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PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Annual Contributions To The Pension Plans) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Company contributions | $ 7.3 us-gaap_DefinedBenefitPlanContributionsByEmployer | $ 25.5 us-gaap_DefinedBenefitPlanContributionsByEmployer
Expected company contributions, next fiscal year | 6.8 us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear |
Funded percentage | 70.00%us-gaap_DefinedBenefitPlanFundedPercentage |
Value of VEBA Trust Assets as a Percentage of the Funding Obligation | 0.9 clf_ValueOfVebaTrustAssetsAsPercentageOfFundingObligation |
Pension Benefits [Member] |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Company contributions | 60.5 us-gaap_DefinedBenefitPlanContributionsByEmployer / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 53.7 us-gaap_DefinedBenefitPlanContributionsByEmployer / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember
Expected company contributions, next fiscal year | 36.8 us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |
Veba Trust [Member] |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Company contributions | 0 us-gaap_DefinedBenefitPlanContributionsByEmployer / clf_OtherBenefitsAxis = clf_VebaTrustMember | 14.6 us-gaap_DefinedBenefitPlanContributionsByEmployer / clf_OtherBenefitsAxis = clf_VebaTrustMember
Expected company contributions, next fiscal year | 0 us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear / clf_OtherBenefitsAxis = clf_VebaTrustMember |
Direct Payments [Member] |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Company contributions | 7.3 us-gaap_DefinedBenefitPlanContributionsByEmployer / clf_OtherBenefitsAxis = clf_DirectPaymentsMember | 10.9 us-gaap_DefinedBenefitPlanContributionsByEmployer / clf_OtherBenefitsAxis = clf_DirectPaymentsMember
Expected company contributions, next fiscal year | $ 6.8 us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear / clf_OtherBenefitsAxis = clf_DirectPaymentsMember |

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- Definition Value of VEBA Trust Assets as a Percentage of the Funding Obligation that causes the funding obligation to be suspended. + References No definition available. + Details
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Namespace Prefix: | clf_
Data Type: | xbrli:pureItemType
Balance Type: | na
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- Definition The increase in the fair value of plan assets from contributions made by the employer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition Plan assets of a defined benefit plan, as a percentage of projected benefit obligation. + References No definition available. + Details
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- Definition Amount of employer's best estimate of contributions expected to be paid to the plan during the next fiscal year beginning after the date of the latest statement of financial position. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Details
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- Details
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