Annual report pursuant to Section 13 and 15(d)

STOCK COMPENSATION PLANS STOCK COMPENSATION PLANS (Employee Plans) (Details)

v2.4.1.9
STOCK COMPENSATION PLANS STOCK COMPENSATION PLANS (Employee Plans) (Details) (Two Thousand Twelve Equity Plan [Member])
12 Months Ended
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Stock Issued During Period, Shares, Restricted Stock Award, Gross 300,000us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross
Maximum [Member]
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized 6,000,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_PlanNameAxis
= clf_TwoThousandTwelveEquityPlanMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
Additional Restricted Stock Awards for New Employees [Member]
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Stock Issued During Period, Shares, Restricted Stock Award, Gross 500,000us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross
/ us-gaap_AwardTypeAxis
= clf_AdditionalRestrictedStockAwardsforNewEmployeesMember
/ us-gaap_PlanNameAxis
= clf_TwoThousandTwelveEquityPlanMember