Annual report pursuant to Section 13 and 15(d)

Quarterly Results of Operations (Schedule Of Quarterly Financial Information) (Details)

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Quarterly Results of Operations (Schedule Of Quarterly Financial Information) (Details) (USD $)
In Millions, except Per Share data, unless otherwise specified
3 Months Ended 12 Months Ended
Dec. 31, 2011
Sep. 30, 2011
Jun. 30, 2011
Mar. 31, 2011
Dec. 31, 2010
Sep. 30, 2010
Jun. 30, 2010
Mar. 31, 2010
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Quarterly Results Of Operations (Unaudited) [Abstract]                      
Revenues from product sales and services $ 1,662.5 $ 2,142.8 $ 1,805.8 $ 1,183.2 $ 1,424.1 $ 1,346.0 $ 1,184.3 $ 727.7 $ 6,794.3 $ 4,682.1 $ 2,342.0
Sales margin 496.2 861.3 731.6 599.5 483.5 477.3 415.2 150.5 2,688.6 1,526.5 311.7
Net income from continuing operations attributable to Cliffs shareholders 185.3 618.7 409.8 423.8 385.2 298.3 261.5 78.0 1,637.6 1,023.0 208.5
Loss from discontinued operations 0.1 (17.5) (0.7) (0.4) (1.1) (0.7) (0.7) (0.6) (18.5) (3.1) (3.4)
Net income (loss) attributable to Cliffs shareholders 185.4 601.2 409.1 423.4 384.1 297.6 260.8 77.4 1,619.1 1,019.9 205.1
LOSS FROM DISCONTINUED OPERATIONS, net of tax $ 0.1 $ (17.5) $ (0.7) $ (0.4) $ (1.1) $ (0.7) $ (0.7) $ (0.6) $ (18.5) $ (3.1) $ (3.4)
Earnings Per Share [Abstract]                      
Continuing operations $ 1.30 $ 4.29 $ 2.95 $ 3.12 $ 2.85 $ 2.20 $ 1.93 $ 0.58 $ 11.68 $ 7.56 $ 1.67
Discontinued operations   $ (0.12) $ (0.01)   $ (0.01) $ (0.01)     $ (0.13) $ (0.02) $ (0.03)
Earnings per common share attributable to Cliffs shareholders - Basic: $ 1.30 $ 4.17 $ 2.94 $ 3.12 $ 2.84 $ 2.19 $ 1.93 $ 0.58 $ 11.55 $ 7.54 $ 1.64
Continuing operations $ 1.30 $ 4.27 $ 2.93 $ 3.11 $ 2.83 $ 2.19 $ 1.92 $ 0.57 $ 11.61 $ 7.51 $ 1.66
Discontinued operations   $ (0.12) $ (0.01)   $ (0.01) $ (0.01)     $ (0.13) $ (0.02) $ (0.03)
Earnings per common share attributable to Cliffs shareholders - Diluted: $ 1.30 $ 4.15 $ 2.92 $ 3.11 $ 2.82 $ 2.18 $ 1.92 $ 0.57 $ 11.48 $ 7.49 $ 1.63