Annual report pursuant to Section 13 and 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, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Asset Retirement Obligation [Roll Forward]    
Asset retirement obligation at beginning of period $ 194.9 $ 162.1
Accretion expense 17.6 15.7
Exchange rate changes 0.3 0.1
Revision in estimated cash flows 18.2 3.7
Payments 0.1 (0.7)
Acquired through business combinations    14.0
Asset retirement obligation at end of period $ 231.1 $ 194.9