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Annual report pursuant to Section 13 and 15(d)

SEGMENT REPORTING (Schedule Of Segment Reporting Information, By Segment) (Details)

v2.4.1.9
SEGMENT REPORTING (Schedule Of Segment Reporting Information, By Segment) (Details) (USD $)
In Millions, 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
Segment Reporting Information [Line Items] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Net income (loss) Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý $ (8,311.6)us-gaap_ProfitLoss $ 361.8us-gaap_ProfitLoss $ (1,126.6)us-gaap_ProfitLoss
Revenues from product sales and services 1,284.7us-gaap_Revenues 1,298.2us-gaap_Revenues 1,100.8us-gaap_Revenues 940.0us-gaap_Revenues 1,515.8us-gaap_Revenues 1,546.6us-gaap_Revenues 1,488.5us-gaap_Revenues 1,140.5us-gaap_Revenues 4,623.7us-gaap_Revenues 5,691.4us-gaap_Revenues 5,872.7us-gaap_Revenues
Revenues from producet sales and services, percent Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 100.00%clf_PercentageOfSegmentRevenue 100.00%clf_PercentageOfSegmentRevenue 100.00%clf_PercentageOfSegmentRevenue
SALES MARGIN 168.7us-gaap_GrossProfit 127.5us-gaap_GrossProfit 92.0us-gaap_GrossProfit 63.2us-gaap_GrossProfit 294.5us-gaap_GrossProfit 348.7us-gaap_GrossProfit 268.2us-gaap_GrossProfit 237.9us-gaap_GrossProfit 451.4us-gaap_GrossProfit 1,149.3us-gaap_GrossProfit 1,172.1us-gaap_GrossProfit
Other operating expense Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý (9,896.7)us-gaap_OperatingExpenses (478.3)us-gaap_OperatingExpenses (1,480.9)us-gaap_OperatingExpenses
Other expense Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý (158.4)us-gaap_NonoperatingIncomeExpense (181.7)us-gaap_NonoperatingIncomeExpense (193.0)us-gaap_NonoperatingIncomeExpense
Income (loss) from continuing operations before income taxes and equity income (loss) from ventures Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý (9,603.7)us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments 489.3us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments (501.8)us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments
Depreciation, depletion and amortization Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 504.0us-gaap_DepreciationDepletionAndAmortization 593.3us-gaap_DepreciationDepletionAndAmortization 525.8us-gaap_DepreciationDepletionAndAmortization
Capital Additions Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 235.5us-gaap_PropertyPlantAndEquipmentAdditions 752.3us-gaap_PropertyPlantAndEquipmentAdditions 1,335.3us-gaap_PropertyPlantAndEquipmentAdditions
Interest expense, net Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý (185.2)us-gaap_InterestIncomeExpenseNet (179.1)us-gaap_InterestIncomeExpenseNet (195.6)us-gaap_InterestIncomeExpenseNet
Income Tax Expense (Benefit) (289.7)us-gaap_IncomeTaxExpenseBenefit Ìý Ìý Ìý Ìý Ìý Ìý Ìý (1,302.0)us-gaap_IncomeTaxExpenseBenefit 55.1us-gaap_IncomeTaxExpenseBenefit 255.9us-gaap_IncomeTaxExpenseBenefit
EBITDA Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý (8,924.4)clf_EBITDA 1,189.3clf_EBITDA (149.3)clf_EBITDA
Equity Method Investment, Other than Temporary Impairment Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 0us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment 0us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment (365.4)us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment
Loss on sale of Cliffs Logan County Coal Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 419.6clf_LossonsaleofCliffsLoganCountyCoal 0clf_LossonsaleofCliffsLoganCountyCoal 0clf_LossonsaleofCliffsLoganCountyCoal
Adjusted EBITDA Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 929.7clf_AdjustedEBITDA 1,428.3clf_AdjustedEBITDA 1,292.9clf_AdjustedEBITDA
U.S. Iron Ore [Member] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Segment Reporting Information [Line Items] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Revenues from product sales and services Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 2,506.5us-gaap_Revenues
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember 		2,667.9us-gaap_Revenues
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember 		2,723.3us-gaap_Revenues
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
Revenues from producet sales and services, percent Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 54.00%clf_PercentageOfSegmentRevenue
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember 		47.00%clf_PercentageOfSegmentRevenue
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember 		46.00%clf_PercentageOfSegmentRevenue
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
SALES MARGIN Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 710.4us-gaap_GrossProfit
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember 		901.9us-gaap_GrossProfit
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember 		976.2us-gaap_GrossProfit
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
Depreciation, depletion and amortization Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 107.4us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember 		120.3us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember 		100.9us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
