Annual report pursuant to Section 13 and 15(d)

Goodwill And Other Intangible Assets And Liabilities (Schedule Of Goodwill) (Details)

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Goodwill And Other Intangible Assets And Liabilities (Schedule Of Goodwill) (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended 12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2011
Eastern Canadian Iron Ore [Member]
Dec. 31, 2010
Eastern Canadian Iron Ore [Member]
Dec. 31, 2011
U.S. Iron Ore [Member]
Dec. 31, 2010
U.S. Iron Ore [Member]
Dec. 31, 2009
U.S. Iron Ore [Member]
Dec. 31, 2011
Asia Pacific Iron Ore [Member]
Dec. 31, 2010
Asia Pacific Iron Ore [Member]
Dec. 31, 2011
North American Coal [Member]
Dec. 31, 2010
North American Coal [Member]
Dec. 31, 2010
Other [Member]
Dec. 31, 2011
Other [Member]
Region Reporting Information, by Region [Line Items]                          
Goodwill, beginning balance $ 196.5 $ 74.6 $ 3.1   $ 2.0 $ 2.0 $ 2.0 $ 82.6 $ 72.6 $ 27.9      $ 80.9
Arising in business combinations 983.4 111.9 983.5 3.1           (0.1) 27.9 80.9  
Impairment of goodwill (27.8)                 (27.8)       
Impact of foreign currency translation 0.4 10.0           0.4 10.0         
Other (0.4)   (0.4)                     
Goodwill, ending balance $ 1,152.1 $ 196.5 $ 986.2 $ 3.1 $ 2.0 $ 2.0 $ 2.0 $ 83.0 $ 82.6   $ 27.9 $ 80.9 $ 80.9