]    
Ownership percentage acquired 24.00%us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired
/ us-gaap_BusinessAcquisitionAxis
= mpc_EthanolInterestsFromMitsuiMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= mpc_AndersonsClymersEthanolLlcMember
 
Ethanol Interests From Mitsui | TAEI    
Business Acquisition [Line Items]    
Ownership percentage acquired 34.00%us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired
/ us-gaap_BusinessAcquisitionAxis
= mpc_EthanolInterestsFromMitsuiMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= mpc_AndersonsEthanolInvestmentLlcMember
 
Ethanol Interests From Mitsui | TAAE    
Business Acquisition [Line Items]    
Ownership percentage acquired 40.00%us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired
/ us-gaap_BusinessAcquisitionAxis
= mpc_EthanolInterestsFromMitsuiMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= mpc_AndersonsAlbionEthanolLlcMember