Property, Plant and Equipment (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property, Plant and Equipment [Abstract]
Amounts capitalized less than one year after completion of drilling	$ 484	$ 512	$ 388
Amounts capitalized greater than one year after completion of drilling	126	281	229
Total deferred exploratory well costs	610us-gaap_CapitalizedExploratoryWellCosts	793us-gaap_CapitalizedExploratoryWellCosts	617us-gaap_CapitalizedExploratoryWellCosts
Projects that have Exploratory Well Costs that have been Capitalized for Period Greater than One Year, Number of Projects	3	7	6
Increase (Decrease) in Capitalized Exploratory Well Costs that are Pending Determination of Proved Reserves [Roll Forward]
Beginning balance	793us-gaap_CapitalizedExploratoryWellCosts	617us-gaap_CapitalizedExploratoryWellCosts	704us-gaap_CapitalizedExploratoryWellCosts
Additions	808	746	699
Dry well expense	(206)	(147)	(111)
Transfers to development	(605)	(414)	(629)
Dispositions	(180)	(9)	(46)
Ending balance	$ 610us-gaap_CapitalizedExploratoryWellCosts	$ 793us-gaap_CapitalizedExploratoryWellCosts	$ 617us-gaap_CapitalizedExploratoryWellCosts

Previously capitalized costs of the drilling of wells that were sold in the period

No definition available.

Name:	mro_CapitalizedExploratoryWellCostPeriodIncreaseDecreaseForSoldAssets
Namespace Prefix:	mro_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Additions to capitalized exploratory well costs that were added during the reporting period pending the determination of proved reserves.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 1B

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=8451039&loc=SL6806780-109447

+ Details

Name:	us-gaap_CapitalizedExploratoryWellCostAdditionsPendingDeterminationOfProvedReserves
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Capitalized exploratory well costs that were expensed during the year because proved reserves were not found at the exploratory well.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 1B

-Subparagraph (a)(3)

-URI http://asc.fasb.org/extlink&oid=8451039&loc=SL6806780-109447

+ Details

Name:	us-gaap_CapitalizedExploratoryWellCostChargedToExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amount of capitalized exploratory well costs that is pending the determination of proved reserves. This does not include amounts that were capitalized and subsequently expensed in the same annual period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 1B

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=8451039&loc=SL6806780-109447

+ Details

Name:	us-gaap_CapitalizedExploratoryWellCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of exploratory well costs that have been capitalized for a period of greater than one year after the completion of drilling.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 1B

-Subparagraph b

-URI http://asc.fasb.org/extlink&oid=8451039&loc=SL6806780-109447

+ Details

Name:	us-gaap_CapitalizedExploratoryWellCostsThatHaveBeenCapitalizedForPeriodGreaterThanOneYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of exploratory well costs that have been capitalized for a period of one year or less after the completion of drilling.

+ References

No definition available.

+ Details

Name:	us-gaap_CapitalizedExploratoryWellCostsThatHaveBeenCapitalizedForPeriodOfOneYearOrLess
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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

- Definition

The number of projects for which exploratory well costs have been capitalized for a period of greater than one year after the completion of drilling.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 1B

-Subparagraph b

-URI http://asc.fasb.org/extlink&oid=8451039&loc=SL6806780-109447

+ Details

Name:	us-gaap_ProjectsThatHaveExploratoryWellCostsThatHaveBeenCapitalizedForPeriodGreaterThanOneYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Details

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

- Definition

Previously capitalized costs of the drilling of wells that were reclassified as part of the costs of the enterprise's wells and related equipment and facilities at the time that proved reserves were found.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 1B

-Subparagraph (a)(2)

-URI http://asc.fasb.org/extlink&oid=8451039&loc=SL6806780-109447

+ Details

Name:	us-gaap_ReclassificationToWellFacilitiesAndEquipmentBasedOnDeterminationOfProvedReserves
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration