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Annual report pursuant to Section 13 and 15(d)

INVENTORIES (Narrative) (Details)

v2.4.1.9
INVENTORIES (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
U.S. Iron Ore [Member] Ìý Ìý Ìý
Inventory [Line Items] Ìý Ìý Ìý
Inventory, LIFO Reserve $ 119.0us-gaap_InventoryLIFOReserve
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember 		$ 115.3us-gaap_InventoryLIFOReserve
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember 		Ìý
Effect of LIFO Inventory Liquidation on Income 44.8us-gaap_EffectOfLIFOInventoryLiquidationOnIncome
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember 		Ìý Ìý
Increase in Inventories due to build up of LIFO layers Ìý 7.4clf_IncreaseInInventoriesDueToBuildUpOfLifoLayers
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember 		Ìý
Cost of Sales [Member] | Eastern Canadian Iron Ore [Member] Ìý Ìý Ìý
Inventory [Line Items] Ìý Ìý Ìý
Inventory Write-down 38.9us-gaap_InventoryWriteDown
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember 		Ìý 0us-gaap_InventoryWriteDown
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember
Cost of Sales [Member] | North American Coal [Member] Ìý Ìý Ìý
Inventory [Line Items] Ìý Ìý Ìý
Inventory Write-down 44.5us-gaap_InventoryWriteDown
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember
/ us-gaap_StatementBusinessSegmentsAxis
= clf_NorthAmericanCoalMember 		11.1us-gaap_InventoryWriteDown
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember
/ us-gaap_StatementBusinessSegmentsAxis
= clf_NorthAmericanCoalMember 		24.4us-gaap_InventoryWriteDown
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember
/ us-gaap_StatementBusinessSegmentsAxis
= clf_NorthAmericanCoalMember
Work in process inventory [Member] | Bloom Lake [Member] | Cost of Sales [Member] Ìý Ìý Ìý
Inventory [Line Items] Ìý Ìý Ìý
Inventory Write-down 0us-gaap_InventoryWriteDown
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember
/ us-gaap_PublicUtilitiesInventoryAxis
= clf_WorkinprocessinventoryMember
/ clf_ReportingUnitAxis
= clf_BloomLakeMember 		Ìý Ìý
Work in process inventory [Member] | Wabush [Member] | Cost of Sales [Member] Ìý Ìý Ìý
Inventory [Line Items] Ìý Ìý Ìý
Inventory Write-down 0us-gaap_InventoryWriteDown
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember
/ us-gaap_PublicUtilitiesInventoryAxis
= clf_WorkinprocessinventoryMember
/ clf_ReportingUnitAxis
= clf_WabushMember 		Ìý Ìý
Finished goods inventory [Member] | Bloom Lake [Member] | Cost of Sales [Member] Ìý Ìý Ìý
Inventory [Line Items] Ìý Ìý Ìý
Inventory Write-down 0us-gaap_InventoryWriteDown
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember
/ us-gaap_PublicUtilitiesInventoryAxis
= clf_FinishedgoodsinventoryMember
/ clf_ReportingUnitAxis
= clf_BloomLakeMember 		Ìý Ìý
Finished goods inventory [Member] | Wabush [Member] | Cost of Sales [Member] Ìý Ìý Ìý
Inventory [Line Items] Ìý Ìý Ìý
Inventory Write-down 0us-gaap_InventoryWriteDown
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember
/ us-gaap_PublicUtilitiesInventoryAxis
= clf_FinishedgoodsinventoryMember
/ clf_ReportingUnitAxis
= clf_WabushMember 		Ìý Ìý
Pellets [Member] | Cost of Sales [Member] | Eastern Canadian Iron Ore [Member] Ìý Ìý Ìý
Inventory [Line Items] Ìý Ìý Ìý
Inventory Write-down Ìý 11.1us-gaap_InventoryWriteDown
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember
/ us-gaap_PublicUtilitiesInventoryAxis
= clf_PelletsMember
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember 		Ìý
Pellets [Member] | Wabush [Member] | Cost of Sales [Member] Ìý Ìý Ìý
Inventory [Line Items] Ìý Ìý Ìý
Unsaleable Inventory Impairment Charge Ìý 10.6clf_UnsaleableInventoryImpairmentCharge
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember
/ us-gaap_PublicUtilitiesInventoryAxis
= clf_PelletsMember
/ clf_ReportingUnitAxis
= clf_WabushMember 		Ìý
Concentrate [Member] | Cost of Sales [Member] | Eastern Canadian Iron Ore [Member] Ìý Ìý Ìý
Inventory [Line Items] Ìý Ìý Ìý
Inventory Write-down Ìý 13.2us-gaap_InventoryWriteDown
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember
/ us-gaap_PublicUtilitiesInventoryAxis
= clf_ConcentrateMember
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember 		Ìý
Concentrate [Member] | Wabush [Member] | Cost of Sales [Member] Ìý Ìý Ìý
Inventory [Line Items] Ìý Ìý Ìý
Unsaleable Inventory Impairment Charge Ìý $ 7.9clf_UnsaleableInventoryImpairmentCharge
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember
/ us-gaap_PublicUtilitiesInventoryAxis
= clf_ConcentrateMember
/ clf_ReportingUnitAxis
= clf_WabushMember 		Ìý