Annual report pursuant to Section 13 and 15(d)

GOODWILL AND OTHER INTANGIBLE ASSETS AND LIABILITIES (Schedule Of Goodwill) (Details)

v2.4.1.9
GOODWILL AND OTHER INTANGIBLE ASSETS AND LIABILITIES (Schedule Of Goodwill) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Goodwill [Roll Forward]    
Beginning Balance $ 74.5us-gaap_Goodwill $ 167.4us-gaap_Goodwill
Arising in business combinations 0us-gaap_GoodwillAcquiredDuringPeriod 0us-gaap_GoodwillAcquiredDuringPeriod
Impairment (73.5)us-gaap_GoodwillImpairmentLoss (80.9)us-gaap_GoodwillImpairmentLoss
Impact of foreign currency translation 1.0us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments (12.0)us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments
Ending Balance 2.0us-gaap_Goodwill 74.5us-gaap_Goodwill
Accumulated Goodwill Impairment Loss (1,154.4)us-gaap_GoodwillImpairedAccumulatedImpairmentLoss (1,080.9)us-gaap_GoodwillImpairedAccumulatedImpairmentLoss
U.S. Iron Ore [Member]    
Goodwill [Roll Forward]    
Beginning Balance 2.0us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
2.0us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
Arising in business combinations 0us-gaap_GoodwillAcquiredDuringPeriod
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
0us-gaap_GoodwillAcquiredDuringPeriod
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
Impairment 0us-gaap_GoodwillImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
0us-gaap_GoodwillImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
Impact of foreign currency translation 0us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
0us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
Ending Balance 2.0us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
2.0us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
Accumulated Goodwill Impairment Loss 0us-gaap_GoodwillImpairedAccumulatedImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
0us-gaap_GoodwillImpairedAccumulatedImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= clf_USIronOreMember
Eastern Canadian Iron Ore [Member]    
Goodwill [Roll Forward]    
Beginning Balance 0us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember
0us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember
Arising in business combinations 0us-gaap_GoodwillAcquiredDuringPeriod
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember
0us-gaap_GoodwillAcquiredDuringPeriod
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember
Impairment 0us-gaap_GoodwillImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember
0us-gaap_GoodwillImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember
Impact of foreign currency translation 0us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember
0us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember
Ending Balance 0us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember
0us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember
Accumulated Goodwill Impairment Loss (1,000.0)us-gaap_GoodwillImpairedAccumulatedImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember
(1,000.0)us-gaap_GoodwillImpairedAccumulatedImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= clf_EasternCanadianIronOreMember
Asia Pacific Iron Ore [Member]    
Goodwill [Roll Forward]    
Beginning Balance 72.5us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
84.5us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
Arising in business combinations 0us-gaap_GoodwillAcquiredDuringPeriod
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
0us-gaap_GoodwillAcquiredDuringPeriod
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
Impairment (73.5)us-gaap_GoodwillImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
0us-gaap_GoodwillImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
Impact of foreign currency translation 1.0us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
(12.0)us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
Ending Balance 0us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
72.5us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
Accumulated Goodwill Impairment Loss (73.5)us-gaap_GoodwillImpairedAccumulatedImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
0us-gaap_GoodwillImpairedAccumulatedImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
Other Segment [Member]    
Goodwill [Roll Forward]    
Beginning Balance 0us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= clf_OtherSegmentMember
80.9us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= clf_OtherSegmentMember
Arising in business combinations 0us-gaap_GoodwillAcquiredDuringPeriod
/ us-gaap_StatementBusinessSegmentsAxis
= clf_OtherSegmentMember
0us-gaap_GoodwillAcquiredDuringPeriod
/ us-gaap_StatementBusinessSegmentsAxis
= clf_OtherSegmentMember
Impairment   80.9us-gaap_GoodwillImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= clf_OtherSegmentMember
Impact of foreign currency translation 0us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments
/ us-gaap_StatementBusinessSegmentsAxis
= clf_OtherSegmentMember
0us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments
/ us-gaap_StatementBusinessSegmentsAxis
= clf_OtherSegmentMember
Ending Balance 0us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= clf_OtherSegmentMember
0us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= clf_OtherSegmentMember
Accumulated Goodwill Impairment Loss (80.9)us-gaap_GoodwillImpairedAccumulatedImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= clf_OtherSegmentMember
(80.9)us-gaap_GoodwillImpairedAccumulatedImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= clf_OtherSegmentMember
Other Segment [Member]    
Goodwill [Roll Forward]    
Impairment $ 0us-gaap_GoodwillImpairmentLoss
/ clf_ReportingUnitAxis
= clf_OtherSegmentMember