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Environmental And Mine Closure Obligations (Asset Retirement Obligation Disclosure) (Details) (USD $)
In Millions
9 Months Ended12 Months Ended
Sep. 30, 2011
Dec. 31, 2010
Environmental And Mine Closure Obligations [Abstract]  
Asset retirement obligation at beginning of period$ 168.3[1]$ 103.9[1]
Accretion expense11.813.1[1]
Exchange rate changes(1.1)2.5[1]
Revision in estimated cash flows 1.0[1]
Payments(0.7)(8.4)[1]
Acquired through business combinations14.056.2[1]
Asset retirement obligation at end of period$ 192.3$ 168.3[1]
[1]Represents a 12-month rollforward of our asset retirement obligation at December 31, 2010.