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STOCK COMPENSATION PLANS (Assumptions Utilized To Estimate Fair Value For Performance Share Grants) (Details) (Performance Shares [Member], USD $)
3 Months Ended
Mar. 31, 2015
January 12, 2015 [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Grant Date Market Price $ 7.70clf_ShareBasedCompensationArrangementByShareBasedPaymentAwardGrantDatePrice
/ us-gaap_AwardDateAxis
= clf_January122015Member
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Average Expected Term (Years) 2 years 11 months 20 days
Expected Volatility 58.30%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_AwardDateAxis
= clf_January122015Member
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Risk-Free Interest Rate 0.91%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_AwardDateAxis
= clf_January122015Member
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Dividend Yield 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_AwardDateAxis
= clf_January122015Member
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Fair Value $ 11.56us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardDateAxis
= clf_January122015Member
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Fair Value (Percent of Grant Date Market Price) 150.13%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPriceOfferingDate
/ us-gaap_AwardDateAxis
= clf_January122015Member
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
February 9, 2015 [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Grant Date Market Price $ 6.57clf_ShareBasedCompensationArrangementByShareBasedPaymentAwardGrantDatePrice
/ us-gaap_AwardDateAxis
= clf_February92015Member
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Average Expected Term (Years) 2 years 10 months 20 days
Expected Volatility 58.30%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_AwardDateAxis
= clf_February92015Member
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Risk-Free Interest Rate 0.87%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_AwardDateAxis
= clf_February92015Member
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Dividend Yield 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_AwardDateAxis
= clf_February92015Member
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Fair Value $ 9.86us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardDateAxis
= clf_February92015Member
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Fair Value (Percent of Grant Date Market Price) 150.13%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPriceOfferingDate
/ us-gaap_AwardDateAxis
= clf_February92015Member
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember