Related Parties (Summary Of Other Ownership Interests) (Details)	Mar. 31, 2012	Mar. 31, 2011
Empire [Member]
Related Party Transaction [Line Items]
Ownership Interest	79.00%	79.00%
Tilden [Member]
Related Party Transaction [Line Items]
Ownership Interest	85.00%	85.00%
Bloom Lake [Member]
Related Party Transaction [Line Items]
Ownership Interest	75.00%	75.00%
Cliffs Natural Resources [Member] | Empire [Member]
Related Party Transaction [Line Items]
Ownership Interest	79.00%
Cliffs Natural Resources [Member] | Tilden [Member]
Related Party Transaction [Line Items]
Ownership Interest	85.00%
Cliffs Natural Resources [Member] | Hibbing [Member]
Related Party Transaction [Line Items]
Ownership Interest	23.00%
Cliffs Natural Resources [Member] | 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] | Hibbing [Member]
Related Party Transaction [Line Items]
Ownership Interest	62.30%
U. S. Steel Canada | Tilden [Member]
Related Party Transaction [Line Items]
Ownership Interest	15.00%
U. S. Steel Canada | Hibbing [Member]
Related Party Transaction [Line Items]
Ownership Interest	14.70%
WISCO [Member] | Bloom Lake [Member]
Related Party Transaction [Line Items]
Ownership Interest	25.00%