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STOCK COMPENSATION PLANS STOCK COMPENSATION PLANS (Nonemployee Directors) (Details) (Directors Plan [Member], USD $) | 3 Months Ended | 12 Months Ended
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Dec. 31, 2014 | Sep. 30, 2014 | Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Period from Date of Election, at End of Such Director is Required to Hold Certain Number of Shares |  |  | 5 years
Deferred Compensation Arrangement with Individual, Fair Value of Shares Issued |  |  | $ 250,000 us-gaap_DeferredCompensationArrangementWithIndividualFairValueOfSharesIssued
Stock Issued During Period Value Director Stock Award | $ 42,500 clf_StockIssuedDuringPeriodValueDirectorStockAward | $ 42,500 clf_StockIssuedDuringPeriodValueDirectorStockAward | $ 85,000 clf_StockIssuedDuringPeriodValueDirectorStockAward
Maximum [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized | 300,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_PlanNameAxis = clf_DirectorsPlanMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  | 300,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_PlanNameAxis = clf_DirectorsPlanMember / us-gaap_RangeAxis = us-gaap_MaximumMember

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- Definition Period from Date of Election, at End of Such Director is Required to Hold Certain Number of Shares + References No definition available. + Details
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- Definition Stock Issued During Period Value Director Stock Award + References No definition available. + Details
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- Definition The total fair value of shares issued during the period under a deferred compensation arrangement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Details
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- Definition The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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