| SHAREHOLDERS' EQUITY Narrative (Details) | Mar. 31, 2015 | 
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| Empire [Member] | |
| Noncontrolling Interest, Ownership Percentage by Parent | 79.00%us-gaap_MinorityInterestOwnershipPercentageByParent / clf_NameofOperationAxis = clf_EmpireMember | 
| Tilden [Member] | |
| Noncontrolling Interest, Ownership Percentage by Parent | 85.00%us-gaap_MinorityInterestOwnershipPercentageByParent / clf_NameofOperationAxis = clf_TildenMember | 
| Bloom Lake [Member] | |
| Noncontrolling Interest, Ownership Percentage by Parent | 82.80%us-gaap_MinorityInterestOwnershipPercentageByParent / clf_NameofOperationAxis = clf_BloomLakeMember | 
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- Definition The parent entity's interest in net assets of the subsidiary, expressed as a percentage. No definition available. 
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