Annual report pursuant to Section 13 and 15(d)

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

v2.4.1.9
BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Schedule Of Subsidiaries) (Details)
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