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Quarterly report pursuant to Section 13 or 15(d)

STOCK COMPENSATION PLANS (Assumptions Utilized To Estimate Fair Value For Performance Share Grants) (Details)

v2.4.1.9
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] Ìý
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Ìý
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] Ìý
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Ìý
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