Quarterly report pursuant to Section 13 or 15(d)

DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES (Schedule Of Derivative Instruments In Statement Of Financial Position, Fair Value) (Details)

v2.4.1.9
DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES (Schedule Of Derivative Instruments In Statement Of Financial Position, Fair Value) (Details) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Derivatives, Fair Value [Line Items]    
Derivative asset, fair value $ 34.5us-gaap_DerivativeFairValueOfDerivativeAsset $ 63.2us-gaap_DerivativeFairValueOfDerivativeAsset
Derivative liability, fair value 26.5us-gaap_DerivativeFairValueOfDerivativeLiability 41.0us-gaap_DerivativeFairValueOfDerivativeLiability
Designated as Hedging Instrument [Member]    
Derivatives, Fair Value [Line Items]    
Derivative asset, fair value 0us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember 		0us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember
Derivative liability, fair value 0us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember 		21.6us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember
Not Designated as Hedging Instrument [Member]    
Derivatives, Fair Value [Line Items]    
Derivative asset, fair value 34.5us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember 		63.2us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Derivative liability, fair value 26.5us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember 		19.4us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Fair Value, Inputs, Level 2 [Member] | Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Derivative Financial Instruments, Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative asset, fair value 0us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_DerivativeFinancialInstrumentsAssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember 		0us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_DerivativeFinancialInstrumentsAssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember
Fair Value, Inputs, Level 2 [Member] | Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Derivative Financial Instruments, Liabilities [Member]    
Derivatives, Fair Value [Line Items]    
Derivative liability, fair value 0us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember 		21.6us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember
Fair Value, Inputs, Level 2 [Member] | Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Derivative Financial Instruments, Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative asset, fair value 0us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_DerivativeFinancialInstrumentsAssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember 		0us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_DerivativeFinancialInstrumentsAssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Fair Value, Inputs, Level 2 [Member] | Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | Derivative Financial Instruments, Liabilities [Member]    
Derivatives, Fair Value [Line Items]    
Derivative liability, fair value 8.7us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember 		9.9us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Fair Value, Inputs, Level 2 [Member] | Not Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Derivative Financial Instruments, Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative asset, fair value 0us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_DerivativeFinancialInstrumentsAssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember 		0us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_DerivativeFinancialInstrumentsAssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Fair Value, Inputs, Level 2 [Member] | Not Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Derivative Financial Instruments, Liabilities [Member]    
Derivatives, Fair Value [Line Items]    
Derivative asset, fair value 1.6us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember 		0us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
Market Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Customer Supply Agreement [Member] | Derivative Financial Instruments, Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative asset, fair value 34.5us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_DerivativeFinancialInstrumentsAssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CustomerSupplyAgreementMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
/ us-gaap_ValuationTechniqueAxis
= us-gaap_MarketApproachValuationTechniqueMember 		63.2us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_DerivativeFinancialInstrumentsAssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CustomerSupplyAgreementMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
/ us-gaap_ValuationTechniqueAxis
= us-gaap_MarketApproachValuationTechniqueMember
Market Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Customer Supply Agreement [Member] | Derivative Financial Instruments, Liabilities [Member]    
Derivatives, Fair Value [Line Items]    
Derivative liability, fair value 0us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CustomerSupplyAgreementMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
/ us-gaap_ValuationTechniqueAxis
= us-gaap_MarketApproachValuationTechniqueMember 		0us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CustomerSupplyAgreementMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
/ us-gaap_ValuationTechniqueAxis
= us-gaap_MarketApproachValuationTechniqueMember
Market Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Provisional Pricing Arrangements [Member] | Derivative Financial Instruments, Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative asset, fair value 0us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_DerivativeFinancialInstrumentsAssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_ProvisionalPricingArrangementsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
/ us-gaap_ValuationTechniqueAxis
= us-gaap_MarketApproachValuationTechniqueMember 		0us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_DerivativeFinancialInstrumentsAssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_ProvisionalPricingArrangementsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
/ us-gaap_ValuationTechniqueAxis
= us-gaap_MarketApproachValuationTechniqueMember
Market Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Provisional Pricing Arrangements [Member] | Derivative Financial Instruments, Liabilities [Member]    
Derivatives, Fair Value [Line Items]    
Derivative liability, fair value $ 16.2us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_ProvisionalPricingArrangementsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
/ us-gaap_ValuationTechniqueAxis
= us-gaap_MarketApproachValuationTechniqueMember 		$ 9.5us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_ProvisionalPricingArrangementsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
/ us-gaap_ValuationTechniqueAxis
= us-gaap_MarketApproachValuationTechniqueMember