Annual report pursuant to Section 13 and 15(d)

QUARTERLY RESULTS OF OPERATIONS (UNAUDITED) QUARTERLY RESULTS OF OPERATIONS (Details)

v2.4.1.9
QUARTERLY RESULTS OF OPERATIONS (UNAUDITED) QUARTERLY RESULTS OF OPERATIONS (Details) (USD $)
Share data in Millions, except Per Share data, unless otherwise specified
 3 Months Ended 12 Months Ended
Dec. 31, 2014
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2013
Sep. 30, 2013
Jun. 30, 2013
Mar. 31, 2013
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Income (Loss) from Continuing Operations Attributable to Parent $ (1,285,100,000)us-gaap_IncomeLossFromContinuingOperations $ (5,879,600,000)us-gaap_IncomeLossFromContinuingOperations $ 10,900,000us-gaap_IncomeLossFromContinuingOperations $ (70,300,000)us-gaap_IncomeLossFromContinuingOperations $ 43,300,000us-gaap_IncomeLossFromContinuingOperations $ 115,200,000us-gaap_IncomeLossFromContinuingOperations $ 146,000,000us-gaap_IncomeLossFromContinuingOperations $ 107,000,000us-gaap_IncomeLossFromContinuingOperations $ (7,224,200,000)us-gaap_IncomeLossFromContinuingOperations $ 411,500,000us-gaap_IncomeLossFromContinuingOperations $ (935,300,000)us-gaap_IncomeLossFromContinuingOperations  
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount 25.2us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount             12.9us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount 25.2us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount      
Goodwill, Impairment Loss                 73,500,000us-gaap_GoodwillImpairmentLoss 80,900,000us-gaap_GoodwillImpairmentLoss    
Loss on sale of Cliffs Logan County Coal                 419,600,000clf_LossonsaleofCliffsLoganCountyCoal 0clf_LossonsaleofCliffsLoganCountyCoal 0clf_LossonsaleofCliffsLoganCountyCoal  
Sale Price of CLCC Assets                 174,000,000clf_SalePriceofCLCCAssets      
Proceeds from sale of Cliffs Logan County Coal                 155,000,000clf_ProceedsfromsaleofCliffsLoganCountyCoal 0clf_ProceedsfromsaleofCliffsLoganCountyCoal 0clf_ProceedsfromsaleofCliffsLoganCountyCoal  
Income Tax Expense (Benefit) (289,700,000)us-gaap_IncomeTaxExpenseBenefit               (1,302,000,000)us-gaap_IncomeTaxExpenseBenefit 55,100,000us-gaap_IncomeTaxExpenseBenefit 255,900,000us-gaap_IncomeTaxExpenseBenefit  
Asset Impairment Charges                 9,029,900,000.0us-gaap_AssetImpairmentCharges 250,800,000.0us-gaap_AssetImpairmentCharges 1,049,900,000.0us-gaap_AssetImpairmentCharges  
Cliffs Chromite Ontario and Cliffs Chromite Far North [Member]                        
Goodwill, Impairment Loss                   80,900,000us-gaap_GoodwillImpairmentLoss
/ clf_ReportingUnitAxis
= clf_CliffsChromiteOntarioandCliffsChromiteFarNorthMember 		   
Wabush [Member]                        
Asset Impairment Charges                 154,600,000.0us-gaap_AssetImpairmentCharges
/ clf_ReportingUnitAxis
= clf_WabushMember 		     
Bloom Lake [Member]                        
Immaterial Error Adjustment Related to Bloom Lake Purchase Price Acquisition                   45,100,000clf_ImmaterialErrorAdjustmentRelatedtoBloomLakePurchasePriceAcquisition
/ clf_NameofOperationAxis
= clf_BloomLakeMember 		   
Change in Basic EPS for Immaterial Error Adjustment Related to Bloom Lake Purchase Price Acquisition         $ 0.29clf_ChangeinBasicEPSforImmaterialErrorAdjustmentRelatedtoBloomLakePurchasePriceAcquisition
/ clf_NameofOperationAxis
= clf_BloomLakeMember 		        $ 0.30clf_ChangeinBasicEPSforImmaterialErrorAdjustmentRelatedtoBloomLakePurchasePriceAcquisition
/ clf_NameofOperationAxis
= clf_BloomLakeMember 		$ 0clf_ChangeinBasicEPSforImmaterialErrorAdjustmentRelatedtoBloomLakePurchasePriceAcquisition
/ clf_NameofOperationAxis
= clf_BloomLakeMember 		$ 0.07clf_ChangeinBasicEPSforImmaterialErrorAdjustmentRelatedtoBloomLakePurchasePriceAcquisition
/ clf_NameofOperationAxis
= clf_BloomLakeMember
Change in Diluted EPS for Immaterial Error Adjustment Related to Bloom Lake Purchase Price Acquisition                   $ 0.26clf_ChangeinDilutedEPSforImmaterialErrorAdjustmentRelatedtoBloomLakePurchasePriceAcquisition
/ clf_NameofOperationAxis
= clf_BloomLakeMember 		$ 0.25clf_ChangeinDilutedEPSforImmaterialErrorAdjustmentRelatedtoBloomLakePurchasePriceAcquisition
/ clf_NameofOperationAxis
= clf_BloomLakeMember 		$ 0.07clf_ChangeinDilutedEPSforImmaterialErrorAdjustmentRelatedtoBloomLakePurchasePriceAcquisition
/ clf_NameofOperationAxis
= clf_BloomLakeMember
Minimum [Member]                        
Income (Loss) from Continuing Operations Attributable to Parent                 300,000us-gaap_IncomeLossFromContinuingOperations
/ us-gaap_RangeAxis
= us-gaap_MinimumMember 		     
Maximum [Member]                        
Income (Loss) from Continuing Operations Attributable to Parent                 800,000us-gaap_IncomeLossFromContinuingOperations
/ us-gaap_RangeAxis
= us-gaap_MaximumMember 		     
Bloom Lake [Member]                        
Asset Impairment Charges                 $ 1,300,000,000.0us-gaap_AssetImpairmentCharges
/ clf_AssetgroupAxis
= clf_BloomLakeMember