Quarterly report pursuant to Section 13 or 15(d)

Related Parties (Summary Of Other Ownership Interests) (Detail)

v2.4.0.6
Related Parties (Summary Of Other Ownership Interests) (Detail)
Sep. 30, 2012
Sep. 30, 2011
Empire [Member]
   
Related Party Transaction [Line Items]    
Ownership interest, percent 79.00% 79.00%
Tilden [Member]
   
Related Party Transaction [Line Items]    
Ownership interest, percent 85.00% 85.00%
Bloom Lake [Member]
   
Related Party Transaction [Line Items]    
Ownership interest, percent 75.00% 75.00%
Cliffs Natural Resources [Member] | Empire [Member]
   
Related Party Transaction [Line Items]    
Ownership interest, percent 79.00%  
Cliffs Natural Resources [Member] | Tilden [Member]
   
Related Party Transaction [Line Items]    
Ownership interest, percent 85.00%  
Cliffs Natural Resources [Member] | Bloom Lake [Member]
   
Related Party Transaction [Line Items]    
Ownership interest, percent 75.00%  
Arcelor Mittal [Member] | Empire [Member]
   
Related Party Transaction [Line Items]    
Ownership interest, percent 21.00%  
Arcelor Mittal [Member] | Tilden [Member]
   
Related Party Transaction [Line Items]    
Ownership interest, percent 0.00%  
Arcelor Mittal [Member] | Hibbing [Member]
   
Related Party Transaction [Line Items]    
Ownership interest, percent 62.30%  
Arcelor Mittal [Member] | Bloom Lake [Member]
   
Related Party Transaction [Line Items]    
Ownership interest, percent 0.00%  
U. S. Steel Canada [Member] | Empire [Member]
   
Related Party Transaction [Line Items]    
Ownership interest, percent 0.00%  
U. S. Steel Canada [Member] | Tilden [Member]
   
Related Party Transaction [Line Items]    
Ownership interest, percent 15.00%  
U. S. Steel Canada [Member] | Hibbing [Member]
   
Related Party Transaction [Line Items]    
Ownership interest, percent 14.70%  
U. S. Steel Canada [Member] | Bloom Lake [Member]
   
Related Party Transaction [Line Items]    
Ownership interest, percent 0.00%  
WISCO [Member] | Empire [Member]
   
Related Party Transaction [Line Items]    
Ownership interest, percent 0.00%  
WISCO [Member] | Tilden [Member]
   
Related Party Transaction [Line Items]    
Ownership interest, percent 0.00%  
WISCO [Member] | Hibbing [Member]
   
Related Party Transaction [Line Items]    
Ownership interest, percent 0.00%  
WISCO [Member] | Bloom Lake [Member]
   
Related Party Transaction [Line Items]    
Ownership interest, percent 25.00%  
Other Liabilities [Member] | Hibbing [Member] | Cliffs Natural Resources [Member]
   
Related Party Transaction [Line Items]    
Equity Method Investment, Ownership Percentage 23.00%