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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 |

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- Definition Description of the types of products and services from which the reportable segment derives its revenue. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 21 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8721-108599 + Details
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Name: | clf_NameofOperationAxis=clf_BlackLabelDepositMember
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Name: | clf_NameofOperationAxis=clf_BlackThorDepositMember
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- Details
Name: | clf_NameofOperationAxis=clf_BloomLakeMember
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Name: | clf_NameofOperationAxis=clf_ClccMember
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Name: | clf_NameofOperationAxis=clf_EmpireMember
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Name: | clf_NameofOperationAxis=clf_KoolyanobbingMember
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Name: | clf_NameofOperationAxis=clf_NorthshoreMember
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Name: | clf_NameofOperationAxis=clf_UnitedTaconiteMember
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Name: | clf_NameofOperationAxis=clf_WabushMember
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