Annual report pursuant to Section 13 and 15(d)

STOCK COMPENSATION PLANS (Share-based Compensation Expense Recorded For Continuing Operations) (Details)

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STOCK COMPENSATION PLANS (Share-based Compensation Expense Recorded For Continuing Operations) (Details) (USD $)
In Millions, except Per Share data, unless otherwise specified
3 Months Ended 12 Months Ended
Dec. 31, 2012
Sep. 30, 2012
Jun. 30, 2012
Mar. 31, 2012
Dec. 31, 2011
Sep. 30, 2011
Jun. 30, 2011
Mar. 31, 2011
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]                      
Selling, general and administrative expenses                 $ 282.5 $ 248.3 $ 171.7
Reduction of operating income from continuing operations before income taxes and equity income (loss) from ventures                 (501.8) 2,190.5 1,266.4
Income tax benefit                 255.9 407.7 282.5
NET INCOME (LOSS) ATTRIBUTABLE TO CLIFFS SHAREHOLDERS (1,618.3) 85.1 258.0 375.8 185.4 601.2 409.1 423.4 (899.4) 1,619.1 1,019.9
Reduction of earnings per share attributable to Cliffs shareholders:                      
Basic (in usd per share) $ (11.36) $ 0.60 $ 1.81 $ 2.64 $ 1.30 $ 4.17 $ 2.94 $ 3.12 $ (6.32) $ 11.55 $ 7.54
Diluted (in usd per share) $ (11.36) $ 0.59 $ 1.81 $ 2.63 $ 1.30 $ 4.15 $ 2.92 $ 3.11 $ (6.32) $ 11.48 $ 7.49
Deferred Compensation, Share-based Payments [Member]
                     
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]                      
Cost of goods sold and operating expenses                 4.0 2.7 2.8
Selling, general and administrative expenses                 16.6 13.2 12.7
Reduction of operating income from continuing operations before income taxes and equity income (loss) from ventures                 20.6 15.9 15.5
Income tax benefit                 (7.2) (5.6) (5.4)
NET INCOME (LOSS) ATTRIBUTABLE TO CLIFFS SHAREHOLDERS                 $ 13.4 $ 10.3 $ 10.1
Reduction of earnings per share attributable to Cliffs shareholders:                      
Basic (in usd per share)                 $ 0.09 $ 0.07 $ 0.07
Diluted (in usd per share)                 $ 0.09 $ 0.07 $ 0.07