Environmental And Mine Closure Obligations (Summary Of Mine Closure Obligations) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Loss Contingencies [Line Items]
Environmental	$ 15.5	$ 15.5
Total mine closure	225.2	220.2
Total environmental and mine closure obligations	240.7	235.7
Less current portion	13.7	13.7
Long term environmental and mine closure obligations	227.0	222.0
Previously Owned or Operating Facilities [Member] | LTV Steel Mining Company [Member]
Loss Contingencies [Line Items]
Total mine closure	16.7	16.5
Owned or Operating Facilities [Member] | U.S. Iron Ore [Member]
Loss Contingencies [Line Items]
Total mine closure	76.1	74.3
Owned or Operating Facilities [Member] | Eastern Canadian Iron Ore [Member]
Loss Contingencies [Line Items]
Total mine closure	69.8	68.0
Owned or Operating Facilities [Member] | North American Coal [Member]
Loss Contingencies [Line Items]
Total mine closure	36.9	36.3
Owned or Operating Facilities [Member] | Asia Pacific Iron Ore [Member]
Loss Contingencies [Line Items]
Total mine closure	16.7	16.3
Owned or Operating Facilities [Member] | Other Regions [Member]
Loss Contingencies [Line Items]
Total mine closure	$ 9.0	$ 8.8