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
Dec. 31, 2012
Dec. 31, 2011
Goodwill [Roll Forward]    
Beginning Balance $ 1,152.1 $ 196.5
Arising in business combinations 13.8 983.4
Impairment (1,000.0) (27.8)
Impact of foreign currency translation 1.5 0.4
Other 0 (0.4)
Ending Balance 167.4 1,152.1
Goodwill, Impaired, Accumulated Impairment Loss (1,027.8) (27.8)
U.S. Iron Ore [Member]
    
Goodwill [Roll Forward]    
Beginning Balance 2.0 2.0
Arising in business combinations 0 0
Impairment 0 0
Impact of foreign currency translation 0 0
Other 0 0
Ending Balance 2.0 2.0
Goodwill, Impaired, Accumulated Impairment Loss 0 0
Eastern Canadian Iron Ore [Member]
    
Goodwill [Roll Forward]    
Beginning Balance 986.2 3.1
Arising in business combinations 13.8 983.5
Impairment (1,000.0) 0
Impact of foreign currency translation 0 0
Other 0 (0.4)
Ending Balance 0 986.2
Goodwill, Impaired, Accumulated Impairment Loss (1,000.0) 0
Asia Pacific Iron Ore [Member]
    
Goodwill [Roll Forward]    
Beginning Balance 83.0 82.6
Arising in business combinations 0 0
Impairment 0 0
Impact of foreign currency translation 1.5 0.4
Other 0 0
Ending Balance 84.5 83.0
Goodwill, Impaired, Accumulated Impairment Loss 0 0
North American Coal [Member]
    
Goodwill [Roll Forward]    
Beginning Balance 0 27.9
Arising in business combinations 0 (0.1)
Impairment 0 (27.8)
Impact of foreign currency translation 0 0
Other 0 0
Ending Balance 0 0
Goodwill, Impaired, Accumulated Impairment Loss (27.8) (27.8)
Other Segment [Member]
    
Goodwill [Roll Forward]    
Beginning Balance 80.9 80.9
Arising in business combinations 0 0
Impairment 0 0
Impact of foreign currency translation 0 0
Other 0 0
Ending Balance 80.9 80.9
Goodwill, Impaired, Accumulated Impairment Loss $ 0 $ 0