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Annual report pursuant to Section 13 and 15(d)

DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES (Narrative) (Details)

v2.4.1.9
DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES (Narrative) (Details) (USD $)
 12 Months Ended 9 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Sep. 30, 2013
Derivative [Line Items] Ìý Ìý Ìý Ìý
Current Fiscal Year End Date --12-31 Ìý Ìý Ìý
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net $ (28,200,000)us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet $ (51,700,000)us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet $ 25,600,000us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet Ìý
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net (31,000,000)us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet (22,100,000)us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet 18,100,000us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet Ìý
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net 159,100,000us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet 141,400,000us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet 163,200,000us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet Ìý
Accounts receivable, net 205,600,000us-gaap_AccountsReceivableNetCurrent 270,000,000us-gaap_AccountsReceivableNetCurrent Ìý Ìý
Canadian Dollar Foreign Exchange Contracts Hedge Prior to De Designation [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net (14,300,000)us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianDollarForeignExchangeContractsHedgePriortoDeDesignationMember 		(4,100,000)us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianDollarForeignExchangeContractsHedgePriortoDeDesignationMember 		0us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianDollarForeignExchangeContractsHedgePriortoDeDesignationMember 		Ìý
Canadian Dollar Foreign Exchange Contracts Hedge Prior to De Designation [Member] | Cost of Sales [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net (17,700,000)us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianDollarForeignExchangeContractsHedgePriortoDeDesignationMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember 		(1,900,000)us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianDollarForeignExchangeContractsHedgePriortoDeDesignationMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember 		0us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianDollarForeignExchangeContractsHedgePriortoDeDesignationMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember 		Ìý
Canadian Dollar Foreign Exchange Contracts Hedge De Designated [Member] [Member] | Not Designated as Hedging Instrument [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Derivative, Notional Amount 0invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianDollarForeignExchangeContractsHedgeDeDesignatedMemberMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember 		Ìý Ìý Ìý
Canadian Dollar Foreign Exchange Contracts Hedge De Designated [Member] [Member] | Not Designated as Hedging Instrument [Member] | Accumulated Other Comprehensive Income (Loss) [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Amount that will be reclassified to product revenues in the next 12 months upon settlement of the related contracts 0us-gaap_ForeignCurrencyCashFlowHedgeGainLossToBeReclassifiedDuringNext12Months
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_AccumulatedOtherComprehensiveIncomeMember
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianDollarForeignExchangeContractsHedgeDeDesignatedMemberMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember 		Ìý Ìý Ìý
Foreign Exchange Contract [Member] | Cost of Sales [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net (16,900,000)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember 		Ìý 0us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember 		Ìý
Australian Dollar Foreign Exchange Contract Hedge Designation [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net (13,900,000)us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_AustralianDollarForeignExchangeContractHedgeDesignationMember 		(34,700,000)us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_AustralianDollarForeignExchangeContractHedgeDesignationMember 		20,200,000us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_AustralianDollarForeignExchangeContractHedgeDesignationMember 		Ìý
Australian Dollar Foreign Exchange Contract Hedge Designation [Member] | Product Revenues [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net (13,200,000)us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_AustralianDollarForeignExchangeContractHedgeDesignationMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesRevenueGoodsNetMember 		(11,900,000)us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_AustralianDollarForeignExchangeContractHedgeDesignationMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesRevenueGoodsNetMember 		14,800,000us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_AustralianDollarForeignExchangeContractHedgeDesignationMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesRevenueGoodsNetMember 		Ìý
