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Quarterly report pursuant to Section 13 or 15(d)

FAIR VALUE OF FINANCIAL INSTRUMENTS FAIR VALUE OF FINANCIAL INSTRUMENTS (Fair Value Measurements, Nonrecurring) (Details)

v2.4.1.9
FAIR VALUE OF FINANCIAL INSTRUMENTS FAIR VALUE OF FINANCIAL INSTRUMENTS (Fair Value Measurements, Nonrecurring) (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended 12 Months Ended
Mar. 31, 2015
Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Goodwill, Impairment Loss $ 0us-gaap_GoodwillImpairmentLoss $ 73.5us-gaap_GoodwillImpairmentLoss
Assets, Fair Value Disclosure, Nonrecurring 397.2us-gaap_AssetsFairValueDisclosureNonrecurring 79.4us-gaap_AssetsFairValueDisclosureNonrecurring
Impairment of goodwill and other long-lived assets 269.5clf_ImpairmentCharges 644.7clf_ImpairmentCharges
Fair Value, Inputs, Level 1 [Member] Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Assets, Fair Value Disclosure, Nonrecurring 0us-gaap_AssetsFairValueDisclosureNonrecurring
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
0us-gaap_AssetsFairValueDisclosureNonrecurring
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Fair Value, Inputs, Level 2 [Member] Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Assets, Fair Value Disclosure, Nonrecurring 397.2us-gaap_AssetsFairValueDisclosureNonrecurring
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
0us-gaap_AssetsFairValueDisclosureNonrecurring
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Fair Value, Inputs, Level 3 [Member] Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Assets, Fair Value Disclosure, Nonrecurring 0us-gaap_AssetsFairValueDisclosureNonrecurring
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
79.4us-gaap_AssetsFairValueDisclosureNonrecurring
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Global Exploration Investment in Venture [Member] Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Equity Method Investments, Fair Value Disclosure Ìý 0us-gaap_EquityMethodInvestmentsFairValueDisclosure
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_GlobalExplorationInvestmentinVentureMember
Equity Method Investment, Other than Temporary Impairment Ìý 9.2us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_GlobalExplorationInvestmentinVentureMember
Global Exploration Investment in Venture [Member] | Fair Value, Inputs, Level 1 [Member] Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Equity Method Investments, Fair Value Disclosure Ìý 0us-gaap_EquityMethodInvestmentsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_GlobalExplorationInvestmentinVentureMember
Global Exploration Investment in Venture [Member] | Fair Value, Inputs, Level 2 [Member] Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Equity Method Investments, Fair Value Disclosure Ìý 0us-gaap_EquityMethodInvestmentsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_GlobalExplorationInvestmentinVentureMember
Global Exploration Investment in Venture [Member] | Fair Value, Inputs, Level 3 [Member] Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Equity Method Investments, Fair Value Disclosure Ìý 0us-gaap_EquityMethodInvestmentsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_GlobalExplorationInvestmentinVentureMember
Asia Pacific Iron Ore [Member] Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Goodwill, Fair Value Disclosure Ìý 0us-gaap_GoodwillFairValueDisclosure
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember
Goodwill, Impairment Loss Ìý 73.5us-gaap_GoodwillImpairmentLoss
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember
Asia Pacific Iron Ore [Member] | Fair Value, Inputs, Level 1 [Member] Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Goodwill, Fair Value Disclosure Ìý 0us-gaap_GoodwillFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember
Asia Pacific Iron Ore [Member] | Fair Value, Inputs, Level 2 [Member] Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Goodwill, Fair Value Disclosure Ìý 0us-gaap_GoodwillFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember
Asia Pacific Iron Ore [Member] | Fair Value, Inputs, Level 3 [Member] Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Goodwill, Fair Value Disclosure Ìý 0us-gaap_GoodwillFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember
Other Reporting Units [Member] Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Property, Plant, and Equipment, Fair Value Disclosure Ìý 0us-gaap_PropertyPlantAndEquipmentFairValueDisclosure
/ clf_ReportingUnitAxis
= clf_OtherReportingUnitsMember
Tangible Asset Impairment Charges Ìý 11.3us-gaap_TangibleAssetImpairmentCharges
/ clf_ReportingUnitAxis
= clf_OtherReportingUnitsMember
Other Reporting Units [Member] | Fair Value, Inputs, Level 1 [Member] Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Property, Plant, and Equipment, Fair Value Disclosure Ìý 0us-gaap_PropertyPlantAndEquipmentFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ clf_ReportingUnitAxis
= clf_OtherReportingUnitsMember
Other Reporting Units [Member] | Fair Value, Inputs, Level 2 [Member] Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Property, Plant, and Equipment, Fair Value Disclosure Ìý 0us-gaap_PropertyPlantAndEquipmentFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ clf_ReportingUnitAxis
