ENVIRONMENTAL AND MINE CLOSURE OBLIGATIONS (Summary Of Mine Closure Obligations) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Loss Contingencies [Line Items]
Environmental	$ 8.4	$ 15.7
Mine Reclamation and Closing Liability, current and noncurrent	301.8	249.4
Total environmental and mine closure obligations	310.2	265.1
Less current portion	10.7	12.3
Long term environmental and mine closure obligations	299.5	252.8
U.S. Iron Ore [Member] | Owned Or Operating Facilities [Member]
Loss Contingencies [Line Items]
Mine Reclamation and Closing Liability, current and noncurrent	139.6	81.2
Eastern Canadian Iron Ore [Member] | Owned Or Operating Facilities [Member]
Loss Contingencies [Line Items]
Mine Reclamation and Closing Liability, current and noncurrent	76.6	88.9
Asia Pacific Iron Ore [Member] | Owned Or Operating Facilities [Member]
Loss Contingencies [Line Items]
Mine Reclamation and Closing Liability, current and noncurrent	26.2	22.4
North American Coal [Member] | Owned Or Operating Facilities [Member]
Loss Contingencies [Line Items]
Mine Reclamation and Closing Liability, current and noncurrent	40.0	38.6
LTV Steel Mining Company [Member] | Previously Owned Or Operating Facilities [Member]
Loss Contingencies [Line Items]
Mine Reclamation and Closing Liability, current and noncurrent	$ 19.4	$ 18.3