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Quarterly report pursuant to Section 13 or 15(d)

STOCK COMPENSATION PLANS (Narrative) (Details)

v2.4.1.9
STOCK COMPENSATION PLANS (Narrative) (Details) (USD $)
In Millions, except Per Share data, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Ìý
Option Indexed to Issuer's Equity, Strike Price $ 7.70us-gaap_OptionIndexedToIssuersEquityStrikePrice1
2012 Equity Plan [Member] Ìý
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Ìý
Performance/vesting period 3 years
2015 to 2017 Performance Period [Member] | 2012 Equity Plan [Member] | Minimum [Member] Ìý
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Ìý
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] Ìý
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Ìý
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] Ìý
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Ìý
Number of performance shares granted 0.9us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
/ us-gaap_PlanNameAxis
= clf_A2012AmendedEquityPlanMember
Employee Stock Option [Member] | 2012 Amended Equity Plan [Member] Ìý
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Ìý
Number of performance shares granted 0.4us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_PlanNameAxis
= clf_A2012AmendedEquityPlanMember
Restricted Stock Units (RSUs) [Member] | 2012 Amended Equity Plan [Member] Ìý
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Ìý
Number of restricted shares granted 0.9us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_PlanNameAxis
= clf_A2012AmendedEquityPlanMember