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BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Schedule of Intangible Asset Lives) (Details) | 12 Months Ended |
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Dec. 31, 2014 | Dec. 31, 2013
All Other Segments [Member] | Permits [Member] | Minimum [Member] |  |
Finite-Lived Intangible Assets [Line Items] |  |
Finite-Lived Intangible Asset, Useful Life | 15 years |
All Other Segments [Member] | Permits [Member] | Maximum [Member] |  |
Finite-Lived Intangible Assets [Line Items] |  |
Finite-Lived Intangible Asset, Useful Life | 40 years |
All Other Segments [Member] | Utility Contracts [Member] |  |
Finite-Lived Intangible Assets [Line Items] |  |
Finite-Lived Intangible Asset, Useful Life | 5 years |
All Other Segments [Member] | Leases [Member] | Minimum [Member] |  |
Finite-Lived Intangible Assets [Line Items] |  |
Finite-Lived Intangible Asset, Useful Life | 4 years 6 months |
All Other Segments [Member] | Leases [Member] | Maximum [Member] |  |
Finite-Lived Intangible Assets [Line Items] |  |
Finite-Lived Intangible Asset, Useful Life | 17 years 6 months |
Amapa [Member] | Investments in Ventures [Member] |  |
Finite-Lived Intangible Assets [Line Items] |  |
Ownership interest, equity method investment |  | 30.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_BalanceSheetLocationAxis = clf_InvestmentsinVenturesMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = clf_AmapaMember

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- Definition The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571 + Details
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- Details
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- Definition Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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- Details
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Balance Type: |
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