| DEBT AND CREDIT FACILITIES (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| Mar. 31, 2015 | Mar. 30, 2015 | Dec. 31, 2014 | |||||||
| Line of Credit Facility [Line Items] | |||||||||
| Letters of credit outstanding | $ 136.2us-gaap_LettersOfCreditOutstandingAmount | $ 149.5us-gaap_LettersOfCreditOutstandingAmount | |||||||
| Five hundred forty million Eight point two five Twenty twenty First Lien Notes [Member] | |||||||||
| Line of Credit Facility [Line Items] | |||||||||
| Stated interest rate | 8.25%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = clf_FivehundredfortymillionEightpointtwofiveTwentytwentyFirstLienNotesMember | ||||||||
| Repurchase Price of $540M 8.25% Notes if Triggering Event Occurs | 1.01clf_RepurchasePriceof540M8.25NotesifTriggeringEventOccurs / us-gaap_DebtInstrumentAxis = clf_FivehundredfortymillionEightpointtwofiveTwentytwentyFirstLienNotesMember | ||||||||
| Initial Redemption Price | 1.0825clf_InitialRedemptionPrice / us-gaap_DebtInstrumentAxis = clf_FivehundredfortymillionEightpointtwofiveTwentytwentyFirstLienNotesMember | ||||||||
| Redemption Price after 2018 | 1clf_RedemptionPriceafter2018 / us-gaap_DebtInstrumentAxis = clf_FivehundredfortymillionEightpointtwofiveTwentytwentyFirstLienNotesMember | ||||||||
| Redemption Price from time to time and Prior to March 31, 2018 | 1clf_RedemptionPricefromtimetotimeandPriortoMarch312018 / us-gaap_DebtInstrumentAxis = clf_FivehundredfortymillionEightpointtwofiveTwentytwentyFirstLienNotesMember | ||||||||
| Amount in aggregate that can be redeemed on or prior to March 31, 2018 | 0.35clf_AmountinaggregatethatcanberedeemedonorpriortoMarch312018 / us-gaap_DebtInstrumentAxis = clf_FivehundredfortymillionEightpointtwofiveTwentytwentyFirstLienNotesMember | ||||||||
| Redemption Price of 35 percent or less of Outstanding | 1.0825clf_RedemptionPriceof35percentorlessofOutstanding / us-gaap_DebtInstrumentAxis = clf_FivehundredfortymillionEightpointtwofiveTwentytwentyFirstLienNotesMember | ||||||||
| Amount to Remain Outstanding Prior to March 31, 2018 | 0.65clf_AmounttoRemainOutstandingPriortoMarch312018 / us-gaap_DebtInstrumentAxis = clf_FivehundredfortymillionEightpointtwofiveTwentytwentyFirstLienNotesMember | ||||||||
| In the Event of Default Amount that will Accelerate | 0.25clf_IntheEventofDefaultAmountthatwillAccelerate / us-gaap_DebtInstrumentAxis = clf_FivehundredfortymillionEightpointtwofiveTwentytwentyFirstLienNotesMember | ||||||||
| Debt Instrument, Par Value | 540.0clf_DebtInstrumentParValue / us-gaap_DebtInstrumentAxis = clf_FivehundredfortymillionEightpointtwofiveTwentytwentyFirstLienNotesMember | ||||||||
| Five hundred Forty-four Million Seven Point Seven Five Twenty Twenty Second Lien Notes [Member] | |||||||||
| Line of Credit Facility [Line Items] | |||||||||
| Stated interest rate | 7.75%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = clf_FivehundredFortyfourMillionSevenPointSevenFiveTwentyTwentySecondLienNotesMember | ||||||||
| Initial Redemption Price | 1.03875clf_InitialRedemptionPrice / us-gaap_DebtInstrumentAxis = clf_FivehundredFortyfourMillionSevenPointSevenFiveTwentyTwentySecondLienNotesMember | ||||||||
| Redemption Price beginning March 31, 2019 | 1clf_RedemptionPricebeginningMarch312019 / us-gaap_DebtInstrumentAxis = clf_FivehundredFortyfourMillionSevenPointSevenFiveTwentyTwentySecondLienNotesMember | ||||||||
| Redemption Price from time to time and Prior to March 31, 2017 | 1clf_RedemptionPricefromtimetotimeandPriortoMarch312017 / us-gaap_DebtInstrumentAxis = clf_FivehundredFortyfourMillionSevenPointSevenFiveTwentyTwentySecondLienNotesMember | ||||||||
| Amount in aggregate that can be redeemed on or prior to March 31, 2017 | 0.35clf_AmountinaggregatethatcanberedeemedonorpriortoMarch312017 / us-gaap_DebtInstrumentAxis = clf_FivehundredFortyfourMillionSevenPointSevenFiveTwentyTwentySecondLienNotesMember | ||||||||
| Redemption Price of 35 percent or less of Outstanding | 1.0775clf_RedemptionPriceof35percentorlessofOutstanding / us-gaap_DebtInstrumentAxis = clf_FivehundredFortyfourMillionSevenPointSevenFiveTwentyTwentySecondLienNotesMember | ||||||||
