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INCOME TAXES INCOME TAXES (Schedule of Deferred Tax Assets and Liabilities) (Details) (USD $)
In Millions, unless otherwise specified |
Dec. 31, 2014
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Dec. 31, 2013
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| Income Tax Contingency [Line Items] | ||
| Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Pensions | $ 108.3us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPensions | $ 88.4us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPensions |
| Deferred Tax Assets, MMRT Starting Base Allowance | 0clf_DeferredTaxAssetsMmrtStartingBaseAllowance | 300.3clf_DeferredTaxAssetsMmrtStartingBaseAllowance |
| Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Postretirement Benefits | 63.0us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPostretirementBenefits | 58.0us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPostretirementBenefits |
| Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax | 267.7us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsAlternativeMinimumTax | 299.2us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsAlternativeMinimumTax |
| Deferred Tax Assets Development Costs | 6.0clf_DeferredTaxAssetsDevelopmentCosts | 0clf_DeferredTaxAssetsDevelopmentCosts |
| Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Asset Retirement Obligations | 48.9us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsAssetRetirementObligations | 61.7us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsAssetRetirementObligations |
| Deferred Tax Assets, Operating Loss Carryforwards | 1,083.5us-gaap_DeferredTaxAssetsOperatingLossCarryforwards | 524.4us-gaap_DeferredTaxAssetsOperatingLossCarryforwards |
| Deferred Tax Assets, Inventory | 32.3us-gaap_DeferredTaxAssetsInventory | 16.4us-gaap_DeferredTaxAssetsInventory |
| Deferred Tax Assets, Property, Plant and Equipment | 901.6us-gaap_DeferredTaxAssetsPropertyPlantAndEquipment | 56.0us-gaap_DeferredTaxAssetsPropertyPlantAndEquipment |
| Deferred Tax Assets, State Taxes | 41.9us-gaap_DeferredTaxAssetsStateTaxes | 0us-gaap_DeferredTaxAssetsStateTaxes |
| Deferred Tax Assets Leasing Arrangements | 14.1clf_DeferredTaxAssetsLeasingArrangements | 31.9clf_DeferredTaxAssetsLeasingArrangements |
| Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Other | 153.6us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsOther | 138.3us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsOther |
| Deferred Tax Assets, Gross | 2,720.9us-gaap_DeferredTaxAssetsGross | 1,574.6us-gaap_DeferredTaxAssetsGross |
| Deferred Tax Assets, Valuation Allowance | (2,224.5)us-gaap_DeferredTaxAssetsValuationAllowance | (864.1)us-gaap_DeferredTaxAssetsValuationAllowance |
| Deferred Tax Assets, Net of Valuation Allowance | 496.4us-gaap_DeferredTaxAssetsNet | 710.5us-gaap_DeferredTaxAssetsNet |
| Deferred Tax Liabilities, Property, Plant and Equipment | (20.0)us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment | (1,400.8)us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment |
| Deferred Tax Liabilities Investment In Ventures | (198.0)clf_DeferredTaxLiabilitiesInvestmentInVentures | (196.4)clf_DeferredTaxLiabilitiesInvestmentInVentures |
| Deferred Tax Liabilities, Intangible Assets | (7.3)us-gaap_DeferredTaxLiabilitiesGoodwillAndIntangibleAssetsIntangibleAssets | (33.5)us-gaap_DeferredTaxLiabilitiesGoodwillAndIntangibleAssetsIntangibleAssets |
| Deferred Tax Liabilities Income Tax Uncertainties | (49.5)clf_DeferredTaxLiabilitiesIncomeTaxUncertainties | (48.5)clf_DeferredTaxLiabilitiesIncomeTaxUncertainties |
| Deferred Tax Liabilities, Tax Deferred Income | (16.6)us-gaap_DeferredTaxLiabilitiesTaxDeferredIncome | (12.8)us-gaap_DeferredTaxLiabilitiesTaxDeferredIncome |
| Deferred Tax Liabilities Other Assets | (80.2)clf_DeferredTaxLiabilitiesOtherAssets | (93.0)clf_DeferredTaxLiabilitiesOtherAssets |
| Deferred Tax Liabilities, Net | (371.6)us-gaap_DeferredTaxLiabilities | (1,785.0)us-gaap_DeferredTaxLiabilities |
| Deferred Tax Assets, Net | $ 124.8us-gaap_DeferredTaxAssetsLiabilitiesNet | $ (1,074.5)us-gaap_DeferredTaxAssetsLiabilitiesNet |
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- Definition
The tax effect as of the balance sheet date of the amount of the estimated future tax deductions attributable to capitalized development expenses. No definition available.
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- Definition
The tax effect as of the balance sheet date of the amount of the estimated future tax deductions attributable lease liabilities. No definition available.
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- Definition
Deferred Tax Assets, MMRT Starting Base Allowance No definition available.
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- Definition
The amount as of the balance sheet date of the estimated future tax effects attributable to income tax uncertainties. No definition available.
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- Definition
Deferred Tax Liabilities Investment In Ventures No definition available.
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- Definition
The tax effect as of the balance sheet date attributable to other assets that will result in future taxable income exceeding future accounting income. No definition available.
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- Definition
Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from inventory. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards, net of deferred tax liability attributable to taxable temporary differences. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from property, plant, and equipment. No definition available.
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- Definition
Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from state taxes. No definition available.
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- Definition
Amount before allocation of valuation allowances of deferred tax asset attributable to deductible alternative minimum tax credit carryforwards. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from pension benefits. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from postretirement benefits. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from asset retirement obligations. An asset retirement obligation is a legal obligation associated with the disposal or retirement from service of a tangible long-lived asset. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from other reserves and accruals not separately disclosed. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount of deferred tax liability attributable to taxable temporary differences net of deferred tax asset attributable to deductible temporary differences and carryforwards after valuation allowances. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount of deferred tax liability attributable to taxable temporary differences from intangible assets other than goodwill. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount of deferred tax liability attributable to taxable temporary differences from property, plant, and equipment. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount of deferred tax liability attributable to taxable temporary differences from tax deferred revenue or other income not separately disclosed. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Details
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