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Dispositions (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended 1 Months Ended 3 Months Ended 1 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Jun. 30, 2014
Jun. 30, 2013
Feb. 28, 2013
Jan. 31, 2013
Sep. 30, 2012
Jan. 31, 2012
May 31, 2012
Dispositions Detail [Line Items]                    
Proceeds from Sale of Oil and Gas Property and Equipment $ 3,760us-gaap_ProceedsFromSaleOfOilAndGasPropertyAndEquipment $ 450us-gaap_ProceedsFromSaleOfOilAndGasPropertyAndEquipment $ 467us-gaap_ProceedsFromSaleOfOilAndGasPropertyAndEquipment              
Williston Basin [Member]                    
Dispositions Detail [Line Items]                    
Proceeds from Sale of Oil and Gas Property and Equipment       90us-gaap_ProceedsFromSaleOfOilAndGasPropertyAndEquipment
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= mro_WillistonBasinMember
           
Pretax gain/loss on sale       91us-gaap_SignificantAcquisitionsAndDisposalsGainLossOnSaleOrDisposalPretax
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= mro_WillistonBasinMember
           
DJ Basin [Member]                    
Dispositions Detail [Line Items]                    
Proceeds from Sale of Oil and Gas Property and Equipment         19us-gaap_ProceedsFromSaleOfOilAndGasPropertyAndEquipment
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= mro_DjBasinMember
         
Pretax gain/loss on sale         114us-gaap_SignificantAcquisitionsAndDisposalsGainLossOnSaleOrDisposalPretax
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= mro_DjBasinMember
         
Marcellus Shale [Member]                    
Dispositions Detail [Line Items]                    
Pretax gain/loss on sale           43us-gaap_SignificantAcquisitionsAndDisposalsGainLossOnSaleOrDisposalPretax
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= mro_MarcellusShaleMember
       
Neptune Gas Plant [Member]                    
Dispositions Detail [Line Items]                    
Proceeds from Sale of Oil and Gas Property and Equipment           166us-gaap_ProceedsFromSaleOfOilAndGasPropertyAndEquipment
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= mro_NeptuneGasPlantMember
       
Pretax gain/loss on sale           (98)us-gaap_SignificantAcquisitionsAndDisposalsGainLossOnSaleOrDisposalPretax
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= mro_NeptuneGasPlantMember
       
Alaska EP [Member]                    
Dispositions Detail [Line Items]                    
Proceeds from Sale of Oil and Gas Property and Equipment             195us-gaap_ProceedsFromSaleOfOilAndGasPropertyAndEquipment
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= mro_AlaskaEpMember
     
Proceeds from Sale of Oil and Gas Property and Equipment, Six Month Escrow             50mro_ProceedsFromSaleOfOilAndGasPropertyAndEquipmentSixMonthEscrow
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= mro_AlaskaEpMember
     
Pretax gain/loss on sale         (55)us-gaap_SignificantAcquisitionsAndDisposalsGainLossOnSaleOrDisposalPretax
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= mro_AlaskaEpMember
         
Safen Block [Member]                    
Dispositions Detail [Line Items]                    
Pretax gain/loss on sale   17us-gaap_SignificantAcquisitionsAndDisposalsGainLossOnSaleOrDisposalPretax
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= mro_SafenBlockMemberMember
               
Interest Percentage   45.00%mro_InterestPercentage
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= mro_SafenBlockMemberMember
               
Eagle Ford Shale Member [Member]                    
Dispositions Detail [Line Items]                    
Proceeds from Sale of Oil and Gas Property and Equipment               9us-gaap_ProceedsFromSaleOfOilAndGasPropertyAndEquipment
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= mro_EagleFordShaleMemberMember
   
Pretax gain/loss on sale               18us-gaap_SignificantAcquisitionsAndDisposalsGainLossOnSaleOrDisposalPretax
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= mro_EagleFordShaleMemberMember
   
GOM Pipelines [Member]                    
Dispositions Detail [Line Items]                    
Proceeds from Sale of Oil and Gas Property and Equipment                 206us-gaap_ProceedsFromSaleOfOilAndGasPropertyAndEquipment
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= mro_GomPipelinesMember
 
Pretax gain/loss on sale                 (166)us-gaap_SignificantAcquisitionsAndDisposalsGainLossOnSaleOrDisposalPretax
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= mro_GomPipelinesMember
 
INDONESIA                    
Dispositions Detail [Line Items]                    
Pretax gain/loss on sale                   $ 36us-gaap_SignificantAcquisitionsAndDisposalsGainLossOnSaleOrDisposalPretax
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= country_ID