= clf_OtherReportingUnitsMember
Other Reporting Units [Member] | Fair Value, Inputs, Level 3 [Member] Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Property, Plant, and Equipment, Fair Value Disclosure Ìý 0us-gaap_PropertyPlantAndEquipmentFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ clf_ReportingUnitAxis
= clf_OtherReportingUnitsMember
Asia Pacific [Member] | Asia Pacific Iron Ore [Member] | Fair Value, Inputs, Level 2 [Member] Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Property, Plant, and Equipment, Fair Value Disclosure Ìý 0us-gaap_PropertyPlantAndEquipmentFairValueDisclosure
/ clf_AssetgroupAxis
= us-gaap_AsiaPacificMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember
Finite-lived Intangible Assets, Fair Value Disclosure Ìý 0us-gaap_FiniteLivedIntangibleAssetsFairValueDisclosure
/ clf_AssetgroupAxis
= us-gaap_AsiaPacificMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember
Asia Pacific Iron Ore [Member] | Asia Pacific Iron Ore [Member] Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Property, Plant, and Equipment, Fair Value Disclosure Ìý 72.4us-gaap_PropertyPlantAndEquipmentFairValueDisclosure
/ clf_AssetgroupAxis
= clf_AsiaPacificIronOreMember
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember
Tangible Asset Impairment Charges Ìý 526.5us-gaap_TangibleAssetImpairmentCharges
/ clf_AssetgroupAxis
= clf_AsiaPacificIronOreMember
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember
Other Asset Impairment Charges Ìý 24.2us-gaap_ImpairmentOfIntangibleAssetsExcludingGoodwill
/ clf_AssetgroupAxis
= clf_AsiaPacificIronOreMember
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember
Finite-lived Intangible Assets, Fair Value Disclosure Ìý 7.0us-gaap_FiniteLivedIntangibleAssetsFairValueDisclosure
/ clf_AssetgroupAxis
= clf_AsiaPacificIronOreMember
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember
Asia Pacific Iron Ore [Member] | Asia Pacific Iron Ore [Member] | Fair Value, Inputs, Level 1 [Member] Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Property, Plant, and Equipment, Fair Value Disclosure Ìý 0us-gaap_PropertyPlantAndEquipmentFairValueDisclosure
/ clf_AssetgroupAxis
= clf_AsiaPacificIronOreMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember
Finite-lived Intangible Assets, Fair Value Disclosure Ìý 0us-gaap_FiniteLivedIntangibleAssetsFairValueDisclosure
/ clf_AssetgroupAxis
= clf_AsiaPacificIronOreMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember
Asia Pacific Iron Ore [Member] | Asia Pacific Iron Ore [Member] | Fair Value, Inputs, Level 3 [Member] Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Property, Plant, and Equipment, Fair Value Disclosure Ìý 72.4us-gaap_PropertyPlantAndEquipmentFairValueDisclosure
/ clf_AssetgroupAxis
= clf_AsiaPacificIronOreMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember
Finite-lived Intangible Assets, Fair Value Disclosure Ìý 7.0us-gaap_FiniteLivedIntangibleAssetsFairValueDisclosure
/ clf_AssetgroupAxis
= clf_AsiaPacificIronOreMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ clf_ReportingUnitAxis
= clf_AsiaPacificIronOreMember
Five hundred Forty-four Million Seven Point Seven Five Twenty Twenty Second Lien Notes [Member] Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Debt Instrument, Fair Value Disclosure 397.2us-gaap_DebtInstrumentFairValue
/ us-gaap_DebtInstrumentAxis
= clf_FivehundredFortyfourMillionSevenPointSevenFiveTwentyTwentySecondLienNotesMember
Ìý
Gain on new debt issued 269.5clf_Gainonnewdebtissued
/ us-gaap_DebtInstrumentAxis
= clf_FivehundredFortyfourMillionSevenPointSevenFiveTwentyTwentySecondLienNotesMember
Ìý
Five hundred Forty-four Million Seven Point Seven Five Twenty Twenty Second Lien Notes [Member] | Fair Value, Inputs, Level 1 [Member] Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Debt Instrument, Fair Value Disclosure 0us-gaap_DebtInstrumentFairValue
/ us-gaap_DebtInstrumentAxis
= clf_FivehundredFortyfourMillionSevenPointSevenFiveTwentyTwentySecondLienNotesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Ìý
Five hundred Forty-four Million Seven Point Seven Five Twenty Twenty Second Lien Notes [Member] | Fair Value, Inputs, Level 2 [Member] Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Debt Instrument, Fair Value Disclosure 397.2us-gaap_DebtInstrumentFairValue
/ us-gaap_DebtInstrumentAxis
= clf_FivehundredFortyfourMillionSevenPointSevenFiveTwentyTwentySecondLienNotesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
0us-gaap_DebtInstrumentFairValue
/ us-gaap_DebtInstrumentAxis
= clf_FivehundredFortyfourMillionSevenPointSevenFiveTwentyTwentySecondLienNotesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Five hundred Forty-four Million Seven Point Seven Five Twenty Twenty Second Lien Notes [Member] | Fair Value, Inputs, Level 3 [Member] Ìý Ìý
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Ìý Ìý
Debt Instrument, Fair Value Disclosure $ 0us-gaap_DebtInstrumentFairValue
/ us-gaap_DebtInstrumentAxis
= clf_FivehundredFortyfourMillionSevenPointSevenFiveTwentyTwentySecondLienNotesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
Ìý