Quarterly report pursuant to Section 13 or 15(d)

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Schedule Of Subsidiaries) (Details)

v3.19.1
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