BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Schedule Of Subsidiaries) (Details)	3 Months Ended
	Mar. 31, 2019
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
Metallics [Member]
Related Party Transaction [Line Items]
Entity Address, State or Province	Ohio