SHAREHOLDERS' EQUITY Narrative (Details)	Mar. 31, 2013
Bloom Lake [Member]
Percentage Of Ownership Interests	75.00%
Tilden [Member]
Percentage Of Ownership Interests	85.00%
Empire [Member]
Percentage Of Ownership Interests	79.00%

The percentage of ownership of common stock or equity participation in the investee.

No definition available.

Name:	clf_PercentageOfOwnershipInterests
Namespace Prefix:	clf_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant