Quarterly report pursuant to Section 13 or 15(d)

RELATED PARTIES (Summary Of Other Ownership Interests) (Details)

v2.4.1.9
RELATED PARTIES (Summary Of Other Ownership Interests) (Details)
Mar. 31, 2015
Hibbing [Member] | Arcelor Mittal [Member]  
Related Party Transaction [Line Items]  
Ownership interest, equity method investment 62.30%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= clf_ArcelorMittalMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_HibbingMember
Hibbing [Member] | U. S. Steel Canada [Member]  
Related Party Transaction [Line Items]  
Ownership interest, equity method investment 14.70%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= clf_USSteelCanadaMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_HibbingMember
Empire [Member]  
Related Party Transaction [Line Items]  
Noncontrolling Interest, Ownership Percentage by Parent 79.00%us-gaap_MinorityInterestOwnershipPercentageByParent
/ clf_NameofOperationAxis
= clf_EmpireMember
Empire [Member] | Arcelor Mittal [Member]  
Related Party Transaction [Line Items]  
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners 21.00%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
/ clf_NameofOperationAxis
= clf_EmpireMember
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= clf_ArcelorMittalMember
Empire [Member] | U. S. Steel Canada [Member]  
Related Party Transaction [Line Items]  
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners 0.00%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
/ clf_NameofOperationAxis
= clf_EmpireMember
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= clf_USSteelCanadaMember
Tilden [Member]  
Related Party Transaction [Line Items]  
Noncontrolling Interest, Ownership Percentage by Parent 85.00%us-gaap_MinorityInterestOwnershipPercentageByParent
/ clf_NameofOperationAxis
= clf_TildenMember
Tilden [Member] | Arcelor Mittal [Member]  
Related Party Transaction [Line Items]  
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners 0.00%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
/ clf_NameofOperationAxis
= clf_TildenMember
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= clf_ArcelorMittalMember
Tilden [Member] | U. S. Steel Canada [Member]  
Related Party Transaction [Line Items]  
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners 15.00%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
/ clf_NameofOperationAxis
= clf_TildenMember
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= clf_USSteelCanadaMember
Bloom Lake [Member]  
Related Party Transaction [Line Items]  
Noncontrolling Interest, Ownership Percentage by Parent 82.80%us-gaap_MinorityInterestOwnershipPercentageByParent
/ clf_NameofOperationAxis
= clf_BloomLakeMember
Other Noncurrent Assets [Member] | Hibbing [Member]  
Related Party Transaction [Line Items]  
Ownership interest, equity method investment 23.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_OtherNoncurrentAssetsMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_HibbingMember