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Quarterly report pursuant to Section 13 or 15(d)

STOCK COMPENSATION PLANS Stock Option Activity (Details)

v2.4.1.9
STOCK COMPENSATION PLANS Stock Option Activity (Details) (Employee Stock Option [Member], January 12, 2015 [Member], USD $)
3 Months Ended
Mar. 31, 2015
Employee Stock Option [Member] | January 12, 2015 [Member]
Ìý
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] Ìý
Share Based Compensation Arrangement By Share Based Payment Award Grant Date Price $ 7.70clf_ShareBasedCompensationArrangementByShareBasedPaymentAwardGrantDatePrice
/ us-gaap_AwardDateAxis
= clf_January122015Member
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term 6 years 5 months 20 days
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate 75.30%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_AwardDateAxis
= clf_January122015Member
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate 1.60%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_AwardDateAxis
= clf_January122015Member
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_AwardDateAxis
= clf_January122015Member
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value $ 5.23us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardDateAxis
= clf_January122015Member
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember