Quarterly report pursuant to Section 13 or 15(d)

Acquisitions And Other Investments (Schedule Of Unaudited Consolidated Proforma Information) (Details)

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Acquisitions And Other Investments (Schedule Of Unaudited Consolidated Proforma Information) (Details) (Consolidated Thompson [Member], USD $)
In Millions, except Per Share data, unless otherwise specified
3 Months Ended
Mar. 31, 2011
Consolidated Thompson [Member]
 
Business Acquisition [Line Items]  
REVENUES FROM PRODUCT SALES AND SERVICES $ 1,278.8
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS $ 400.1
EARNINGS PER COMMON SHARE ATTRIBUTABLE TO CLIFFS SHAREHOLDERS - BASIC $ 2.95
EARNINGS PER COMMON SHARE ATTRIBUTABLE TO CLIFFS SHAREHOLDERS - DILUTED $ 2.94