Annual report pursuant to Section 13 and 15(d)

STOCK COMPENSATION PLANS STOCK COMPENSATION PLANS (Incentive Compensation and Other Benefit Plans for Employees and Directors) (Details)

v2.4.1.9
STOCK COMPENSATION PLANS STOCK COMPENSATION PLANS (Incentive Compensation and Other Benefit Plans for Employees and Directors) (Details)
12 Months Ended
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 73,635clf_StockIssuedDuringPeriodSharesDirectorStockAward
/ us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis
= clf_RestrictedEquityGrantSharesMember
31,506clf_StockIssuedDuringPeriodSharesDirectorStockAward
/ us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis
= clf_RestrictedEquityGrantSharesMember
8,988clf_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 0clf_StockIssuedDuringPeriodSharesDirectorStockAward
/ us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis
= clf_DeferredEquityGrantSharesMember
7,970clf_StockIssuedDuringPeriodSharesDirectorStockAward
/ us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis
= clf_DeferredEquityGrantSharesMember
2,996clf_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 0clf_StockIssuedDuringPeriodSharesDirectorStockAward
/ us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis
= clf_UnrestrictedEquityGrantSharesMember
3,985clf_StockIssuedDuringPeriodSharesDirectorStockAward
/ us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis
= clf_UnrestrictedEquityGrantSharesMember
1,498clf_StockIssuedDuringPeriodSharesDirectorStockAward
/ us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis
= clf_UnrestrictedEquityGrantSharesMember