Basis Of Presentation And Significant Accounting Policies (Investments In Unconsolidated Ventures) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Schedule of Equity Method Investments [Line Items]
Investment	$ 512.6	$ 504.8
Amapa [Member] | Investments In Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Interest Percentage	30.00%
Investment	492.5	498.6
AusQuest [Member] | Investments In Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Interest Percentage	30.00%
Investment	3.5	3.7
Cockatoo [Member] | Other Liabilities [Member]
Schedule of Equity Method Investments [Line Items]
Interest Percentage	50.00%
Investment	(13.9)	(15.0)
Hibbing [Member] | Other Liabilities [Member]
Schedule of Equity Method Investments [Line Items]
Interest Percentage	23.00%
Investment	(4.4)	(6.8)
Other Equity Investees [Member] | Investments In Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Investment	$ 34.9	$ 24.3