RELATED PARTIES (Summary Of Other Ownership Interests) (Details)	Dec. 31, 2012
Empire [Member]
Related Party Transaction [Line Items]
Ownership Interest	79.00%
Tilden [Member]
Related Party Transaction [Line Items]
Ownership Interest	85.00%
Bloom Lake [Member]
Related Party Transaction [Line Items]
Ownership Interest	75.00%
Arcelor Mittal [Member] | Empire [Member]
Related Party Transaction [Line Items]
Ownership Interest	21.00%
Arcelor Mittal [Member] | Tilden [Member]
Related Party Transaction [Line Items]
Ownership Interest	0.00%
Arcelor Mittal [Member] | Hibbing [Member]
Related Party Transaction [Line Items]
Ownership Interest	62.30%
Arcelor Mittal [Member] | Bloom Lake [Member]
Related Party Transaction [Line Items]
Ownership Interest	0.00%
U. S. Steel Canada [Member] | Empire [Member]
Related Party Transaction [Line Items]
Ownership Interest	0.00%
U. S. Steel Canada [Member] | Tilden [Member]
Related Party Transaction [Line Items]
Ownership Interest	15.00%
U. S. Steel Canada [Member] | Hibbing [Member]
Related Party Transaction [Line Items]
Ownership Interest	14.70%
U. S. Steel Canada [Member] | Bloom Lake [Member]
Related Party Transaction [Line Items]
Ownership Interest	0.00%
WISCO [Member] | Empire [Member]
Related Party Transaction [Line Items]
Ownership Interest	0.00%
WISCO [Member] | Tilden [Member]
Related Party Transaction [Line Items]
Ownership Interest	0.00%
WISCO [Member] | Hibbing [Member]
Related Party Transaction [Line Items]
Ownership Interest	0.00%
WISCO [Member] | Bloom Lake [Member]
Related Party Transaction [Line Items]
Ownership Interest	25.00%
Equity Method Investments [Member] | Hibbing [Member] | Hibbing [Member]
Related Party Transaction [Line Items]
Ownership interest, equity method investment	23.00%