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Annual report pursuant to Section 13 and 15(d)

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

v2.4.1.9
RELATED PARTIES (Summary Of Other Ownership Interests) (Details)
Dec. 31, 2014
Dec. 31, 2012
Hibbing [Member] | Arcelor Mittal [Member] Ìý Ìý
Related Party Transaction [Line Items] Ìý Ìý
Ownership interest, equity method investment 62.30%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= clf_ArcelorMittalMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_HibbingMember 		Ìý
Hibbing [Member] | WISCO [Member] Ìý Ìý
Related Party Transaction [Line Items] Ìý Ìý
Ownership interest, equity method investment 0.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= clf_WiscoMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_HibbingMember 		Ìý
Hibbing [Member] | U. S. Steel Canada [Member] Ìý Ìý
Related Party Transaction [Line Items] Ìý Ìý
Ownership interest, equity method investment 14.70%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= clf_USSteelCanadaMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_HibbingMember 		Ìý
Empire [Member] Ìý Ìý
Related Party Transaction [Line Items] Ìý Ìý
Noncontrolling Interest, Ownership Percentage by Parent 79.00%us-gaap_MinorityInterestOwnershipPercentageByParent
/ clf_NameofOperationAxis
= clf_EmpireMember 		Ìý
Empire [Member] | Arcelor Mittal [Member] Ìý Ìý
Related Party Transaction [Line Items] Ìý Ìý
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners 21.00%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
/ clf_NameofOperationAxis
= clf_EmpireMember
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= clf_ArcelorMittalMember 		Ìý
Empire [Member] | WISCO [Member] Ìý Ìý
Related Party Transaction [Line Items] Ìý Ìý
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners 0.00%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
/ clf_NameofOperationAxis
= clf_EmpireMember
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= clf_WiscoMember 		Ìý
Empire [Member] | U. S. Steel Canada [Member] Ìý Ìý
Related Party Transaction [Line Items] Ìý Ìý
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners 0.00%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
/ clf_NameofOperationAxis
= clf_EmpireMember
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= clf_USSteelCanadaMember 		Ìý
Tilden [Member] Ìý Ìý
Related Party Transaction [Line Items] Ìý Ìý
Noncontrolling Interest, Ownership Percentage by Parent 85.00%us-gaap_MinorityInterestOwnershipPercentageByParent
/ clf_NameofOperationAxis
= clf_TildenMember 		Ìý
Tilden [Member] | Arcelor Mittal [Member] Ìý Ìý
Related Party Transaction [Line Items] Ìý Ìý
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners 0.00%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
/ clf_NameofOperationAxis
= clf_TildenMember
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= clf_ArcelorMittalMember 		Ìý
Tilden [Member] | WISCO [Member] Ìý Ìý
Related Party Transaction [Line Items] Ìý Ìý
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners 0.00%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
/ clf_NameofOperationAxis
= clf_TildenMember
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= clf_WiscoMember 		Ìý
Tilden [Member] | U. S. Steel Canada [Member] Ìý Ìý
Related Party Transaction [Line Items] Ìý Ìý
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners 15.00%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
/ clf_NameofOperationAxis
= clf_TildenMember
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= clf_USSteelCanadaMember 		Ìý
Bloom Lake [Member] Ìý Ìý
Related Party Transaction [Line Items] Ìý Ìý
Noncontrolling Interest, Ownership Percentage by Parent 82.80%us-gaap_MinorityInterestOwnershipPercentageByParent
/ clf_NameofOperationAxis
= clf_BloomLakeMember 		75.00%us-gaap_MinorityInterestOwnershipPercentageByParent
/ clf_NameofOperationAxis
= clf_BloomLakeMember
Bloom Lake [Member] | Arcelor Mittal [Member] Ìý Ìý
Related Party Transaction [Line Items] Ìý Ìý
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners 0.00%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
/ clf_NameofOperationAxis
= clf_BloomLakeMember
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= clf_ArcelorMittalMember 		Ìý
Bloom Lake [Member] | WISCO [Member] Ìý Ìý
Related Party Transaction [Line Items] Ìý Ìý
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners 17.20%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
/ clf_NameofOperationAxis
= clf_BloomLakeMember
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= clf_WiscoMember 		Ìý
Bloom Lake [Member] | U. S. Steel Canada [Member] Ìý Ìý
Related Party Transaction [Line Items] Ìý Ìý
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners 0.00%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
/ clf_NameofOperationAxis
= clf_BloomLakeMember
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= clf_USSteelCanadaMember 		Ìý
Investments in Ventures [Member] | Hibbing [Member] Ìý Ìý
Related Party Transaction [Line Items] Ìý Ìý
Ownership interest, equity method investment 23.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_BalanceSheetLocationAxis
= clf_InvestmentsinVenturesMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= clf_HibbingMember 		[1] Ìý
[1] 1 At December 31, 2013, the classification for Hibbing was Other liabilities.