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BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Schedule Of Subsidiaries) (Details)
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3 Months Ended |
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Mar. 31, 2015
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| Northshore [Member] |
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| 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/ Quebec, 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
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| Bloom Lake [Member] |
|
| Related Party Transaction [Line Items] |
|
| Entity Address, State or Province |
Quebec, Canada
|
| Noncontrolling Interest, Ownership Percentage by Parent |
82.80%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
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| 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
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| 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
|
| Black Label Deposit [Member] |
|
| Related Party Transaction [Line Items] |
|
| Entity Address, State or Province |
Ontario, Canada
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| Noncontrolling Interest, Ownership Percentage by Parent |
100.00%us-gaap_MinorityInterestOwnershipPercentageByParent
/ clf_NameofOperationAxis
= clf_BlackLabelDepositMember
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| Segment Reporting Information, Description of Products and Services |
Chromite
|
| Black Thor Deposit [Member] |
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| Related Party Transaction [Line Items] |
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| Entity Address, State or Province |
Ontario, Canada
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| Noncontrolling Interest, Ownership Percentage by Parent |
100.00%us-gaap_MinorityInterestOwnershipPercentageByParent
/ clf_NameofOperationAxis
= clf_BlackThorDepositMember
|
| Segment Reporting Information, Description of Products and Services |
Chromite
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| Big Daddy Chromite Deposit [Member] |
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| 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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