Annual report pursuant to Section 13 and 15(d)

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

v3.10.0.1
BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Schedule Of Subsidiaries) (Details)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Related Party Transaction [Line Items]    
Noncontrolling Interest, Ownership Percentage by Parent 100.00%  
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  
Noncontrolling Interest, Ownership Percentage by Parent   100.00%
Empire [Member]    
Related Party Transaction [Line Items]    
Entity Address, State or Province Michigan  
Noncontrolling Interest, Ownership Percentage by Parent   100.00%