Annual report pursuant to Section 13 and 15(d)

RELATED PARTIES (Summary Of Other Ownership Interests) (Details)

v3.8.0.1
RELATED PARTIES (Summary Of Other Ownership Interests) (Details)
Dec. 31, 2017
Related Party Transaction [Line Items]  
Noncontrolling Interest, Ownership Percentage by Parent 100.00%
Hibbing [Member] | Arcelor Mittal [Member]  
Related Party Transaction [Line Items]  
Ownership interest, equity method investment 62.30%
Hibbing [Member] | U. S. Steel Canada [Member]  
Related Party Transaction [Line Items]  
Ownership interest, equity method investment 14.70%
Empire [Member]  
Related Party Transaction [Line Items]  
Noncontrolling Interest, Ownership Percentage by Parent 100.00%
Tilden [Member]  
Related Party Transaction [Line Items]  
Noncontrolling Interest, Ownership Percentage by Parent 100.00%
Investments in Ventures [Member] | Hibbing [Member]  
Related Party Transaction [Line Items]  
Ownership interest, equity method investment 23.00%