Quarterly report pursuant to Section 13 or 15(d)

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

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Betfred
 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 Betfredlocation of the Gain (Loss) Recognized in Income on Derivative for Foreign Exchange Contracts was Cost of goods sold and operating expenses.