Australian Dollar Foreign Exchange Contract Hedge Designation [Member] | Designated as Hedging Instrument [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Derivative, Notional Amount 220,000,000invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_AustralianDollarForeignExchangeContractHedgeDesignationMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember 		323,000,000invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_AustralianDollarForeignExchangeContractHedgeDesignationMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember 		Ìý Ìý
Australian Dollar Foreign Exchange Contract Hedge Designation [Member] | Designated as Hedging Instrument [Member] | Accumulated Other Comprehensive Income (Loss) [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Amount that will be reclassified to product revenues in the next 12 months upon settlement of the related contracts (15,100,000)us-gaap_ForeignCurrencyCashFlowHedgeGainLossToBeReclassifiedDuringNext12Months
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_AccumulatedOtherComprehensiveIncomeMember
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_AustralianDollarForeignExchangeContractHedgeDesignationMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember 		Ìý Ìý Ìý
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net 0us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianDollarForeignExchangeContractsHedgeDesignationMember 		(12,900,000)us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianDollarForeignExchangeContractsHedgeDesignationMember 		6,700,000us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianDollarForeignExchangeContractsHedgeDesignationMember 		Ìý
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member] | Cost of Sales [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net 0us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianDollarForeignExchangeContractsHedgeDesignationMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember 		(8,200,000)us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianDollarForeignExchangeContractsHedgeDesignationMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember 		3,300,000us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianDollarForeignExchangeContractsHedgeDesignationMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember 		Ìý
Canadian Dollar Foreign Exchange Contracts Hedge Designation [Member] | Designated as Hedging Instrument [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Derivative, Notional Amount 0invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianDollarForeignExchangeContractsHedgeDesignationMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember 		285,900,000invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianDollarForeignExchangeContractsHedgeDesignationMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember 		Ìý Ìý
Interest Rate Swap [Member] | Other Nonoperating Income (Expense) [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Gain (Loss) on Fair Value Hedge Ineffectiveness, Net 300,000us-gaap_GainLossOnFairValueHedgeIneffectivenessNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_OtherNonoperatingIncomeExpenseMember 		Ìý Ìý 100,000us-gaap_GainLossOnFairValueHedgeIneffectivenessNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_OtherNonoperatingIncomeExpenseMember
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Derivative, Notional Amount 250,000,000invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember 		Ìý Ìý Ìý
Treasury Lock [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net Ìý Ìý (1,300,000)us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_TreasuryLockMember 		Ìý
Treasury Lock [Member] | Other Nonoperating Income (Expense) [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net (100,000)us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_TreasuryLockMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_OtherNonoperatingIncomeExpenseMember 		(100,000)us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_TreasuryLockMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_OtherNonoperatingIncomeExpenseMember 		0us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_TreasuryLockMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_OtherNonoperatingIncomeExpenseMember 		Ìý
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 		(400,000)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_TreasuryLockMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_OtherNonoperatingIncomeExpenseMember 		Ìý
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months (100,000)us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_TreasuryLockMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_OtherNonoperatingIncomeExpenseMember 		Ìý Ìý Ìý
Treasury Lock [Member] | Designated as Hedging Instrument [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Derivative, Notional Amount Ìý Ìý 200,000,000invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_TreasuryLockMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember 		Ìý