| Amount to Remain Outstanding Prior to March 31, 2018 | 0.65clf_AmounttoRemainOutstandingPriortoMarch312018 / us-gaap_DebtInstrumentAxis = clf_FivehundredFortyfourMillionSevenPointSevenFiveTwentyTwentySecondLienNotesMember | ||||||||
| Debt Instrument, Par Value | 544.2clf_DebtInstrumentParValue / us-gaap_DebtInstrumentAxis = clf_FivehundredFortyfourMillionSevenPointSevenFiveTwentyTwentySecondLienNotesMember | ||||||||
| Revolving Credit Facility [Member] | |||||||||
| Line of Credit Facility [Line Items] | |||||||||
| Revolving credit facility, borrowing capacity | 441.1us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity / us-gaap_DebtInstrumentAxis = us-gaap_RevolvingCreditFacilityMember | ||||||||
| Credit facility, amount outstanding | 0us-gaap_LineOfCredit / us-gaap_DebtInstrumentAxis = us-gaap_RevolvingCreditFacilityMember | [1] | 0us-gaap_LineOfCredit / us-gaap_DebtInstrumentAxis = us-gaap_RevolvingCreditFacilityMember | [2] | |||||
| Debt Instrument, Par Value | 550.0clf_DebtInstrumentParValue / us-gaap_DebtInstrumentAxis = us-gaap_RevolvingCreditFacilityMember | 900.0clf_DebtInstrumentParValue / us-gaap_DebtInstrumentAxis = us-gaap_RevolvingCreditFacilityMember | 1,125.0clf_DebtInstrumentParValue / us-gaap_DebtInstrumentAxis = us-gaap_RevolvingCreditFacilityMember | ||||||
| U.S. Tranche | 450.0clf_U.S.Tranche / us-gaap_DebtInstrumentAxis = us-gaap_RevolvingCreditFacilityMember | ||||||||
| Sublimit for Issuers of Letters of Credit for U.S. Tranche | 250.0clf_SublimitforIssuersofLettersofCreditforU.S.Tranche / us-gaap_DebtInstrumentAxis = us-gaap_RevolvingCreditFacilityMember | ||||||||
| Sublimit for U.S. Swingline Loans | 100.0clf_SublimitforU.S.SwinglineLoans / us-gaap_DebtInstrumentAxis = us-gaap_RevolvingCreditFacilityMember | ||||||||
| Australian Tranche | 100.0clf_AustralianTranche / us-gaap_DebtInstrumentAxis = us-gaap_RevolvingCreditFacilityMember | ||||||||
| Sublimit for Issuance of Letters of Credit for Australian Tranche | 50.0clf_SublimitforIssuanceofLettersofCreditforAustralianTranche / us-gaap_DebtInstrumentAxis = us-gaap_RevolvingCreditFacilityMember | ||||||||
| Sublimit for Australian Swingline Loans | 20.0clf_SublimitforAustralianSwinglineLoans / us-gaap_DebtInstrumentAxis = us-gaap_RevolvingCreditFacilityMember | ||||||||
| Credit facility remaining capacity | 299.4us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity / us-gaap_DebtInstrumentAxis = us-gaap_RevolvingCreditFacilityMember | 975.5us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity / us-gaap_DebtInstrumentAxis = us-gaap_RevolvingCreditFacilityMember | |||||||
| LIBOR Rate Based on a One-month interest period plus 1 percent | 0.01clf_LIBORRateBasedonaOnemonthinterestperiodplus1percent / us-gaap_DebtInstrumentAxis = us-gaap_RevolvingCreditFacilityMember | ||||||||
| Fixed Charge Coverage Ratio | 1.0clf_FixedChargeCoverageRatio / us-gaap_DebtInstrumentAxis = us-gaap_RevolvingCreditFacilityMember | ||||||||
| Letters of credit outstanding | 136.2us-gaap_LettersOfCreditOutstandingAmount / us-gaap_DebtInstrumentAxis = us-gaap_RevolvingCreditFacilityMember | 149.5us-gaap_LettersOfCreditOutstandingAmount / us-gaap_DebtInstrumentAxis = us-gaap_RevolvingCreditFacilityMember | |||||||
| Foreign Exchange Hedge Obligations | $ 5.5clf_ForeignExchangeHedgeObligations / us-gaap_DebtInstrumentAxis = us-gaap_RevolvingCreditFacilityMember | ||||||||
| Revolving Credit Facility [Member] | Minimum [Member] | |||||||||
| Line of Credit Facility [Line Items] | |||||||||
| Base Rate | 0.005clf_BaseRate / us-gaap_DebtInstrumentAxis = us-gaap_RevolvingCreditFacilityMember / us-gaap_RangeAxis = us-gaap_MinimumMember | ||||||||
| Revolving Credit Facility [Member] | Maximum [Member] | |||||||||
| Line of Credit Facility [Line Items] | |||||||||
| Base Rate | 0.01clf_BaseRate / us-gaap_DebtInstrumentAxis = us-gaap_RevolvingCreditFacilityMember / us-gaap_RangeAxis = us-gaap_MaximumMember | ||||||||
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- Definition Amount in aggregate that can be redeemed on or prior to March 31, 2017 No definition available. 
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| X | ||||||||||
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- Definition Amount in aggregate that can be redeemed on or prior to March 31, 2018 No definition available. 
