This item represents an other than temporary decline in value that has been recognized against an investment accounted for under the equity method of accounting. The excess of the carrying amount over the fair value of the investment represents the amount of the write down which is or was reflected in earnings. The written down value is a new cost basis with the adjusted value of the investment becoming its new carrying value subject to the equity accounting method. Evidence of a loss in value might include, but would not necessarily be limited to, absence of an ability to recover the carrying amount of the investment or inability of the investee to sustain an earnings capacity which would justify the carrying amount of the investment.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES (Investments In Unconsolidated Ventures) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 27, 2012	Dec. 31, 2011
Schedule of Equity Method Investments [Line Items]
Investment	$ 108.4		$ 504.8
Amapa [Member] \| Investments In Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Interest Percentage		30.00%
Total percentage of Amapa sold	100.00%
Investment	101.9		498.6
Impairment of equity method investment	365.4
Cockatoo [Member] \| Other Liabilities [Member]
Schedule of Equity Method Investments [Line Items]
Interest Percentage	50.00%
Investment	(25.3)		(15.0)
Hibbing [Member] \| Other Liabilities [Member]
Schedule of Equity Method Investments [Line Items]
Investment	(2.1)		(6.8)
Other Equity Investees [Member] \| Investments In Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Investment	$ 33.9		$ 28.0
Hibbing [Member] \| Hibbing [Member] \| Investments In Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Interest Percentage	23.00%
Latin American Iron Ore [Member] \| Amapa [Member]
Schedule of Equity Method Investments [Line Items]
Interest Percentage	30.00%