Quarterly report pursuant to Section 13 or 15(d)

DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES (Schedule Of Derivatives Not Designated As Hedging Instruments) (Details)

v2.4.1.9
DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES (Schedule Of Derivatives Not Designated As Hedging Instruments) (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net $ (15.6)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet $ 24.1us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
Foreign Exchange Contract [Member] | Other Nonoperating Income (Expense) [Member]    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net (5.9)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_OtherNonoperatingIncomeExpenseMember 		[1] (0.9)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_OtherNonoperatingIncomeExpenseMember 		[1]
Commodity Contract [Member] | Cost of Sales [Member]    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net (3.6)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember 		0us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember
Customer Supply Agreements [Member] | Product Revenues [Member]    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net 10.1us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CustomerSupplyAgreementsMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesRevenueGoodsNetMember 		27.7us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CustomerSupplyAgreementsMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesRevenueGoodsNetMember
Provisional Pricing Arrangements [Member] | Product Revenues [Member]    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net $ (16.2)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_ProvisionalPricingArrangementsMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesRevenueGoodsNetMember 		$ (2.7)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_ProvisionalPricingArrangementsMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesRevenueGoodsNetMember
[1] At March 31, 2014, the location of the Gain (Loss) Recognized in Income on Derivative for Foreign Exchange Contracts was Cost of goods sold and operating expenses.