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Annual report pursuant to Section 13 and 15(d)

INCOME TAXES INCOME TAXES (Schedule of Effective Rate Reconciliation) (Details)

v2.4.1.9
INCOME TAXES INCOME TAXES (Schedule of Effective Rate Reconciliation) (Details)
In Millions, unless otherwise specified
 3 Months Ended 12 Months Ended
Dec. 31, 2014
USD ($)
Dec. 31, 2014
USD ($)
Dec. 31, 2014
Dec. 31, 2013
USD ($)
Dec. 31, 2013
Dec. 31, 2012
USD ($)
Dec. 31, 2012
Income Tax Contingency [Line Items] Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount Ìý $ (3,361.3)us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate Ìý $ 171.3us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate Ìý $ (175.6)us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate Ìý
Effective Income Tax Rate Reconciliation, Percent Ìý 35.00%us-gaap_EffectiveIncomeTaxRateContinuingOperations 35.00%us-gaap_EffectiveIncomeTaxRateContinuingOperations 35.00%us-gaap_EffectiveIncomeTaxRateContinuingOperations 35.00%us-gaap_EffectiveIncomeTaxRateContinuingOperations 35.00%us-gaap_EffectiveIncomeTaxRateContinuingOperations 35.00%us-gaap_EffectiveIncomeTaxRateContinuingOperations
Foreign Currency Transaction Gain, before Tax Ìý (4.1)us-gaap_ForeignCurrencyTransactionGainBeforeTax Ìý (2.6)us-gaap_ForeignCurrencyTransactionGainBeforeTax Ìý 62.3us-gaap_ForeignCurrencyTransactionGainBeforeTax Ìý
Foreign Currency Transaction Gain Before Tax Percent Ìý 0.00%clf_ForeignCurrencyTransactionGainBeforeTaxPercent 0.00%clf_ForeignCurrencyTransactionGainBeforeTaxPercent (0.50%)clf_ForeignCurrencyTransactionGainBeforeTaxPercent (0.50%)clf_ForeignCurrencyTransactionGainBeforeTaxPercent (12.40%)clf_ForeignCurrencyTransactionGainBeforeTaxPercent (12.40%)clf_ForeignCurrencyTransactionGainBeforeTaxPercent
Non-taxable loss (income) related to noncontrolling interests Ìý 290.1clf_NonTaxableLossIncomeRelatedToNoncontrollingInterests Ìý (1.5)clf_NonTaxableLossIncomeRelatedToNoncontrollingInterests Ìý 61.0clf_NonTaxableLossIncomeRelatedToNoncontrollingInterests Ìý
Non-taxable loss (income) related to noncontrolling interests percent Ìý (3.00%)clf_Nontaxablelossincomerelatedtononcontrollinginterestspercent (3.00%)clf_Nontaxablelossincomerelatedtononcontrollinginterestspercent (0.30%)clf_Nontaxablelossincomerelatedtononcontrollinginterestspercent (0.30%)clf_Nontaxablelossincomerelatedtononcontrollinginterestspercent (12.00%)clf_Nontaxablelossincomerelatedtononcontrollinginterestspercent (12.00%)clf_Nontaxablelossincomerelatedtononcontrollinginterestspercent
Impact Of Tax Law Change Ìý 13.0clf_ImpactOfTaxLawChange Ìý 0clf_ImpactOfTaxLawChange Ìý (357.1)clf_ImpactOfTaxLawChange Ìý
Impact Of Tax Law Change Percent Ìý (0.10%)clf_ImpactOfTaxLawChangePercent (0.10%)clf_ImpactOfTaxLawChangePercent 0.00%clf_ImpactOfTaxLawChangePercent 0.00%clf_ImpactOfTaxLawChangePercent 71.20%clf_ImpactOfTaxLawChangePercent 71.20%clf_ImpactOfTaxLawChangePercent
Income Tax Reconciliation Tax Deduction for percentage depletion in excess of cost depletion Ìý (87.9)clf_IncomeTaxReconciliationTaxDeductionForPercentageDepletionInExcessOfCostDepletion Ìý (97.6)clf_IncomeTaxReconciliationTaxDeductionForPercentageDepletionInExcessOfCostDepletion Ìý (109.1)clf_IncomeTaxReconciliationTaxDeductionForPercentageDepletionInExcessOfCostDepletion Ìý
Income Tax Reconciliation Tax Deduction for percentage depletion in excess of cost depletion percent Ìý 0.90%clf_IncomeTaxReconciliationTaxDeductionforpercentagedepletioninexcessofcostdepletionpercent 0.90%clf_IncomeTaxReconciliationTaxDeductionforpercentagedepletioninexcessofcostdepletionpercent (19.90%)clf_IncomeTaxReconciliationTaxDeductionforpercentagedepletioninexcessofcostdepletionpercent (19.90%)clf_IncomeTaxReconciliationTaxDeductionforpercentagedepletioninexcessofcostdepletionpercent 21.70%clf_IncomeTaxReconciliationTaxDeductionforpercentagedepletioninexcessofcostdepletionpercent 21.70%clf_IncomeTaxReconciliationTaxDeductionforpercentagedepletioninexcessofcostdepletionpercent
Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Amount Ìý 592.0us-gaap_IncomeTaxReconciliationForeignIncomeTaxRateDifferential Ìý (10.2)us-gaap_IncomeTaxReconciliationForeignIncomeTaxRateDifferential Ìý 65.2us-gaap_IncomeTaxReconciliationForeignIncomeTaxRateDifferential Ìý
Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Percent Ìý (6.20%)us-gaap_EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential (6.20%)us-gaap_EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential (2.10%)us-gaap_EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential (2.10%)us-gaap_EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential (13.00%)us-gaap_EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential (13.00%)us-gaap_EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential
Income not subject to tax Ìý (46.5)clf_IncomeNotSubjectToTax Ìý (106.6)clf_IncomeNotSubjectToTax Ìý (108.0)clf_IncomeNotSubjectToTax Ìý
Income not subject to tax percent Ìý 0.50%clf_Incomenotsubjecttotaxpercent 0.50%clf_Incomenotsubjecttotaxpercent (21.80%)clf_Incomenotsubjecttotaxpercent (21.80%)clf_Incomenotsubjecttotaxpercent 21.50%clf_Incomenotsubjecttotaxpercent 21.50%clf_Incomenotsubjecttotaxpercent
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Impairment Losses, Amount Ìý 22.7us-gaap_IncomeTaxReconciliationNondeductibleExpenseImpairmentLosses Ìý 20.5us-gaap_IncomeTaxReconciliationNondeductibleExpenseImpairmentLosses Ìý 202.2us-gaap_IncomeTaxReconciliationNondeductibleExpenseImpairmentLosses Ìý
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Impairment Losses, Percent Ìý (0.20%)us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseImpairmentLosses (0.20%)us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseImpairmentLosses 4.20%us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseImpairmentLosses 4.20%us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseImpairmentLosses (40.30%)us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseImpairmentLosses (40.30%)us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseImpairmentLosses
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount Ìý (43.6)us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes Ìý 5.6us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes Ìý 7.3us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes Ìý
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent Ìý 0.50%us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes 0.50%us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes 1.10%us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes 1.10%us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes (1.50%)us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes (1.50%)us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes
Effective Income Tax Rate Reconciliation, Tax Settlement, Amount Ìý (343.3)us-gaap_IncomeTaxReconciliationTaxSettlements Ìý 0us-gaap_IncomeTaxReconciliationTaxSettlements Ìý 0us-gaap_IncomeTaxReconciliationTaxSettlements Ìý
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent Ìý 3.60%us-gaap_EffectiveIncomeTaxRateReconciliationTaxSettlements 3.60%us-gaap_EffectiveIncomeTaxRateReconciliationTaxSettlements 0.00%us-gaap_EffectiveIncomeTaxRateReconciliationTaxSettlements 0.00%us-gaap_EffectiveIncomeTaxRateReconciliationTaxSettlements 0.00%us-gaap_EffectiveIncomeTaxRateReconciliationTaxSettlements 0.00%us-gaap_EffectiveIncomeTaxRateReconciliationTaxSettlements