Capital Additions Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 48.4us-gaap_PropertyPlantAndEquipmentAdditions
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember 		[1] 53.3us-gaap_PropertyPlantAndEquipmentAdditions
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember 		[1] 168.8us-gaap_PropertyPlantAndEquipmentAdditions
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember 		[1]
EBITDA Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 805.6clf_EBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember 		1,000.1clf_EBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember 		1,045.3clf_EBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
Adjusted EBITDA Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 831.2clf_AdjustedEBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember 		1,030.8clf_AdjustedEBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember 		1,085.6clf_AdjustedEBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
Eastern Canadian Iron Ore [Member] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Segment Reporting Information [Line Items] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Revenues from product sales and services Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 563.4us-gaap_Revenues
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember 		978.7us-gaap_Revenues
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember 		1,008.9us-gaap_Revenues
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember
Revenues from producet sales and services, percent Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 12.00%clf_PercentageOfSegmentRevenue
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember 		17.00%clf_PercentageOfSegmentRevenue
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember 		17.00%clf_PercentageOfSegmentRevenue
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember
SALES MARGIN Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý (244.9)us-gaap_GrossProfit
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember 		(103.3)us-gaap_GrossProfit
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember 		(121.4)us-gaap_GrossProfit
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember
Depreciation, depletion and amortization Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 135.6us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember 		178.5us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember 		160.2us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember
Capital Additions Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 141.2us-gaap_PropertyPlantAndEquipmentAdditions
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember 		[1] 625.5us-gaap_PropertyPlantAndEquipmentAdditions
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember 		[1] 865.2us-gaap_PropertyPlantAndEquipmentAdditions
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember 		[1]
EBITDA Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý (7,673.9)clf_EBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember 		(192.8)clf_EBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember 		(1,103.3)clf_EBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember
Adjusted EBITDA Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 0clf_AdjustedEBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember 		0clf_AdjustedEBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember 		0clf_AdjustedEBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember
Asia Pacific Iron Ore [Member] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Segment Reporting Information [Line Items] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Revenues from product sales and services Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 866.7us-gaap_Revenues
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember 		1,224.3us-gaap_Revenues
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember 		1,259.3us-gaap_Revenues
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
Revenues from producet sales and services, percent Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 19.00%clf_PercentageOfSegmentRevenue
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember 		22.00%clf_PercentageOfSegmentRevenue
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember 		22.00%clf_PercentageOfSegmentRevenue
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
SALES MARGIN Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 121.7us-gaap_GrossProfit
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember 		367.1us-gaap_GrossProfit
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember 		311.0us-gaap_GrossProfit
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
Depreciation, depletion and amortization Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 145.9us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember 		153.7us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember 		151.9us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
Capital Additions Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 10.8us-gaap_PropertyPlantAndEquipmentAdditions
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember 		[1] 13.0us-gaap_PropertyPlantAndEquipmentAdditions
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember 		[1] 87.7us-gaap_PropertyPlantAndEquipmentAdditions
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember 		[1]
EBITDA Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý (369.8)clf_EBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember 		500.4clf_EBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember 		387.3clf_EBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
Adjusted EBITDA Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 264.6clf_AdjustedEBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember 		525.7clf_AdjustedEBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember 		402.1clf_AdjustedEBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
North American Coal [Member] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Segment Reporting Information [Line Items] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Revenues from product sales and services Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 687.1us-gaap_Revenues
/ us-gaap_StatementBusinessSegmentsAxis
= clf_NorthAmericanCoalMember 		821.9us-gaap_Revenues
/ us-gaap_StatementBusinessSegmentsAxis
= clf_NorthAmericanCoalMember 		881.1us-gaap_Revenues
/ us-gaap_StatementBusinessSegmentsAxis
= clf_NorthAmericanCoalMember
Revenues from producet sales and services, percent Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 15.00%clf_PercentageOfSegmentRevenue
/ us-gaap_StatementBusinessSegmentsAxis
= clf_NorthAmericanCoalMember 		14.00%clf_PercentageOfSegmentRevenue
/ us-gaap_StatementBusinessSegmentsAxis
= clf_NorthAmericanCoalMember 		15.00%clf_PercentageOfSegmentRevenue
/ us-gaap_StatementBusinessSegmentsAxis
= clf_NorthAmericanCoalMember
SALES MARGIN Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý (135.8)us-gaap_GrossProfit
/ us-gaap_StatementBusinessSegmentsAxis
= clf_NorthAmericanCoalMember 		(14.5)us-gaap_GrossProfit
/ us-gaap_StatementBusinessSegmentsAxis
= clf_NorthAmericanCoalMember 		(1.8)us-gaap_GrossProfit
/ us-gaap_StatementBusinessSegmentsAxis
= clf_NorthAmericanCoalMember
Depreciation, depletion and amortization Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 106.9us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= clf_NorthAmericanCoalMember 		128.9us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= clf_NorthAmericanCoalMember 		98.2us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= clf_NorthAmericanCoalMember
Capital Additions Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 28.8us-gaap_PropertyPlantAndEquipmentAdditions
/ us-gaap_StatementBusinessSegmentsAxis
= clf_NorthAmericanCoalMember 		[1] 55.0us-gaap_PropertyPlantAndEquipmentAdditions
/ us-gaap_StatementBusinessSegmentsAxis
= clf_NorthAmericanCoalMember 		[1] 144.1us-gaap_PropertyPlantAndEquipmentAdditions
/ us-gaap_StatementBusinessSegmentsAxis
= clf_NorthAmericanCoalMember 		[1]
EBITDA Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý (1,326.8)clf_EBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_NorthAmericanCoalMember 		129.5clf_EBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_NorthAmericanCoalMember 		74.0clf_EBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_NorthAmericanCoalMember
Adjusted EBITDA Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý (28.5)clf_AdjustedEBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_NorthAmericanCoalMember 		154.0clf_AdjustedEBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_NorthAmericanCoalMember 		106.7clf_AdjustedEBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_NorthAmericanCoalMember
All Other Segments [Member] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Segment Reporting Information [Line Items] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Revenues from product sales and services Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 0us-gaap_Revenues
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember 		(1.4)us-gaap_Revenues
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember 		0.1us-gaap_Revenues
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember
Revenues from producet sales and services, percent Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 0.00%clf_PercentageOfSegmentRevenue
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember 		0.00%clf_PercentageOfSegmentRevenue
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember 		0.00%clf_PercentageOfSegmentRevenue
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember
SALES MARGIN Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 0us-gaap_GrossProfit
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember 		(1.9)us-gaap_GrossProfit
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember 		8.1us-gaap_GrossProfit
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember
Depreciation, depletion and amortization Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 8.2us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember 		11.9us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember 		14.6us-gaap_DepreciationDepletionAndAmortization
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember
Capital Additions Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 6.3us-gaap_PropertyPlantAndEquipmentAdditions
