Quarterly report pursuant to Section 13 or 15(d)

INVENTORIES (Schedule Of Inventories) (Details)

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INVENTORIES (Schedule Of Inventories) (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 6 Months Ended
Jun. 30, 2013
Dec. 31, 2012
Jun. 30, 2013
U.S. Iron Ore [Member]
Dec. 31, 2012
U.S. Iron Ore [Member]
Jun. 30, 2013
Eastern Canadian Iron Ore [Member]
Dec. 31, 2012
Eastern Canadian Iron Ore [Member]
Jun. 30, 2013
Asia Pacific Iron Ore [Member]
Dec. 31, 2012
Asia Pacific Iron Ore [Member]
Jun. 30, 2013
North American Coal [Member]
Dec. 31, 2012
North American Coal [Member]
Jun. 30, 2013
Cost Of Goods Sold And Operating Expenses [Member]
North American Coal [Member]
Jun. 30, 2012
Cost Of Goods Sold And Operating Expenses [Member]
North American Coal [Member]
Jun. 30, 2013
Cost Of Goods Sold And Operating Expenses [Member]
North American Coal [Member]
Jun. 30, 2012
Cost Of Goods Sold And Operating Expenses [Member]
North American Coal [Member]
Jun. 30, 2013
Sinter feed [Member]
Wabush [Member]
Cost Of Goods Sold And Operating Expenses [Member]
Jun. 30, 2013
Pellets [Member]
Wabush [Member]
Cost Of Goods Sold And Operating Expenses [Member]
Inventory, Net [Abstract]                                
Finished Goods $ 427.9 $ 283.2 $ 242.1 $ 147.2 $ 94.0 $ 62.6 $ 51.6 $ 36.7 $ 40.2 $ 36.7            
Work-in Process 101.3 153.3 22.2 22.9 36.5 44.2 28.4 37.2 14.2 49.0            
Total Inventory 529.2 436.5 264.3 170.1 130.5 106.8 80.0 73.9 54.4 85.7            
Lower-of-cost-or-market inventory charges                     0.7 8.6 2.7 9.9 4.7 11.1
Unsaleable Inventory Impairment Charge                               $ 10.6