COMMITMENTS AND CONTINGENCIES - Narrative (Details)	Sep. 26, 2012 area
Commitments and Contingencies Disclosure [Abstract]
Number of manufacturing plant areas to be investigated	4
Duration of plant operations	60 years

Number Of Manufacturing Plant Areas To Be Investigated

No definition available.

Name:	clf_NumberOfManufacturingPlantAreasToBeInvestigated
Namespace Prefix:	clf_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant