Annual report pursuant to Section 13 and 15(d)

Business Summary And Significant Accounting Policies (Inventories On The Statements Of Consolidated Financial Position) (Details)

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Business Summary And Significant Accounting Policies (Inventories On The Statements Of Consolidated Financial Position) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2011
Dec. 31, 2010
Inventory Finished Goods $ 291.3 $ 198.0
Work-in Process 184.4 71.2
Total Inventory 475.7 269.2
U.S. Iron Ore [Member]
    
Inventory Finished Goods 100.2 101.1
Work-in Process 8.5 9.7
Total Inventory 108.7 110.8
Eastern Canadian Iron Ore [Member]
    
Inventory Finished Goods 96.2 43.5
Work-in Process 43.0 21.2
Total Inventory 139.2 64.7
North American Coal [Member]
    
Inventory Finished Goods 19.7 16.1
Work-in Process 110.5 19.8
Total Inventory 130.2 35.9
Asia Pacific Iron Ore [Member]
    
Inventory Finished Goods 57.2 34.7
Work-in Process 21.6 20.4
Total Inventory 78.8 55.1
Other Segment [Member]
    
Inventory Finished Goods 18.0 2.6
Work-in Process 0.8 0.1
Total Inventory $ 18.8 $ 2.7