Quarterly report pursuant to Section 13 or 15(d)

SHAREHOLDERS' EQUITY Details of Accumulated Other Comprehensive Income (Loss) Components (Details)

v2.4.1.9
SHAREHOLDERS' EQUITY Details of Accumulated Other Comprehensive Income (Loss) Components (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]    
Derivative Instruments, (Gain) Loss Reclassified from Accumulated OCI into Income, Effective Portion, Net $ (6.3)us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet $ (12.8)us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax 195.5us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax 16.1us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax
Accumulated Defined Benefit Plans Adjustment [Member]    
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]    
Defined Benefit Plan, Amortization of Prior Service Cost (Credit) (0.3)us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
[1] (0.3)us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
[1]
Defined Benefit Plan, Amortization of Gains (Losses) 8.5us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
[1] 4.8us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
[1]
Defined Benefit Plan, Curtailments 0.3us-gaap_DefinedBenefitPlanCurtailments
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
[1] 0.3us-gaap_DefinedBenefitPlanCurtailments
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
[1]
Other Comprehensive Income (Loss), Reclassification, Pension and Other Postretirement Benefit Plans, Net Gain (Loss) Recognized in Net Periodic Benefit Cost, before Tax 8.5us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
4.8us-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 0us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
(1.6)us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) 8.5us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
3.2us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
Realized Gain (Loss) on Marketable Securities [Member]    
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]    
Marketable Securities, Realized Gain (Loss) 0us-gaap_MarketableSecuritiesRealizedGainLoss
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_RealizedGainLossonMarketableSecuritiesMember
0.1us-gaap_MarketableSecuritiesRealizedGainLoss
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_RealizedGainLossonMarketableSecuritiesMember
Accumulated Other-than-Temporary Impairment [Member]    
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [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 (2.0)us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionInOtherComprehensiveIncomeLossBeforeTaxIncludingPortionAttributableToNoncontrollingInterestAvailableforsaleSecurities
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedOtherThanTemporaryImpairmentMember
0us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionInOtherComprehensiveIncomeLossBeforeTaxIncludingPortionAttributableToNoncontrollingInterestAvailableforsaleSecurities
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= us-gaap_AccumulatedOtherThanTemporaryImpairmentMember
Realized Gain (Loss) on Marketable Securities and Other than Temporary Impairment [Member]    
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]    
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities and Impairment on Securities Arising During Period, before tax (2.0)clf_OtherComprehensiveIncomeLossRealizedHoldingGainLossonSecuritiesandImpairmentonSecuritiesArisingDuringPeriodbeforetax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_RealizedGainLossonMarketableSecuritiesandOtherthanTemporaryImpairmentMember
0.1clf_OtherComprehensiveIncomeLossRealizedHoldingGainLossonSecuritiesandImpairmentonSecuritiesArisingDuringPeriodbeforetax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_RealizedGainLossonMarketableSecuritiesandOtherthanTemporaryImpairmentMember
Other Comprehensive Income (Loss), Realized Holding Gain (Loss) on Securities and Impairment on Securities Arising During Period, Tax 0clf_OtherComprehensiveIncomeLossRealizedHoldingGainLossonSecuritiesandImpairmentonSecuritiesArisingDuringPeriodTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_RealizedGainLossonMarketableSecuritiesandOtherthanTemporaryImpairmentMember
0clf_OtherComprehensiveIncomeLossRealizedHoldingGainLossonSecuritiesandImpairmentonSecuritiesArisingDuringPeriodTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_RealizedGainLossonMarketableSecuritiesandOtherthanTemporaryImpairmentMember
Other Comprehensive Income (Loss), Realized Holding Gain (Loss) on Securities and Impairment on Securities Arising During Period, net of tax (2.0)clf_OtherComprehensiveIncomeLossRealizedHoldingGainLossonSecuritiesandImpairmentonSecuritiesArisingDuringPeriodnetoftax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_RealizedGainLossonMarketableSecuritiesandOtherthanTemporaryImpairmentMember
0.1clf_OtherComprehensiveIncomeLossRealizedHoldingGainLossonSecuritiesandImpairmentonSecuritiesArisingDuringPeriodnetoftax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_RealizedGainLossonMarketableSecuritiesandOtherthanTemporaryImpairmentMember
Foreign Currency Translation Adjustment [Member]    
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]    
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax 182.7us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentBeforeTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_ForeignCurrencyTranslationAdjustmentMember
[2] 0us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentBeforeTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_ForeignCurrencyTranslationAdjustmentMember
[2]
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax 0us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_ForeignCurrencyTranslationAdjustmentMember
0us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_ForeignCurrencyTranslationAdjustmentMember
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax 182.7us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_ForeignCurrencyTranslationAdjustmentMember
0us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_ForeignCurrencyTranslationAdjustmentMember
Realized Gain Loss On Derivatives [Member]    
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]    
(Gain) Loss on Derivative Instruments, Net, Pretax 9.0us-gaap_GainLossOnDerivativeInstrumentsNetPretax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_RealizedGainLossOnDerivativesMember
18.5us-gaap_GainLossOnDerivativeInstrumentsNetPretax
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_RealizedGainLossOnDerivativesMember
Tax on Derivative Instruments Gain/Loss Reclassified from Accumulated OCI in to Earnings (2.7)clf_Taxonderivativeinstrumentsgainlossreclassifiedfromaccumulatedociintoearnings
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_RealizedGainLossOnDerivativesMember
(5.7)clf_Taxonderivativeinstrumentsgainlossreclassifiedfromaccumulatedociintoearnings
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_RealizedGainLossOnDerivativesMember
Amount of (gain)/loss recognized in income on derivative 6.3us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_RealizedGainLossOnDerivativesMember
12.8us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_RealizedGainLossOnDerivativesMember
Australian Hedge Contracts [Member] | Realized Gain Loss On Derivatives [Member]    
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]    
Derivative Instruments, (Gain) Loss Reclassified from Accumulated OCI into Income, Effective Portion, Net 9.0us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_AustralianHedgeContractsMember
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_RealizedGainLossOnDerivativesMember
13.0us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_AustralianHedgeContractsMember
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_RealizedGainLossOnDerivativesMember
Canadian Hedge Contracts [Member] | Realized Gain Loss On Derivatives [Member]    
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]    
Derivative Instruments, (Gain) Loss Reclassified from Accumulated OCI into Income, Effective Portion, Net $ 0us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianHedgeContractsMember
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_RealizedGainLossOnDerivativesMember
$ 5.5us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianHedgeContractsMember
/ us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis
= clf_RealizedGainLossOnDerivativesMember
[1] These accumulated other comprehensive income components are included in the computation of net periodic benefit cost. See NOTE 7 - PENSIONS AND OTHER POSTRETIREMENT BENEFITS for further information.
[2] Represents Canadian accumulated currency translation adjustments deconsolidated on January 27, 2015.