Quarterly report pursuant to Section 13 or 15(d)

SHAREHOLDERS' EQUITY Schedule of Shareholders' Equity (Details)

v2.4.1.9
SHAREHOLDERS' EQUITY Schedule of Shareholders' Equity (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Dec. 31, 2013
Stockholders' Equity Attributable to Parent $ (1,995.7)us-gaap_StockholdersEquity   $ (1,431.3)us-gaap_StockholdersEquity  
Stockholders' Equity Attributable to Noncontrolling Interest 213.6us-gaap_MinorityInterest   (303.0)us-gaap_MinorityInterest  
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest (1,782.1)us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest 6,835.6us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest (1,734.3)us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest 6,884.3us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest
NET LOSS ATTRIBUTABLE TO CLIFFS SHAREHOLDERS (759.8)us-gaap_NetIncomeLoss (70.3)us-gaap_NetIncomeLoss    
INCOME (LOSS) ATTRIBUTABLE TO NONCONTROLLING INTEREST (1.9)us-gaap_NetIncomeLossAttributableToNoncontrollingInterest (0.4)us-gaap_NetIncomeLossAttributableToNoncontrollingInterest    
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest (761.7)us-gaap_ProfitLoss (70.7)us-gaap_ProfitLoss    
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent (552.2)us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent (12.5)us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent    
Other Comprehensive Income (Loss), Net of Tax 196.8us-gaap_OtherComprehensiveIncomeLossNetOfTax 58.3us-gaap_OtherComprehensiveIncomeLossNetOfTax    
OTHER COMPREHENSIVE LOSS (INCOME) ATTRIBUTABLE TO THE NONCONTROLLING INTEREST 10.8us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest (0.5)us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest    
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest (564.9)us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest (12.4)us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest    
Deconsolidation, Gain (Loss), Amount 528.2us-gaap_DeconsolidationGainOrLossAmount      
Stock and Other Incentive Plans 0.6us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue (1.4)us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue    
Preferred share dividends (12.8)us-gaap_DividendsStock (36.1)us-gaap_DividendsStock    
Undistributed Gains To Noncontrolling Interest 1.1clf_UndistributedEarningsLossesRelatedToNoncontrollingInterests 1.2clf_UndistributedEarningsLossesRelatedToNoncontrollingInterests    
Cliffs Shareholders Equity [Member]        
Stockholders' Equity Attributable to Parent (1,995.7)us-gaap_StockholdersEquity
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_ParentMember
6,019.5us-gaap_StockholdersEquity
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_ParentMember
(1,431.3)us-gaap_StockholdersEquity
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_ParentMember
6,069.5us-gaap_StockholdersEquity
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_ParentMember
NET LOSS ATTRIBUTABLE TO CLIFFS SHAREHOLDERS (759.8)us-gaap_NetIncomeLoss
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_ParentMember
(70.3)us-gaap_NetIncomeLoss
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_ParentMember
   
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent 207.6us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_ParentMember
57.8us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_ParentMember
   
Comprehensive Income (Loss), Net of Tax, Attributable to Parent (552.2)us-gaap_ComprehensiveIncomeNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_ParentMember
(12.5)us-gaap_ComprehensiveIncomeNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_ParentMember
   
Deconsolidation, Gain (Loss), Amount 0us-gaap_DeconsolidationGainOrLossAmount
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_ParentMember
     
Stock and Other Incentive Plans 0.6us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_ParentMember
(1.4)us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_ParentMember
   
Preferred share dividends (12.8)us-gaap_DividendsStock
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_ParentMember
(36.1)us-gaap_DividendsStock
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_ParentMember
   
Undistributed Gains To Noncontrolling Interest 0clf_UndistributedEarningsLossesRelatedToNoncontrollingInterests
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_ParentMember
0clf_UndistributedEarningsLossesRelatedToNoncontrollingInterests
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_ParentMember
   
Noncontrolling Interest [Member]        
Stockholders' Equity Attributable to Noncontrolling Interest 213.6us-gaap_MinorityInterest
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember
816.1us-gaap_MinorityInterest
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember
(303.0)us-gaap_MinorityInterest
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember
814.8us-gaap_MinorityInterest
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember
INCOME (LOSS) ATTRIBUTABLE TO NONCONTROLLING INTEREST (1.9)us-gaap_NetIncomeLossAttributableToNoncontrollingInterest
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember
(0.4)us-gaap_NetIncomeLossAttributableToNoncontrollingInterest
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember
   
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest (10.8)us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember
0.5us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember
   
OTHER COMPREHENSIVE LOSS (INCOME) ATTRIBUTABLE TO THE NONCONTROLLING INTEREST (12.7)us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember
0.1us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember
   
Deconsolidation, Gain (Loss), Amount 528.2us-gaap_DeconsolidationGainOrLossAmount
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember
     
Stock and Other Incentive Plans 0us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember
0us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember
   
Preferred share dividends 0us-gaap_DividendsStock
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember
0us-gaap_DividendsStock
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember
   
Undistributed Gains To Noncontrolling Interest $ 1.1clf_UndistributedEarningsLossesRelatedToNoncontrollingInterests
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember
$ 1.2clf_UndistributedEarningsLossesRelatedToNoncontrollingInterests
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember