BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Revenue Reimbursement) (Details) (U.S. Iron Ore [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Reimbursement Revenue	$ 259.5	$ 250.8	$ 224.3
Freight Revenue [Member]
Reimbursement Revenue	177.3	142.0	128.4
Co-venturer [Member]
Reimbursement Revenue	$ 82.2	$ 108.8	$ 95.9