Income Tax Reconciliation Manufacturers Deduction Ìý 0clf_IncomeTaxReconciliationManufacturersDeduction Ìý (7.9)clf_IncomeTaxReconciliationManufacturersDeduction Ìý (4.7)clf_IncomeTaxReconciliationManufacturersDeduction Ìý
Income Tax Reconciliation, Manufacturers Deduction Percent Ìý 0.00%clf_IncomeTaxReconciliationManufacturersDeductionPercent 0.00%clf_IncomeTaxReconciliationManufacturersDeductionPercent (1.60%)clf_IncomeTaxReconciliationManufacturersDeductionPercent (1.60%)clf_IncomeTaxReconciliationManufacturersDeductionPercent 0.90%clf_IncomeTaxReconciliationManufacturersDeductionPercent 0.90%clf_IncomeTaxReconciliationManufacturersDeductionPercent
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount Ìý 1,660.6us-gaap_IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance Ìý 73.0us-gaap_IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance Ìý 634.5us-gaap_IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance Ìý
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent Ìý (17.30%)us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance (17.30%)us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance 14.90%us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance 14.90%us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance (126.50%)us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance (126.50%)us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance
Tax Adjustments, Settlements, and Unusual Provisions Ìý 0.2us-gaap_TaxAdjustmentsSettlementsAndUnusualProvisions Ìý 19.6us-gaap_TaxAdjustmentsSettlementsAndUnusualProvisions Ìý (14.8)us-gaap_TaxAdjustmentsSettlementsAndUnusualProvisions Ìý
Tax Adjustments Settlements And Unusual Provisions Percent Ìý 0.00%clf_TaxAdjustmentsSettlementsAndUnusualProvisionsPercent 0.00%clf_TaxAdjustmentsSettlementsAndUnusualProvisionsPercent 5.30%clf_TaxAdjustmentsSettlementsAndUnusualProvisionsPercent 5.30%clf_TaxAdjustmentsSettlementsAndUnusualProvisionsPercent 2.90%clf_TaxAdjustmentsSettlementsAndUnusualProvisionsPercent 2.90%clf_TaxAdjustmentsSettlementsAndUnusualProvisionsPercent
Effective Income Tax Rate Reconciliation, Prior Year Income Taxes, Percent Ìý 0.10%us-gaap_EffectiveIncomeTaxRateReconciliationPriorYearIncomeTaxes (1040000000.00%)us-gaap_EffectiveIncomeTaxRateReconciliationPriorYearIncomeTaxes (3.60%)us-gaap_EffectiveIncomeTaxRateReconciliationPriorYearIncomeTaxes (1140000000.00%)us-gaap_EffectiveIncomeTaxRateReconciliationPriorYearIncomeTaxes 1.10%us-gaap_EffectiveIncomeTaxRateReconciliationPriorYearIncomeTaxes (570000000.00%)us-gaap_EffectiveIncomeTaxRateReconciliationPriorYearIncomeTaxes
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount Ìý 16.5us-gaap_IncomeTaxReconciliationOtherAdjustments Ìý 2.9us-gaap_IncomeTaxReconciliationOtherAdjustments Ìý (1.6)us-gaap_IncomeTaxReconciliationOtherAdjustments Ìý
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent Ìý (0.20%)us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments (0.20%)us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments 0.60%us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments 0.60%us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments 0.40%us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments 0.40%us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments
Income Tax Expense (Benefit) $ (289.7)us-gaap_IncomeTaxExpenseBenefit $ (1,302.0)us-gaap_IncomeTaxExpenseBenefit Ìý $ 55.1us-gaap_IncomeTaxExpenseBenefit Ìý $ 255.9us-gaap_IncomeTaxExpenseBenefit Ìý
Income Tax Expense Benefit Percent Ìý 13.60%clf_IncomeTaxExpenseBenefitPercent 13.60%clf_IncomeTaxExpenseBenefitPercent 11.30%clf_IncomeTaxExpenseBenefitPercent 11.30%clf_IncomeTaxExpenseBenefitPercent (51.00%)clf_IncomeTaxExpenseBenefitPercent (51.00%)clf_IncomeTaxExpenseBenefitPercent