GOODWILL AND OTHER INTANGIBLE ASSETS AND LIABILITIES (Schedule Of Goodwill) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Goodwill [Roll Forward]
Beginning Balance	$ 1,152.1	$ 196.5
Arising in business combinations	13.8	983.4
Impairment	(1,000.0)	(27.8)
Impact of foreign currency translation	1.5	0.4
Other	0	(0.4)
Ending Balance	167.4	1,152.1
Goodwill, Impaired, Accumulated Impairment Loss	(1,027.8)	(27.8)
U.S. Iron Ore [Member]
Goodwill [Roll Forward]
Beginning Balance	2.0	2.0
Arising in business combinations	0	0
Impairment	0	0
Impact of foreign currency translation	0	0
Other	0	0
Ending Balance	2.0	2.0
Goodwill, Impaired, Accumulated Impairment Loss	0	0
Eastern Canadian Iron Ore [Member]
Goodwill [Roll Forward]
Beginning Balance	986.2	3.1
Arising in business combinations	13.8	983.5
Impairment	(1,000.0)	0
Impact of foreign currency translation	0	0
Other	0	(0.4)
Ending Balance	0	986.2
Goodwill, Impaired, Accumulated Impairment Loss	(1,000.0)	0
Asia Pacific Iron Ore [Member]
Goodwill [Roll Forward]
Beginning Balance	83.0	82.6
Arising in business combinations	0	0
Impairment	0	0
Impact of foreign currency translation	1.5	0.4
Other	0	0
Ending Balance	84.5	83.0
Goodwill, Impaired, Accumulated Impairment Loss	0	0
North American Coal [Member]
Goodwill [Roll Forward]
Beginning Balance	0	27.9
Arising in business combinations	0	(0.1)
Impairment	0	(27.8)
Impact of foreign currency translation	0	0
Other	0	0
Ending Balance	0	0
Goodwill, Impaired, Accumulated Impairment Loss	(27.8)	(27.8)
Other Segment [Member]
Goodwill [Roll Forward]
Beginning Balance	80.9	80.9
Arising in business combinations	0	0
Impairment	0	0
Impact of foreign currency translation	0	0
Other	0	0
Ending Balance	80.9	80.9
Goodwill, Impaired, Accumulated Impairment Loss	$ 0	$ 0