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