Commitments and Contingencies (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013
Commitments and Contingencies Disclosure [Abstract]
Commitments to acquire property, plant and equipment	$ 1,122

Commitments as of the balance sheet date to acquire property, plant and equipment.

No definition available.

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