Incentive Based Compensation Plans (Details 5-Performance) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2012
Performance Unit Disclosures [Abstract]
Performance Unit Granted	13
Performance Unit Awards Vesting Period	P36M

Performance units granted to executive officers upon achievement of certain goals. This is the number of units granted.

No definition available.

Name:	mro_AwardInstrumentsOtherThanOptionsPerformanceUnitGranted
Namespace Prefix:	mro_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration