Annual report pursuant to Section 13 and 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
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]      
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net $ 159.1us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet $ 141.4us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet $ 163.2us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
Foreign Exchange Contract [Member] | Cost of Sales [Member]      
Derivative Instruments, Gain (Loss) [Line Items]      
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net (16.9)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember
  0us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember
Foreign Exchange Contract [Member] | Other Income (Expense) [Member]      
Derivative Instruments, Gain (Loss) [Line Items]      
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net 0us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_OtherIncomeMember
0us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_OtherIncomeMember
0.3us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_OtherIncomeMember
Foreign Exchange Contract [Member] | Discontinued Operations [Member]      
Derivative Instruments, Gain (Loss) [Line Items]      
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net 0us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SegmentDiscontinuedOperationsMember
0us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SegmentDiscontinuedOperationsMember
(0.3)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SegmentDiscontinuedOperationsMember
Treasury Lock [Member] | Other Nonoperating Income (Expense) [Member]      
Derivative Instruments, Gain (Loss) [Line Items]      
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net 0us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_TreasuryLockMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_OtherNonoperatingIncomeExpenseMember
0us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_TreasuryLockMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_OtherNonoperatingIncomeExpenseMember
(0.4)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_TreasuryLockMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_OtherNonoperatingIncomeExpenseMember
Customer Supply Agreements [Member] | Product Revenues [Member]      
Derivative Instruments, Gain (Loss) [Line Items]      
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net 187.8us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CustomerSupplyAgreementsMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesRevenueGoodsNetMember
149.2us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CustomerSupplyAgreementsMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesRevenueGoodsNetMember
171.4us-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 $ (11.8)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_ProvisionalPricingArrangementsMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesRevenueGoodsNetMember
$ (7.2)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_ProvisionalPricingArrangementsMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesRevenueGoodsNetMember
$ (7.8)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_ProvisionalPricingArrangementsMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesRevenueGoodsNetMember