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Annual report pursuant to Section 13 and 15(d)

GOODWILL AND OTHER INTANGIBLE ASSETS AND LIABILITIES (Narrative) (Details)

v2.4.1.9
GOODWILL AND OTHER INTANGIBLE ASSETS AND LIABILITIES (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Goodwill [Line Items] Ìý Ìý Ìý
Goodwill, Impairment Loss $ 73.5us-gaap_GoodwillImpairmentLoss $ 80.9us-gaap_GoodwillImpairmentLoss Ìý
Product 4,230.8us-gaap_SalesRevenueGoodsNet 5,346.6us-gaap_SalesRevenueGoodsNet 5,520.9us-gaap_SalesRevenueGoodsNet
Below-market sales contracts, remaining contract life 2 years Ìý Ìý
Cost of Sales [Member] Ìý Ìý Ìý
Goodwill [Line Items] Ìý Ìý Ìý
Amortization expense relating to intangible assets 10.4us-gaap_AmortizationOfIntangibleAssets
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember 		19.9us-gaap_AmortizationOfIntangibleAssets
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember 		22.5us-gaap_AmortizationOfIntangibleAssets
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember
Product Revenues [Member] | Sales Revenue, Goods, Net [Member] Ìý Ìý Ìý
Goodwill [Line Items] Ìý Ìý Ìý
Product 23.1us-gaap_SalesRevenueGoodsNet
/ clf_BelowMarketSalesContractsAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesRevenueGoodsNetMember 		45.9us-gaap_SalesRevenueGoodsNet
/ clf_BelowMarketSalesContractsAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesRevenueGoodsNetMember 		46.3us-gaap_SalesRevenueGoodsNet
/ clf_BelowMarketSalesContractsAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesRevenueGoodsNetMember
Cliffs Chromite Ontario and Cliffs Chromite Far North [Member] Ìý Ìý Ìý
Goodwill [Line Items] Ìý Ìý Ìý
Goodwill, Impairment Loss Ìý 80.9us-gaap_GoodwillImpairmentLoss
/ clf_ReportingUnitAxis
= clf_CliffsChromiteOntarioandCliffsChromiteFarNorthMember 		Ìý
Permits [Member] Ìý Ìý Ìý
Goodwill [Line Items] Ìý Ìý Ìý
Impairment of Intangible Assets, Finite-lived 15.5us-gaap_ImpairmentOfIntangibleAssetsFinitelived
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_UseRightsMember 		Ìý Ìý
Utility Contracts [Member] Ìý Ìý Ìý
Goodwill [Line Items] Ìý Ìý Ìý
Impairment of Intangible Assets, Finite-lived Ìý $ 9.5us-gaap_ImpairmentOfIntangibleAssetsFinitelived
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= clf_UtilityContractsMember 		$ 0us-gaap_ImpairmentOfIntangibleAssetsFinitelived
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= clf_UtilityContractsMember