Annual report pursuant to Section 13 and 15(d)

SUBSEQUENT EVENTS Narrative (Details)

v2.4.1.9
SUBSEQUENT EVENTS Narrative (Details) (USD $)
12 Months Ended 11 Months Ended
Dec. 31, 2014
Dec. 31, 2015
Dec. 31, 2013
Jan. 26, 2015
Sep. 30, 2014
May 31, 2015
Jan. 22, 2015
Subsequent Event [Line Items]              
Debt Instrument, Par Value $ 4,144,800,000clf_DebtInstrumentParValue   $ 4,814,800,000clf_DebtInstrumentParValue        
Estimated Capital Costs to Develop Bloom Lake Phase II 1,200,000,000clf_EstimatedCapitalCoststoDevelopBloomLakePhaseII            
Elimination of Dividend [Member]              
Subsequent Event [Line Items]              
Elimination of Dividend       $ 0.15clf_EliminationofDividend
/ us-gaap_SubsequentEventTypeAxis
= clf_EliminationofDividendMember
     
Free Cash Flow Due to Quarterly Dividend Elimination       92,000,000clf_FreeCashFlowDuetoQuarterlyDividendElimination
/ us-gaap_SubsequentEventTypeAxis
= clf_EliminationofDividendMember
     
Revolving Credit Facility [Member]              
Subsequent Event [Line Items]              
Debt Instrument, Par Value 1,125,000,000clf_DebtInstrumentParValue
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember
  1,750,000,000clf_DebtInstrumentParValue
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember
  1,250,000,000clf_DebtInstrumentParValue
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember
   
Revolving Credit Facility [Member] | Revolving Credit Facility [Member]              
Subsequent Event [Line Items]              
Debt Instrument, Face Amount, Subsequent Event - Revolving Credit Facility Amendment           750,000,000clf_DebtInstrumentFaceAmountSubsequentEventRevolvingCreditFacilityAmendment
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_RevolvingCreditFacilityMember
900,000,000clf_DebtInstrumentFaceAmountSubsequentEventRevolvingCreditFacilityAmendment
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_RevolvingCreditFacilityMember
Permit Costs and Expenses in connection with Canadian Restructuring EBITDA Add back- Subsequent Event - Revolving Credit Facility Amendment   $ 75,000,000clf_PermitCostsandExpensesinconnectionwithCanadianRestructuringEBITDAAddbackSubsequentEventRevolvingCreditFacilityAmendment
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_RevolvingCreditFacilityMember
         
Limit on Dividend per Share - Subsequent Event - Revolving Credit Facility Amendment   $ 0.01clf_LimitonDividendperShareSubsequentEventRevolvingCreditFacilityAmendment
/ us-gaap_DebtInstrumentAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_RevolvingCreditFacilityMember