Treasury Lock [Member] | Designated as Hedging Instrument [Member] | Accumulated Other Comprehensive Income (Loss) [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net Ìý (1,300,000)us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_AccumulatedOtherComprehensiveIncomeMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_TreasuryLockMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_DesignatedAsHedgingInstrumentMember 		Ìý Ìý
Customer Supply Agreement [Member] | Not Designated as Hedging Instrument [Member] | Product Revenues [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Amount of gain/(loss) recognized in income on derivative 187,800,000us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CustomerSupplyAgreementMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesRevenueGoodsNetMember 		149,200,000us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CustomerSupplyAgreementMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesRevenueGoodsNetMember 		171,400,000us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CustomerSupplyAgreementMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesRevenueGoodsNetMember 		Ìý
Customer Supply Agreement [Member] | Not Designated as Hedging Instrument [Member] | Other Current Assets [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Derivative assets 63,200,000us-gaap_DerivativeAssetsCurrent
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_OtherCurrentAssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CustomerSupplyAgreementMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember 		55,800,000us-gaap_DerivativeAssetsCurrent
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_OtherCurrentAssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CustomerSupplyAgreementMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember 		Ìý Ìý
Provisional Pricing Arrangements [Member] | Product Revenues [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net (11,800,000)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_ProvisionalPricingArrangementsMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesRevenueGoodsNetMember 		(7,200,000)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_ProvisionalPricingArrangementsMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesRevenueGoodsNetMember 		(7,800,000)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_ProvisionalPricingArrangementsMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesRevenueGoodsNetMember 		Ìý
Provisional Pricing Arrangements [Member] | Not Designated as Hedging Instrument [Member] | U.S. Iron Ore, Eastern Canadian Iron Ore And Asia Pacific Iron Ore [Member] | Product Revenues [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Amount of gain/(loss) recognized in income on derivative (11,800,000)us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_ProvisionalPricingArrangementsMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreEasternCanadianIronOreAndAsiaPacificIronOreMember 		(7,200,000)us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_ProvisionalPricingArrangementsMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreEasternCanadianIronOreAndAsiaPacificIronOreMember 		Ìý Ìý
Provisional Pricing Arrangements [Member] | Not Designated as Hedging Instrument [Member] | U.S. Iron Ore, Eastern Canadian Iron Ore And Asia Pacific Iron Ore [Member] | Other Current Assets [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Derivative assets 0us-gaap_DerivativeAssetsCurrent
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_OtherCurrentAssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_ProvisionalPricingArrangementsMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreEasternCanadianIronOreAndAsiaPacificIronOreMember 		3,100,000us-gaap_DerivativeAssetsCurrent
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_OtherCurrentAssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_ProvisionalPricingArrangementsMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreEasternCanadianIronOreAndAsiaPacificIronOreMember 		Ìý Ìý
Provisional Pricing Arrangements [Member] | Not Designated as Hedging Instrument [Member] | U.S. Iron Ore, Eastern Canadian Iron Ore And Asia Pacific Iron Ore [Member] | Other Current Liabilities [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Derivative liabilities 11,800,000us-gaap_DerivativeLiabilitiesCurrent
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_OtherCurrentLiabilitiesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_ProvisionalPricingArrangementsMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreEasternCanadianIronOreAndAsiaPacificIronOreMember 		10,300,000us-gaap_DerivativeLiabilitiesCurrent
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_OtherCurrentLiabilitiesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_ProvisionalPricingArrangementsMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreEasternCanadianIronOreAndAsiaPacificIronOreMember 		Ìý Ìý
Provisional Pricing Arrangements [Member] | Not Designated as Hedging Instrument [Member] | U.S. Iron Ore and Eastern Canadian Iron Ore [Member] | Product Revenues [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Amount of gain/(loss) recognized in income on derivative Ìý Ìý (7,800,000)us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_ProvisionalPricingArrangementsMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreAndEasternCanadianIronOreMember 		Ìý
