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RELATED PARTIES (Summary Of Other Ownership Interests) (Details) | Dec. 31, 2014 | Dec. 31, 2012
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Hibbing [Member] | Arcelor Mittal [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Ownership interest, equity method investment | 62.30%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = clf_ArcelorMittalMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = clf_HibbingMember |  |
Hibbing [Member] | WISCO [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Ownership interest, equity method investment | 0.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = clf_WiscoMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = clf_HibbingMember |  |
Hibbing [Member] | U. S. Steel Canada [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Ownership interest, equity method investment | 14.70%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = clf_USSteelCanadaMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = clf_HibbingMember |  |
Empire [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Noncontrolling Interest, Ownership Percentage by Parent | 79.00%us-gaap_MinorityInterestOwnershipPercentageByParent / clf_NameofOperationAxis = clf_EmpireMember |  |
Empire [Member] | Arcelor Mittal [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners | 21.00%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners / clf_NameofOperationAxis = clf_EmpireMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = clf_ArcelorMittalMember |  |
Empire [Member] | WISCO [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners | 0.00%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners / clf_NameofOperationAxis = clf_EmpireMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = clf_WiscoMember |  |
Empire [Member] | U. S. Steel Canada [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners | 0.00%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners / clf_NameofOperationAxis = clf_EmpireMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = clf_USSteelCanadaMember |  |
Tilden [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Noncontrolling Interest, Ownership Percentage by Parent | 85.00%us-gaap_MinorityInterestOwnershipPercentageByParent / clf_NameofOperationAxis = clf_TildenMember |  |
Tilden [Member] | Arcelor Mittal [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners | 0.00%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners / clf_NameofOperationAxis = clf_TildenMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = clf_ArcelorMittalMember |  |
Tilden [Member] | WISCO [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners | 0.00%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners / clf_NameofOperationAxis = clf_TildenMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = clf_WiscoMember |  |
Tilden [Member] | U. S. Steel Canada [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners | 15.00%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners / clf_NameofOperationAxis = clf_TildenMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = clf_USSteelCanadaMember |  |
Bloom Lake [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Noncontrolling Interest, Ownership Percentage by Parent | 82.80%us-gaap_MinorityInterestOwnershipPercentageByParent / clf_NameofOperationAxis = clf_BloomLakeMember |  | 75.00%us-gaap_MinorityInterestOwnershipPercentageByParent / clf_NameofOperationAxis = clf_BloomLakeMember
Bloom Lake [Member] | Arcelor Mittal [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners | 0.00%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners / clf_NameofOperationAxis = clf_BloomLakeMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = clf_ArcelorMittalMember |  |
Bloom Lake [Member] | WISCO [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners | 17.20%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners / clf_NameofOperationAxis = clf_BloomLakeMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = clf_WiscoMember |  |
Bloom Lake [Member] | U. S. Steel Canada [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners | 0.00%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners / clf_NameofOperationAxis = clf_BloomLakeMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = clf_USSteelCanadaMember |  |
Investments in Ventures [Member] | Hibbing [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Ownership interest, equity method investment | 23.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_BalanceSheetLocationAxis = clf_InvestmentsinVenturesMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = clf_HibbingMember | [1] |
[1] | 1 At December 31, 2013, the classification for Hibbing was Other liabilities.

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- Definition The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571 + Details
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