Annual report pursuant to Section 13 and 15(d)

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Investments In Unconsolidated Ventures) (Details)

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12 Months Ended
Dec. 31, 2014
USD ($)
Dec. 31, 2013
USD ($)
Dec. 31, 2014
Asia Pacific Iron Ore [Member]
Facility
Dec. 31, 2013
Asia Pacific Iron Ore [Member]
Cockatoo [Member]
AUD
Dec. 31, 2013
Investments in Ventures [Member]
Amapa [Member]
Dec. 31, 2014
Investments in Ventures [Member]
Hibbing [Member]
Dec. 31, 2014
Investments in Ventures [Member]
Other Equity Investees [Member]
USD ($)
Dec. 31, 2013
Investments in Ventures [Member]
Other Equity Investees [Member]
USD ($)
Dec. 31, 2014
Other Noncurrent Liabilities [Member]
Hibbing [Member]
USD ($)
Dec. 31, 2013
Other Noncurrent Liabilities [Member]
Hibbing [Member]
USD ($)
Schedule of Equity Method Investments [Line Items]                    
Ownership interest, equity method investment         30.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_BalanceSheetLocationAxis
= clf_InvestmentsinVenturesMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_AmapaMember
23.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_BalanceSheetLocationAxis
= clf_InvestmentsinVenturesMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_HibbingMember
[1]        
Total percentage of Amapa sold         100.00%clf_TotalPercentageOfAmapaSold
/ us-gaap_BalanceSheetLocationAxis
= clf_InvestmentsinVenturesMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_AmapaMember
         
Investment $ 7,000,000us-gaap_EquityMethodInvestments $ 30,800,000us-gaap_EquityMethodInvestments         $ 3,900,000us-gaap_EquityMethodInvestments
/ us-gaap_BalanceSheetLocationAxis
= clf_InvestmentsinVenturesMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_OtherEquityInvesteesMember
$ 34,700,000us-gaap_EquityMethodInvestments
/ us-gaap_BalanceSheetLocationAxis
= clf_InvestmentsinVenturesMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_OtherEquityInvesteesMember
$ 3,100,000us-gaap_EquityMethodInvestments
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_OtherNoncurrentLiabilitiesMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_HibbingMember
[1] $ (3,900,000)us-gaap_EquityMethodInvestments
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_OtherNoncurrentLiabilitiesMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_HibbingMember
[1]
Proceeds from sale of economic interest (in AUD)       4.00us-gaap_ProceedsFromDivestitureOfInterestInJointVenture
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_CockatooMember
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
           
Number Of Mines     1clf_NumberOfMines
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
             
[1] 1 At December 31, 2013, the classification for Hibbing was Other liabilities.