| GOODWILL AND OTHER INTANGIBLE ASSETS AND LIABILITIES (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended | |
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| 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 | |
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- Definition Below Market Sales Contract, Remaining Life No definition available. 
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- Definition The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Aggregate revenue during the period from the sale of goods in the normal course of business, after deducting returns, allowances and discounts. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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