Quarterly report pursuant to Section 13 or 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
 3 Months Ended 12 Months Ended
Mar. 31, 2014
Dec. 31, 2013
Goodwill [Roll Forward]    
Beginning Balance $ 74.5 $ 167.4
Arising in business combinations 0 0
Impairment 0 (80.9)
Impact of foreign currency translation 2.8 (12.0)
Ending Balance 77.3 74.5
Accumulated goodwill impairment loss (1,108.7) (1,108.7)
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
Ending Balance 2.0 2.0
Accumulated goodwill impairment loss 0 0
Eastern Canadian Iron Ore [Member]
    
Goodwill [Roll Forward]    
Beginning Balance 0 0
Arising in business combinations 0 0
Impairment 0 0
Impact of foreign currency translation 0 0
Ending Balance 0 0
Accumulated goodwill impairment loss (1,000.0) (1,000.0)
Asia Pacific Iron Ore [Member]
    
Goodwill [Roll Forward]    
Beginning Balance 72.5 84.5
Arising in business combinations 0 0
Impairment 0 0
Impact of foreign currency translation 2.8 (12.0)
Ending Balance 75.3 72.5
Accumulated goodwill impairment loss 0 0
North American Coal [Member]
    
Goodwill [Roll Forward]    
Beginning Balance 0 0
Arising in business combinations 0 0
Impairment 0 0
Impact of foreign currency translation 0 0
Ending Balance 0 0
Accumulated goodwill impairment loss (27.8) (27.8)
Other Segment [Member]
    
Goodwill [Roll Forward]    
Beginning Balance 0 80.9
Arising in business combinations 0 0
Impairment 0 (80.9)
Impact of foreign currency translation 0 0
Ending Balance 0 0
Accumulated goodwill impairment loss $ (80.9) $ (80.9)