Annual report pursuant to Section 13 and 15(d)

SEGMENT REPORTING SEGMENT REPORTING (Revenue from External Customers by Products and Services) (Details)

v2.4.1.9
SEGMENT REPORTING SEGMENT REPORTING (Revenue from External Customers by Products and Services) (Details) (Sales Revenue, Net [Member], Product Concentration Risk [Member])
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Revenue from External Customer [Line Items]      
Concentration Risk, Percentage 100.00%us-gaap_ConcentrationRiskPercentage1 100.00%us-gaap_ConcentrationRiskPercentage1 100.00%us-gaap_ConcentrationRiskPercentage1
Iron Ore Revenue [Member]
      
Revenue from External Customer [Line Items]      
Concentration Risk, Percentage 78.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_ProductConcentrationRiskMember
/ clf_RevenueTypeAxis
= clf_IronOreRevenueMember 		80.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_ProductConcentrationRiskMember
/ clf_RevenueTypeAxis
= clf_IronOreRevenueMember 		81.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_ProductConcentrationRiskMember
/ clf_RevenueTypeAxis
= clf_IronOreRevenueMember
Coal Revenue [Member]
      
Revenue from External Customer [Line Items]      
Concentration Risk, Percentage 12.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_ProductConcentrationRiskMember
/ clf_RevenueTypeAxis
= clf_CoalRevenueMember 		13.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_ProductConcentrationRiskMember
/ clf_RevenueTypeAxis
= clf_CoalRevenueMember 		13.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_ProductConcentrationRiskMember
/ clf_RevenueTypeAxis
= clf_CoalRevenueMember
Freight and Venture Partners' Cost Reimbursements [Member]
      
Revenue from External Customer [Line Items]      
Concentration Risk, Percentage 10.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_ProductConcentrationRiskMember
/ clf_RevenueTypeAxis
= clf_FreightAndVenturePartnersCostReimbursementsMember 		7.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_ProductConcentrationRiskMember
/ clf_RevenueTypeAxis
= clf_FreightAndVenturePartnersCostReimbursementsMember 		6.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_ProductConcentrationRiskMember
/ clf_RevenueTypeAxis
= clf_FreightAndVenturePartnersCostReimbursementsMember