Quarterly report pursuant to Section 13 or 15(d)

Environmental and Mine Closure Obligations (Asset Retirement Obligation Disclosure) (Details)

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Environmental and Mine Closure Obligations (Asset Retirement Obligation Disclosure) (Details) (USD $)
In Millions
6 Months Ended 12 Months Ended
Jun. 30, 2011
Dec. 31, 2010
Environmental and Mine Closure Obligations    
Asset retirement obligation at beginning of period $ 168.3 [1] $ 103.9 [1]
Accretion expense 7.7 13.1 [1]
Exchange rate changes 1.2 2.5 [1]
Revision in estimated cash flows   1.0 [1]
Payments (0.7) (8.4) [1]
Acquired through business combinations 14.0 56.2 [1]
Asset retirement obligation at end of period $ 190.5 $ 168.3 [1]
[1] Represents a 12-month rollforward of our asset retirement obligation at December 31, 2010.