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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 Ìý
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount 25.2us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount Ìý Ìý Ìý Ìý Ìý Ìý 12.9us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount 25.2us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount Ìý Ìý Ìý
Goodwill, Impairment Loss Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 73,500,000us-gaap_GoodwillImpairmentLoss 80,900,000us-gaap_GoodwillImpairmentLoss Ìý Ìý
Loss on sale of Cliffs Logan County Coal Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 419,600,000clf_LossonsaleofCliffsLoganCountyCoal 0clf_LossonsaleofCliffsLoganCountyCoal 0clf_LossonsaleofCliffsLoganCountyCoal Ìý
Sale Price of CLCC Assets Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 174,000,000clf_SalePriceofCLCCAssets Ìý Ìý Ìý
Proceeds from sale of Cliffs Logan County Coal Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 155,000,000clf_ProceedsfromsaleofCliffsLoganCountyCoal 0clf_ProceedsfromsaleofCliffsLoganCountyCoal 0clf_ProceedsfromsaleofCliffsLoganCountyCoal Ìý
Income Tax Expense (Benefit) (289,700,000)us-gaap_IncomeTaxExpenseBenefit Ìý Ìý Ìý Ìý Ìý Ìý Ìý (1,302,000,000)us-gaap_IncomeTaxExpenseBenefit 55,100,000us-gaap_IncomeTaxExpenseBenefit 255,900,000us-gaap_IncomeTaxExpenseBenefit Ìý
Asset Impairment Charges Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 9,029,900,000.0us-gaap_AssetImpairmentCharges 250,800,000.0us-gaap_AssetImpairmentCharges 1,049,900,000.0us-gaap_AssetImpairmentCharges Ìý
Cliffs Chromite Ontario and Cliffs Chromite Far North [Member] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Goodwill, Impairment Loss Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 80,900,000us-gaap_GoodwillImpairmentLoss
/ clf_ReportingUnitAxis
= clf_CliffsChromiteOntarioandCliffsChromiteFarNorthMember 		Ìý Ìý
Wabush [Member] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Asset Impairment Charges Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 154,600,000.0us-gaap_AssetImpairmentCharges
/ clf_ReportingUnitAxis
= clf_WabushMember 		Ìý Ìý Ìý
Bloom Lake [Member] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Immaterial Error Adjustment Related to Bloom Lake Purchase Price Acquisition Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 45,100,000clf_ImmaterialErrorAdjustmentRelatedtoBloomLakePurchasePriceAcquisition
/ clf_NameofOperationAxis
= clf_BloomLakeMember 		Ìý Ìý
Change in Basic EPS for Immaterial Error Adjustment Related to Bloom Lake Purchase Price Acquisition Ìý Ìý Ìý Ìý $ 0.29clf_ChangeinBasicEPSforImmaterialErrorAdjustmentRelatedtoBloomLakePurchasePriceAcquisition
/ clf_NameofOperationAxis
= clf_BloomLakeMember 		Ìý Ìý Ìý Ìý $ 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 Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý $ 0.26clf_ChangeinDilutedEPSforImmaterialErrorAdjustmentRelatedtoBloomLakePurchasePriceAcquisition
/ clf_NameofOperationAxis
= clf_BloomLakeMember 		$ 0.25clf_ChangeinDilutedEPSforImmaterialErrorAdjustmentRelatedtoBloomLakePurchasePriceAcquisition
/ clf_NameofOperationAxis
= clf_BloomLakeMember 		$ 0.07clf_ChangeinDilutedEPSforImmaterialErrorAdjustmentRelatedtoBloomLakePurchasePriceAcquisition
/ clf_NameofOperationAxis
= clf_BloomLakeMember
Minimum [Member] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Income (Loss) from Continuing Operations Attributable to Parent Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 300,000us-gaap_IncomeLossFromContinuingOperations
/ us-gaap_RangeAxis
= us-gaap_MinimumMember 		Ìý Ìý Ìý
Maximum [Member] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Income (Loss) from Continuing Operations Attributable to Parent Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 800,000us-gaap_IncomeLossFromContinuingOperations
/ us-gaap_RangeAxis
= us-gaap_MaximumMember 		Ìý Ìý Ìý
Bloom Lake [Member] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Asset Impairment Charges Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý $ 1,300,000,000.0us-gaap_AssetImpairmentCharges
/ clf_AssetgroupAxis
= clf_BloomLakeMember 		Ìý Ìý Ìý