$500 Million 3.95% 2018 Senior Notes [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Debt Instrument, Face Amount 500,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= clf_FiveHundredMillionThreePointNineFiveTwoThousandEighteenSeniorNoteMember 		500,000,000.0us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= clf_FiveHundredMillionThreePointNineFiveTwoThousandEighteenSeniorNoteMember 		Ìý Ìý
Bloom Lake [Member] | Canadian Dollar Foreign Exchange Contracts Hedge Prior to De Designation [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net (9,900,000)us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianDollarForeignExchangeContractsHedgePriortoDeDesignationMember
/ clf_ReportingUnitAxis
= clf_BloomLakeMember 		Ìý Ìý Ìý
Bloom Lake [Member] | Canadian Dollar Foreign Exchange Contracts Hedge De Designated [Member] [Member] | Not Designated as Hedging Instrument [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Derivative, Notional Amount 183,000,000invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianDollarForeignExchangeContractsHedgeDeDesignatedMemberMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
/ clf_ReportingUnitAxis
= clf_BloomLakeMember 		Ìý Ìý Ìý
Bloom Lake [Member] | Canadian Dollar Foreign Exchange Contracts Hedge De Designated [Member] [Member] | Not Designated as Hedging Instrument [Member] | Accumulated Other Comprehensive Income (Loss) [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Amount that will be reclassified to product revenues in the next 12 months upon settlement of the related contracts 0us-gaap_ForeignCurrencyCashFlowHedgeGainLossToBeReclassifiedDuringNext12Months
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_AccumulatedOtherComprehensiveIncomeMember
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianDollarForeignExchangeContractsHedgeDeDesignatedMemberMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
/ clf_ReportingUnitAxis
= clf_BloomLakeMember 		Ìý Ìý Ìý
Bloom Lake [Member] | Foreign Exchange Contract [Member] | Cost of Sales [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net (7,300,000)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember
/ clf_ReportingUnitAxis
= clf_BloomLakeMember 		Ìý Ìý Ìý
Wabush and Cliffs Chromite Ontario and Cliffs Chromite Far North [Member] | Canadian Dollar Foreign Exchange Contracts Hedge Prior to De Designation [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net (500,000)us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianDollarForeignExchangeContractsHedgePriortoDeDesignationMember
/ clf_ReportingUnitAxis
= clf_WabushandCliffsChromiteOntarioandCliffsChromiteFarNorthMember 		Ìý Ìý Ìý
Wabush and Cliffs Chromite Ontario and Cliffs Chromite Far North [Member] | Canadian Dollar Foreign Exchange Contracts Hedge De Designated [Member] [Member] | Not Designated as Hedging Instrument [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Derivative, Notional Amount Ìý 74,800,000invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianDollarForeignExchangeContractsHedgeDeDesignatedMemberMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
/ clf_ReportingUnitAxis
= clf_WabushandCliffsChromiteOntarioandCliffsChromiteFarNorthMember 		Ìý Ìý
Wabush and Cliffs Chromite Ontario and Cliffs Chromite Far North [Member] | Canadian Dollar Foreign Exchange Contracts Hedge De Designated [Member] [Member] | Not Designated as Hedging Instrument [Member] | Accumulated Other Comprehensive Income (Loss) [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Amount that will be reclassified to product revenues in the next 12 months upon settlement of the related contracts 0us-gaap_ForeignCurrencyCashFlowHedgeGainLossToBeReclassifiedDuringNext12Months
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_AccumulatedOtherComprehensiveIncomeMember
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianDollarForeignExchangeContractsHedgeDeDesignatedMemberMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember
/ clf_ReportingUnitAxis
= clf_WabushandCliffsChromiteOntarioandCliffsChromiteFarNorthMember 		Ìý Ìý Ìý
Wabush and Cliffs Chromite Ontario and Cliffs Chromite Far North [Member] | Foreign Exchange Contract [Member] | Cost of Sales [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net 3,300,000us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember
/ clf_ReportingUnitAxis
= clf_WabushandCliffsChromiteOntarioandCliffsChromiteFarNorthMember 		(600,000)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_ForeignExchangeContractMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember
/ clf_ReportingUnitAxis
= clf_WabushandCliffsChromiteOntarioandCliffsChromiteFarNorthMember 		Ìý Ìý
Wabush [Member] | Canadian Dollar Foreign Exchange Contracts Hedge Prior to De Designation [Member] Ìý Ìý Ìý Ìý
Derivative [Line Items] Ìý Ìý Ìý Ìý
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net Ìý $ (1,900,000)us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet
/ us-gaap_DerivativeInstrumentRiskAxis
= clf_CanadianDollarForeignExchangeContractsHedgePriortoDeDesignationMember
/ clf_ReportingUnitAxis
= clf_WabushMember 		Ìý Ìý