BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Reimbursements Revenue Disclosure) (Details) (U.S. Iron Ore [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Reimbursement Revenue, by Type [Line Items]
Reimbursement revenue	$ 250.8	$ 224.3	$ 223.4
Freight [Member]
Reimbursement Revenue, by Type [Line Items]
Reimbursement revenue	142.0	128.4	83.6
Venture Partners' Cost [Member]
Reimbursement Revenue, by Type [Line Items]
Reimbursement revenue	$ 108.8	$ 95.9	$ 139.8