BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Schedule Of Subsidiaries) (Details)	3 Months Ended
	Mar. 31, 2018
Northshore [Member]
Related Party Transaction [Line Items]
Entity Address, State or Province	Minnesota
United Taconite [Member]
Related Party Transaction [Line Items]
Entity Address, State or Province	Minnesota
Tilden [Member]
Related Party Transaction [Line Items]
Entity Address, State or Province	Michigan
Empire [Member]
Related Party Transaction [Line Items]
Entity Address, State or Province	Michigan
Koolyanobbing [Member]
Related Party Transaction [Line Items]
Entity Address, State or Province	Western Australia