Quarterly report pursuant to Section 13 or 15(d)

Inventories (Detail of Inventories) (Details)

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Inventories (Detail of Inventories) (Details) (USD $)
In Millions
Jun. 30, 2011
Dec. 31, 2010
Finished Goods $ 512.2 $ 198.0
Work-in Process 93.1 71.2
Total Inventory 605.3 269.2
U.S. Iron Ore [Member]
    
Finished Goods 317.1 101.1
Work-in Process 18.8 9.7
Total Inventory 335.9 110.8
Eastern Canadian Iron Ore [Member]
    
Finished Goods 147.5 43.5
Work-in Process 35.3 21.2
Total Inventory 182.8 64.7
North American Coal [Member]
    
Finished Goods 5.0 16.1
Work-in Process 23.0 19.8
Total Inventory 28.0 35.9
Asia Pacific Iron Ore [Member]
    
Finished Goods 37.7 34.7
Work-in Process 14.5 20.4
Total Inventory 52.2 55.1
Other Segment [Member]
    
Finished Goods 4.9 2.6
Work-in Process 1.5 0.1
Total Inventory $ 6.4 $ 2.7