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STOCK COMPENSATION PLANS (Narrative) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified | 3 Months Ended
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Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Option Indexed to Issuer's Equity, Strike Price | $ 7.70 us-gaap_OptionIndexedToIssuersEquityStrikePrice1
2012 Equity Plan [Member] |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Performance/vesting period | 3 years
2015 to 2017 Performance Period [Member] | 2012 Equity Plan [Member] | Minimum [Member] |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Payout rate, as a percentage of the original grant | 0.00%clf_ShareBasedGoodsAndNonemployeeServicesTransactionValuationMethodPayoutRate / us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis = clf_A2015to2017PerformancePeriodMember / us-gaap_PlanNameAxis = clf_TwoThousandTwelveEquityPlanandAmendedEquityPlanMember / us-gaap_RangeAxis = us-gaap_MinimumMember
2015 to 2017 Performance Period [Member] | 2012 Equity Plan [Member] | Maximum [Member] |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Payout rate, as a percentage of the original grant | 200.00%clf_ShareBasedGoodsAndNonemployeeServicesTransactionValuationMethodPayoutRate / us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis = clf_A2015to2017PerformancePeriodMember / us-gaap_PlanNameAxis = clf_TwoThousandTwelveEquityPlanandAmendedEquityPlanMember / us-gaap_RangeAxis = us-gaap_MaximumMember
Performance Shares [Member] | 2012 Amended Equity Plan [Member] |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Number of performance shares granted | 0.9 us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross / us-gaap_AwardTypeAxis = us-gaap_PerformanceSharesMember / us-gaap_PlanNameAxis = clf_A2012AmendedEquityPlanMember
Employee Stock Option [Member] | 2012 Amended Equity Plan [Member] |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Number of performance shares granted | 0.4 us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = clf_A2012AmendedEquityPlanMember
Restricted Stock Units (RSUs) [Member] | 2012 Amended Equity Plan [Member] |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Number of restricted shares granted | 0.9 us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember / us-gaap_PlanNameAxis = clf_A2012AmendedEquityPlanMember

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- Definition Exercise or strike price stated in the contract for options indexed to the issuer's equity shares. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 480 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(1) -URI http://asc.fasb.org/extlink&oid=6940734&loc=d3e22047-110879 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 40 -Section 50 -Paragraph 5 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=6445032&loc=d3e90205-114008 + Details
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- Definition Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Total number of shares issued during the period, including shares forfeited, as a result of Restricted Stock Awards. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 + Details
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- Definition Gross number of shares (or other type of equity) issued during the period as a result of any equity-based compensation plan other than an employee stock ownership plan (ESOP). Shares issued could result from the issuance of restricted stock, the exercise of stock options, stock issued under employee stock purchase plans, and/or other employee benefit plans. + References No definition available. + Details
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