Annual report pursuant to Section 13 and 15(d)

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Schedule Of Subsidiaries) (Details)

betfred sportsbook|Welcome_POLICIES (Narrative) ( v2.4.1.9
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12 Months Ended
Dec. 31, 2014
Dec. 31, 2012
Northshore [Member]    
Related Party Transaction [Line Items]    
Entity Address, State or Province Minnesota  
Noncontrolling Interest, Ownership Percentage by Parent 100.00%us-gaap_MinorityInterestOwnershipPercentageByParent
/ clf_NameofOperationAxis
= clf_NorthshoreMember
 
Segment Reporting Information, Description of Products and Services Iron Ore  
United Taconite [Member]    
Related Party Transaction [Line Items]    
Entity Address, State or Province Minnesota  
Noncontrolling Interest, Ownership Percentage by Parent 100.00%us-gaap_MinorityInterestOwnershipPercentageByParent
/ clf_NameofOperationAxis
= clf_UnitedTaconiteMember
 
Segment Reporting Information, Description of Products and Services Iron Ore  
Wabush [Member]    
Related Party Transaction [Line Items]    
Entity Address, State or Province Newfoundland and Labrador/ Québec, Canada  
Noncontrolling Interest, Ownership Percentage by Parent 100.00%us-gaap_MinorityInterestOwnershipPercentageByParent
/ clf_NameofOperationAxis
= clf_WabushMember
 
Segment Reporting Information, Description of Products and Services Iron Ore  
Bloom Lake [Member]    
Related Party Transaction [Line Items]    
Entity Address, State or Province Québec, Canada  
Noncontrolling Interest, Ownership Percentage by Parent 82.80%us-gaap_MinorityInterestOwnershipPercentageByParent
/ clf_NameofOperationAxis
= clf_BloomLakeMember
75.00%us-gaap_MinorityInterestOwnershipPercentageByParent
/ clf_NameofOperationAxis
= clf_BloomLakeMember
Segment Reporting Information, Description of Products and Services Iron Ore  
Tilden [Member]    
Related Party Transaction [Line Items]    
Entity Address, State or Province Michigan  
Noncontrolling Interest, Ownership Percentage by Parent 85.00%us-gaap_MinorityInterestOwnershipPercentageByParent
/ clf_NameofOperationAxis
= clf_TildenMember
 
Segment Reporting Information, Description of Products and Services Iron Ore  
Empire [Member]    
Related Party Transaction [Line Items]    
Entity Address, State or Province Michigan  
Noncontrolling Interest, Ownership Percentage by Parent 79.00%us-gaap_MinorityInterestOwnershipPercentageByParent
/ clf_NameofOperationAxis
= clf_EmpireMember
 
Segment Reporting Information, Description of Products and Services Iron Ore  
Koolyanobbing [Member]    
Related Party Transaction [Line Items]    
Entity Address, State or Province Western Australia  
Noncontrolling Interest, Ownership Percentage by Parent 100.00%us-gaap_MinorityInterestOwnershipPercentageByParent
/ clf_NameofOperationAxis
= clf_KoolyanobbingMember
 
Segment Reporting Information, Description of Products and Services Iron Ore  
Pinnacle [Member]    
Related Party Transaction [Line Items]    
Entity Address, State or Province West Virginia  
Noncontrolling Interest, Ownership Percentage by Parent 100.00%us-gaap_MinorityInterestOwnershipPercentageByParent
/ clf_NameofOperationAxis
= clf_PinnacleMember
 
Segment Reporting Information, Description of Products and Services Coal  
Oak Grove [Member]    
Related Party Transaction [Line Items]    
Entity Address, State or Province Alabama  
Noncontrolling Interest, Ownership Percentage by Parent 100.00%us-gaap_MinorityInterestOwnershipPercentageByParent
/ clf_NameofOperationAxis
= clf_OakGroveMember
 
Segment Reporting Information, Description of Products and Services Coal  
CLCC [Member]    
Related Party Transaction [Line Items]    
Entity Address, State or Province West Virginia  
Noncontrolling Interest, Ownership Percentage by Parent 100.00%us-gaap_MinorityInterestOwnershipPercentageByParent
/ clf_NameofOperationAxis
= clf_ClccMember
 
Segment Reporting Information, Description of Products and Services Coal  
Black Label Deposit [Member]    
Related Party Transaction [Line Items]    
Entity Address, State or Province Ontario, Canada  
Noncontrolling Interest, Ownership Percentage by Parent 100.00%us-gaap_MinorityInterestOwnershipPercentageByParent
/ clf_NameofOperationAxis
= clf_BlackLabelDepositMember
 
Segment Reporting Information, Description of Products and Services Chromite  
Black Thor Deposit [Member]    
Related Party Transaction [Line Items]    
Entity Address, State or Province Ontario, Canada  
Noncontrolling Interest, Ownership Percentage by Parent 100.00%us-gaap_MinorityInterestOwnershipPercentageByParent
/ clf_NameofOperationAxis
= clf_BlackThorDepositMember
 
Segment Reporting Information, Description of Products and Services Chromite  
Big Daddy Chromite Deposit [Member]    
Related Party Transaction [Line Items]    
Entity Address, State or Province Ontario, Canada  
Noncontrolling Interest, Ownership Percentage by Parent 70.00%us-gaap_MinorityInterestOwnershipPercentageByParent
/ clf_NameofOperationAxis
= clf_BigDaddyChromiteDepositMember
 
Segment Reporting Information, Description of Products and Services Chromite