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STOCK COMPENSATION PLANS STOCK COMPENSATION PLANS (Incentive Compensation and Other Benefit Plans for Employees and Directors) (Details) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Restricted Equity Grant Shares [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Stock Issued During Period Shares Director Stock Award | 73,635 clf_StockIssuedDuringPeriodSharesDirectorStockAward / us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis = clf_RestrictedEquityGrantSharesMember | 31,506 clf_StockIssuedDuringPeriodSharesDirectorStockAward / us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis = clf_RestrictedEquityGrantSharesMember | 8,988 clf_StockIssuedDuringPeriodSharesDirectorStockAward / us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis = clf_RestrictedEquityGrantSharesMember
Deferred Equity Grant Shares [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Stock Issued During Period Shares Director Stock Award | 0 clf_StockIssuedDuringPeriodSharesDirectorStockAward / us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis = clf_DeferredEquityGrantSharesMember | 7,970 clf_StockIssuedDuringPeriodSharesDirectorStockAward / us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis = clf_DeferredEquityGrantSharesMember | 2,996 clf_StockIssuedDuringPeriodSharesDirectorStockAward / us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis = clf_DeferredEquityGrantSharesMember
Unrestricted Equity Grant Shares [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Stock Issued During Period Shares Director Stock Award | 0 clf_StockIssuedDuringPeriodSharesDirectorStockAward / us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis = clf_UnrestrictedEquityGrantSharesMember | 3,985 clf_StockIssuedDuringPeriodSharesDirectorStockAward / us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis = clf_UnrestrictedEquityGrantSharesMember | 1,498 clf_StockIssuedDuringPeriodSharesDirectorStockAward / us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis = clf_UnrestrictedEquityGrantSharesMember

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