Quarterly report pursuant to Section 13 or 15(d)

Earnings Per Share (Calculation Of Earnings Per Common Share On Basic And Diluted) (Details)

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Earnings Per Share (Calculation Of Earnings Per Common Share On Basic And Diluted) (Details) (USD $)
In Millions, except Share data
3 Months Ended 9 Months Ended
Sep. 30, 2011
Sep. 30, 2010
Sep. 30, 2011
Sep. 30, 2010
Earnings Per Share [Abstract]        
Net income from continuing operations attributable to Cliffs shareholders $ 607.0 $ 298.1 $ 1,439.3 $ 637.4
Loss from discontinued operations (17.5) (0.7) (18.7) (2.0)
NET INCOME ATTRIBUTABLE TO CLIFFS SHAREHOLDERS $ 589.5 $ 297.4 $ 1,420.6 $ 635.4
Weighted average number of shares:        
Basic 144,203,000 135,345,000 139,563,000 135,280,000
Employee stock plans 800,000 900,000 800,000 800,000
Diluted 144,989,000 136,213,000 140,321,000 136,098,000
Continuing operations $ 4.21 $ 2.20 $ 10.31 $ 4.71
Discontinued operations $ (0.12)   $ (0.13) $ (0.01)
Earnings per common share attributable to Cliffs shareholders - Basic $ 4.09 $ 2.20 $ 10.18 $ 4.70
Continuing operations $ 4.19 $ 2.19 $ 10.25 $ 4.68
Discontinued operations $ (0.12) $ (0.01) $ (0.13) $ (0.01)
Earnings per common share attributable to Cliffs shareholders - Diluted $ 4.07 $ 2.18 $ 10.12 $ 4.67