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember 		[1] 5.5us-gaap_PropertyPlantAndEquipmentAdditions
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember 		[1] 69.5us-gaap_PropertyPlantAndEquipmentAdditions
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_AllOtherSegmentsMember 		[1]
Other Segment [Member] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Segment Reporting Information [Line Items] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
EBITDA Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý (359.5)clf_EBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_OtherSegmentMember 		(247.9)clf_EBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_OtherSegmentMember 		(552.6)clf_EBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_OtherSegmentMember
Adjusted EBITDA Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý (137.6)clf_AdjustedEBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_OtherSegmentMember 		(282.2)clf_AdjustedEBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_OtherSegmentMember 		(301.5)clf_AdjustedEBITDA
/ us-gaap_StatementBusinessSegmentsAxis
= clf_OtherSegmentMember
EBITDA Calculation [Member] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Segment Reporting Information [Line Items] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Depreciation, depletion and amortization Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý (504.0)us-gaap_DepreciationDepletionAndAmortization
/ clf_EBITDACalculationAxis
= clf_EBITDACalculationMember 		(593.3)us-gaap_DepreciationDepletionAndAmortization
/ clf_EBITDACalculationAxis
= clf_EBITDACalculationMember 		(525.8)us-gaap_DepreciationDepletionAndAmortization
/ clf_EBITDACalculationAxis
= clf_EBITDACalculationMember
Amapa [Member] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Segment Reporting Information [Line Items] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Equity Method Investment, Other than Temporary Impairment Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 67.6us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_AmapaMember 		(365.4)us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_AmapaMember
Adjusted EBITDA Calculation [Member] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Segment Reporting Information [Line Items] Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý
Loss on sale of Cliffs Logan County Coal Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý (419.6)clf_LossonsaleofCliffsLoganCountyCoal
/ clf_AdjustedEBITACalculationAxis
= clf_AdjustedEBITDACalculationMember 		0clf_LossonsaleofCliffsLoganCountyCoal
/ clf_AdjustedEBITACalculationAxis
= clf_AdjustedEBITDACalculationMember 		0clf_LossonsaleofCliffsLoganCountyCoal
/ clf_AdjustedEBITACalculationAxis
= clf_AdjustedEBITDACalculationMember
Wabush mine related costs Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý (158.7)clf_Wabushminerelatedcosts
/ clf_AdjustedEBITACalculationAxis
= clf_AdjustedEBITDACalculationMember 		(72.7)clf_Wabushminerelatedcosts
/ clf_AdjustedEBITACalculationAxis
= clf_AdjustedEBITDACalculationMember 		(30.1)clf_Wabushminerelatedcosts
/ clf_AdjustedEBITACalculationAxis
= clf_AdjustedEBITDACalculationMember
Bloom Lake mine costs Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý (137.9)clf_BloomLakeminecosts
/ clf_AdjustedEBITACalculationAxis
= clf_AdjustedEBITDACalculationMember 		46.5clf_BloomLakeminecosts
/ clf_AdjustedEBITACalculationAxis
= clf_AdjustedEBITDACalculationMember 		6.4clf_BloomLakeminecosts
/ clf_AdjustedEBITACalculationAxis
= clf_AdjustedEBITDACalculationMember
Foreign Exchange Remeasurement Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý 30.7clf_ForeignExchangeRemeasurement
/ clf_AdjustedEBITACalculationAxis
= clf_AdjustedEBITDACalculationMember 		64.0clf_ForeignExchangeRemeasurement
/ clf_AdjustedEBITACalculationAxis
= clf_AdjustedEBITDACalculationMember 		(3.2)clf_ForeignExchangeRemeasurement
/ clf_AdjustedEBITACalculationAxis
= clf_AdjustedEBITDACalculationMember
Proxy contest and change in control costs in SG&A Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý (26.6)clf_ProxycontestandchangeincontrolcostsinSGA
/ clf_AdjustedEBITACalculationAxis
= clf_AdjustedEBITDACalculationMember 		0clf_ProxycontestandchangeincontrolcostsinSGA
/ clf_AdjustedEBITACalculationAxis
= clf_AdjustedEBITDACalculationMember 		0clf_ProxycontestandchangeincontrolcostsinSGA
/ clf_AdjustedEBITACalculationAxis
= clf_AdjustedEBITDACalculationMember
Litigation Judgment Costs Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý (96.3)clf_LitigationJudgmentCosts
/ clf_AdjustedEBITACalculationAxis
= clf_AdjustedEBITDACalculationMember 		(9.6)clf_LitigationJudgmentCosts
/ clf_AdjustedEBITACalculationAxis
= clf_AdjustedEBITDACalculationMember 		0clf_LitigationJudgmentCosts
/ clf_AdjustedEBITACalculationAxis
= clf_AdjustedEBITDACalculationMember
Severance Costs in SG&A Ìý Ìý Ìý Ìý Ìý Ìý Ìý Ìý $ (15.8)clf_SeveranceCostsinSGA
/ clf_AdjustedEBITACalculationAxis
= clf_AdjustedEBITDACalculationMember 		$ (16.4)clf_SeveranceCostsinSGA
/ clf_AdjustedEBITACalculationAxis
= clf_AdjustedEBITDACalculationMember 		$ 0clf_SeveranceCostsinSGA
/ clf_AdjustedEBITACalculationAxis
= clf_AdjustedEBITDACalculationMember
[1] 1 Includes capital lease additions and non-cash accruals. Refer to NOTE 17 - CASH FLOW INFORMATION.