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FAIR VALUE OF FINANCIAL INSTRUMENTS (Narrative) (Details) (USD $)
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3 Months Ended | 12 Months Ended |
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Mar. 31, 2015
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Dec. 31, 2014
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| Fair Value, Assets And Liabilities Components [Line Items] | ||
| Management Estimate of 62% Fe | 62.00%clf_ManagementEstimateOf62Fe | |
| Goodwill, Impairment Loss | $ 0us-gaap_GoodwillImpairmentLoss | $ 73,500,000us-gaap_GoodwillImpairmentLoss |
| Other Asset Impairment Charges | 562,000,000us-gaap_OtherAssetImpairmentCharges | |
| Global Exploration Investment in Venture [Member] | ||
| Fair Value, Assets And Liabilities Components [Line Items] | ||
| Equity Method Investments, Fair Value Disclosure |
0us-gaap_EquityMethodInvestmentsFairValueDisclosure / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = clf_GlobalExplorationInvestmentinVentureMember |
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| Equity Method Investment, Other than Temporary Impairment |
9,200,000us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = clf_GlobalExplorationInvestmentinVentureMember |
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| Asia Pacific Iron Ore [Member] | ||
| Fair Value, Assets And Liabilities Components [Line Items] | ||
| Goodwill, Impairment Loss |
73,500,000us-gaap_GoodwillImpairmentLoss / clf_ReportingUnitAxis = clf_AsiaPacificIronOreMember |
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| Five hundred Forty-four Million Seven Point Seven Five Twenty Twenty Second Lien Notes [Member] | ||
| Fair Value, Assets And Liabilities Components [Line Items] | ||
| Debt Instrument, Par Value |
544,200,000clf_DebtInstrumentParValue / us-gaap_DebtInstrumentAxis = clf_FivehundredFortyfourMillionSevenPointSevenFiveTwentyTwentySecondLienNotesMember |
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| Debt Instrument, Fair Value Disclosure |
397,200,000us-gaap_DebtInstrumentFairValue / us-gaap_DebtInstrumentAxis = clf_FivehundredFortyfourMillionSevenPointSevenFiveTwentyTwentySecondLienNotesMember |
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| Stated interest rate |
7.75%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = clf_FivehundredFortyfourMillionSevenPointSevenFiveTwentyTwentySecondLienNotesMember |
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| Debt discount |
0.27clf_Debtdiscount / us-gaap_DebtInstrumentAxis = clf_FivehundredFortyfourMillionSevenPointSevenFiveTwentyTwentySecondLienNotesMember |
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| Debt Instrument, Unamortized Discount |
147,000,000us-gaap_DebtInstrumentUnamortizedDiscount / us-gaap_DebtInstrumentAxis = clf_FivehundredFortyfourMillionSevenPointSevenFiveTwentyTwentySecondLienNotesMember |
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| Fair Value, Inputs, Level 2 [Member] | Global Exploration Investment in Venture [Member] | ||
| Fair Value, Assets And Liabilities Components [Line Items] | ||
| Equity Method Investments, Fair Value Disclosure |
0us-gaap_EquityMethodInvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = clf_GlobalExplorationInvestmentinVentureMember |
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| Fair Value, Inputs, Level 2 [Member] | Five hundred Forty-four Million Seven Point Seven Five Twenty Twenty Second Lien Notes [Member] | ||
| Fair Value, Assets And Liabilities Components [Line Items] | ||
| Debt Instrument, Fair Value Disclosure |
$ 397,200,000us-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 |
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- Definition
Debt discount No definition available.
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- Definition
Debt Instrument, Par Value No definition available.
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- Definition
Management Estimate of 62% Fe No definition available.
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- Definition
Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Contractual interest rate for funds borrowed, under the debt agreement. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
The amount of debt discount that was originally recognized at the issuance of the instrument that has yet to be amortized. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
This item represents an other than temporary decline in value that has been recognized against an investment accounted for under the equity method of accounting. The excess of the carrying amount over the fair value of the investment represents the amount of the write down which is or was reflected in earnings. The written down value is a new cost basis with the adjusted value of the investment becoming its new carrying value subject to the equity accounting method. Evidence of a loss in value might include, but would not necessarily be limited to, absence of an ability to recover the carrying amount of the investment or inability of the investee to sustain an earnings capacity which would justify the carrying amount of the investment. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Fair value portion of investments accounted under the equity method. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
The charge against earnings resulting from the write down of long lived assets other than goodwill due to the difference between the carrying value and lower fair value. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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