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| X | ||||||||||
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- Definition Amount to Remain Outstanding Prior to March 31, 2018 No definition available. 
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- Definition Australian Tranche No definition available. 
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- Definition Base Rate No definition available. 
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- Definition Debt Instrument, Par Value No definition available. 
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- Definition Fixed Charge Coverage Ratio No definition available. 
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| X | ||||||||||
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- Definition Foreign Exchange Hedge Obligations No definition available. 
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| X | ||||||||||
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- Definition Initial Redemption Price No definition available. 
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- Definition In the Event of Default Amount that will Accelerate No definition available. 
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- Definition LIBOR Rate Based on a One-month interest period plus 1 percent No definition available. 
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- Definition Redemption Price after 2018 No definition available. 
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- Definition Redemption Price beginning March 31, 2019 No definition available. 
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- Definition Redemption Price from time to time and Prior to March 31, 2017 No definition available. 
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- Definition Redemption Price from time to time and Prior to March 31, 2018 No definition available. 
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| X | ||||||||||
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- Definition Redemption Price of 35 percent or less of Outstanding No definition available. 
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| X | ||||||||||
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- Definition Repurchase of $540M 8.25% Notes if Triggering Event Occurs No definition available. 
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| X | ||||||||||
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- Definition Sublimit for Australian Swingline Loans No definition available. 
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| X | ||||||||||
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- Definition Sublimit for Issuance of Letters of Credit for Australian Tranche No definition available. 
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- Definition Sublimit for Issuers of Letters of Credit for U.S. Tranche No definition available. 
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| X | ||||||||||
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- Definition Sublimit for U.S. Swingline Loans No definition available. 
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| X | ||||||||||
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- Definition U.S. Tranche No definition available. 
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| X | ||||||||||
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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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| X | ||||||||||
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- Definition The total amount of the contingent obligation under letters of credit outstanding as of the reporting date. No definition available. 
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| X | ||||||||||
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- Definition The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding). Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Details 
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- Details 
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