Annual report pursuant to Section 13 and 15(d)

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) Details of Accumulated Other Comprehensive Income (Loss) Components (Details)

v2.4.1.9
ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) Details of Accumulated Other Comprehensive Income (Loss) Components (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Details of Accumulated Other Comprehensive Income (Loss) Components [Line Items]      
Derivative Instruments, (Gain) Loss Reclassified from Accumulated OCI into Income, Effective Portion, Net $ (31.0)us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet $ (22.1)us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet $ 18.1us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
Total Amount Reclassified from Accumulated Other Comprehensive Income (Loss) During the Period 33.3clf_TotalAmountReclassifiedFromAccumulatedOtherComprehensiveIncomeLossDuringPeriod 53.6clf_TotalAmountReclassifiedFromAccumulatedOtherComprehensiveIncomeLossDuringPeriod  
Accumulated Defined Benefit Plans Adjustment [Member]      
Details of Accumulated Other Comprehensive Income (Loss) Components [Line Items]      
Amortization of prior service (cost) credit 0.9us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
[1] 0.6us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
[1]  
Defined Benefit Plan, Amortization of Gains (Losses) 19.1us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
[1] 41.4us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
[1]  
Defined Benefit Plan, Curtailments (5.0)us-gaap_DefinedBenefitPlanCurtailments
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
0us-gaap_DefinedBenefitPlanCurtailments
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= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
 
Defined Benefit Plan, Special Termination Benefits 3.4us-gaap_DefinedBenefitPlanSpecialTerminationBenefits
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
0us-gaap_DefinedBenefitPlanSpecialTerminationBenefits
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= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
 
Other Comprehensive Income (Loss), Reclassification, Pension and Other Postretirement Benefit Plans, Net Gain (Loss) Recognized in Net Periodic Benefit Cost, before Tax 16.6us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
40.8us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
 
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, Tax (5.8)us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
(14.3)us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
 
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) 10.8us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
26.5us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
 
Unrealized Gain (Loss) on Marketable Securities [Member] [Member]      
Details of Accumulated Other Comprehensive Income (Loss) Components [Line Items]      
Marketable Securities, Unrealized Gain (Loss) (11.4)us-gaap_MarketableSecuritiesUnrealizedGainLoss
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_UnrealizedGainLossonMarketableSecuritiesMemberMember
(0.2)us-gaap_MarketableSecuritiesUnrealizedGainLoss
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_UnrealizedGainLossonMarketableSecuritiesMemberMember
 
Accumulated Other-than-Temporary Impairment [Member]      
Details of Accumulated Other Comprehensive Income (Loss) Components [Line Items]      
Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Loss, before Tax, Including Portion Attributable to Noncontrolling Interest, Available-for-sale Securities (0.5)us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionInOtherComprehensiveIncomeLossBeforeTaxIncludingPortionAttributableToNoncontrollingInterestAvailableforsaleSecurities
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedOtherThanTemporaryImpairmentMember
5.3us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionInOtherComprehensiveIncomeLossBeforeTaxIncludingPortionAttributableToNoncontrollingInterestAvailableforsaleSecurities
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedOtherThanTemporaryImpairmentMember
 
Unrealized Gain (Loss) on Marketable Securities and Other than Temporary Impairment [Member] [Member]      
Details of Accumulated Other Comprehensive Income (Loss) Components [Line Items]      
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, before Tax (11.9)us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_UnrealizedGainLossonMarketableSecuritiesandOtherthanTemporaryImpairmentMember
5.1us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_UnrealizedGainLossonMarketableSecuritiesandOtherthanTemporaryImpairmentMember
 
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax 3.4us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_UnrealizedGainLossonMarketableSecuritiesandOtherthanTemporaryImpairmentMember
(0.1)us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_UnrealizedGainLossonMarketableSecuritiesandOtherthanTemporaryImpairmentMember
 
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax (8.5)us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_UnrealizedGainLossonMarketableSecuritiesandOtherthanTemporaryImpairmentMember
5.0us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_UnrealizedGainLossonMarketableSecuritiesandOtherthanTemporaryImpairmentMember
 
Unrealized Gain Loss On Derivatives [Member]      
Details of Accumulated Other Comprehensive Income (Loss) Components [Line Items]      
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax 45.6us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodBeforeTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_UnrealizedGainLossOnDerivativesMember
32.3us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodBeforeTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_UnrealizedGainLossOnDerivativesMember
 
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax (14.6)us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_UnrealizedGainLossOnDerivativesMember
(10.2)us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_UnrealizedGainLossOnDerivativesMember
 
Unrealized net gain (loss) on derivative financial instruments, net of tax 31.0us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodNetOfTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_UnrealizedGainLossOnDerivativesMember
22.1us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodNetOfTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_UnrealizedGainLossOnDerivativesMember
 
Unrealized Gain Loss On Derivatives [Member] | Australian Hedge Contracts [Member]      
Details of Accumulated Other Comprehensive Income (Loss) Components [Line Items]      
Derivative Instruments, (Gain) Loss Reclassified from Accumulated OCI into Income, Effective Portion, Net 18.9us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_AustralianHedgeContractsMember
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_UnrealizedGainLossOnDerivativesMember
17.0us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_AustralianHedgeContractsMember
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_UnrealizedGainLossOnDerivativesMember
 
Unrealized Gain Loss On Derivatives [Member] | Canadian Hedge Contracts [Member]      
Details of Accumulated Other Comprehensive Income (Loss) Components [Line Items]      
Derivative Instruments, (Gain) Loss Reclassified from Accumulated OCI into Income, Effective Portion, Net $ 26.7us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianHedgeContractsMember
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_UnrealizedGainLossOnDerivativesMember
$ 15.3us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianHedgeContractsMember
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_UnrealizedGainLossOnDerivativesMember
 
[1] hese accumulated other comprehensive income components are included in the net periodic benefit cost recognized for the year ended December 31, 2014 and 2013. See NOTE 7 - PENSIONS AND OTHER POSTRETIREMENT BENEFITS for further information.