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, 2017
Dec. 31, 2016
Asset Retirement Obligation [Roll Forward]    
Asset retirement obligation at beginning of period $ 204.0 $ 230.4
Accretion expense 7.1 14.0
Asset Retirement Obligation, Liabilities Settled (0.8) (2.2)
Exchange rate changes 1.0 (0.2)
Revision in estimated cash flows   (38.0)
Asset retirement obligation at end of period $ 211.3 $ 204.0