Quarterly report pursuant to Section 13 or 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
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Goodwill [Line Items]    
Below Market Sales Contract, Remaining Life 2 years  
Product $ 399.5us-gaap_SalesRevenueGoodsNet $ 559.2us-gaap_SalesRevenueGoodsNet
Cost of Sales [Member]    
Goodwill [Line Items]    
Amortization expense relating to intangible assets 1.1us-gaap_AmortizationOfIntangibleAssets
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember
2.3us-gaap_AmortizationOfIntangibleAssets
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_CostOfSalesMember
Product Revenues [Member] | Sales Revenue, Goods, Net [Member]    
Goodwill [Line Items]    
Product $ 0us-gaap_SalesRevenueGoodsNet
/ clf_BelowMarketSalesContractsAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_SalesRevenueGoodsNetMember