Segment Reporting (Schedule Of Summary Of Assets, By Segment) (Details) (USD $) In Millions |
Sep. 30, 2011 |
Dec. 31, 2010 |
|---|---|---|
| Total assets | $ 13,945.3 | $ 7,778.2 |
U.S. Iron Ore [Member] |
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| Total assets | 1,772.2 | 1,537.1 |
Eastern Canadian Iron Ore [Member] |
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| Total assets | 7,712.6 | 629.6 |
North American Coal [Member] |
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| Total assets | 1,718.9 | 1,623.8 |
Asia Pacific Iron Ore [Member] |
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| Total assets | 1,343.1 | 1,195.3 |
Other Segment [Member] |
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| Total assets | 1,165.6 | 1,257.8 |
Total Segment Assets [Member] |
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| Total assets | 13,712.4 | 6,243.6 |
Corporate [Member] |
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| Total assets | $ 232.9 | $ 1,534.6 |
| X | ||||||||||
- Definition Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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