Annual report pursuant to Section 13 and 15(d)

STOCK COMPENSATION PLANS STOCK COMPENSATION PLANS (Incentive Plan Details) (Details)

v2.4.1.9
STOCK COMPENSATION PLANS STOCK COMPENSATION PLANS (Incentive Plan Details) (Details)
 3 Months Ended 12 Months Ended
Dec. 31, 2014
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Number of performance shares granted         2,016,996us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod    
Performance Shares [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Number of performance shares granted 400,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember 		283,530us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember 		124,630us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember 		385,585us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember 		1,233,685us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember 		806,271us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember 		501,346us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Estimated Forfeitures 40,911clf_SharebasedCompensationArrangementbySharebasedPaymentAwardNonOptionEquityInstrumentsEstimatedForfeitures
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember 		24,380clf_SharebasedCompensationArrangementbySharebasedPaymentAwardNonOptionEquityInstrumentsEstimatedForfeitures
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember 		21,098clf_SharebasedCompensationArrangementbySharebasedPaymentAwardNonOptionEquityInstrumentsEstimatedForfeitures
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember 		120,299clf_SharebasedCompensationArrangementbySharebasedPaymentAwardNonOptionEquityInstrumentsEstimatedForfeitures
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember 		     
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Expected to Vest 359,089clf_SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherthanOptionsExpectedtoVest
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember 		259,150clf_SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherthanOptionsExpectedtoVest
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember 		103,532clf_SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherthanOptionsExpectedtoVest
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember 		265,286clf_SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherthanOptionsExpectedtoVest
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember