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Quarterly report pursuant to Section 13 or 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
3 Months Ended 12 Months Ended
Mar. 31, 2015
Dec. 31, 2014
Goodwill [Roll Forward] Ìý Ìý
Beginning Balance $ 2.0us-gaap_Goodwill $ 74.5us-gaap_Goodwill
Arising in business combinations 0us-gaap_GoodwillAcquiredDuringPeriod 0us-gaap_GoodwillAcquiredDuringPeriod
Impairment 0us-gaap_GoodwillImpairmentLoss (73.5)us-gaap_GoodwillImpairmentLoss
Impact of foreign currency translation 0us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments 1.0us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments
Ending Balance 2.0us-gaap_Goodwill 2.0us-gaap_Goodwill
Accumulated goodwill impairment loss (73.5)us-gaap_GoodwillImpairedAccumulatedImpairmentLoss (73.5)us-gaap_GoodwillImpairedAccumulatedImpairmentLoss
U.S. Iron Ore [Member] Ìý Ìý
Goodwill [Roll Forward] Ìý Ìý
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
Asia Pacific Iron Ore [Member] Ìý Ìý
Goodwill [Roll Forward] Ìý Ìý
Beginning Balance 0us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
72.5us-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 0us-gaap_GoodwillImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
(73.5)us-gaap_GoodwillImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
Impact of foreign currency translation 0us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
1.0us-gaap_GoodwillTranslationAndPurchaseAccountingAdjustments
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
Ending Balance 0us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
0us-gaap_Goodwill
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
Accumulated goodwill impairment loss $ (73.5)us-gaap_GoodwillImpairedAccumulatedImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember
$ (73.5)us-gaap_GoodwillImpairedAccumulatedImpairmentLoss
/ us-gaap_StatementBusinessSegmentsAxis
= clf_AsiaPacificIronOreMember