BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Schedule Of Subsidiaries) (Details)	6 Months Ended
	Jun. 30, 2018
Northshore
Related Party Transaction [Line Items]
Entity Address, State or Province	Minnesota
United Taconite
Related Party Transaction [Line Items]
Entity Address, State or Province	Minnesota
Tilden
Related Party Transaction [Line Items]
Entity Address, State or Province	Michigan
Empire
Related Party Transaction [Line Items]
Entity Address, State or Province	Michigan
Koolyanobbing
Related Party Transaction [Line Items]
Entity Address, State or Province	Western Australia