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IMPAIRMENT (Details 3) - Individual assets or cash-generating units [member]
$ in Millions
Dec. 31, 2018
USD ($)
$100 per ounce change in gold price [Member] | Rainy River Mines [Member]  
Impairment [Line Items]  
Recoverable Amount $ 256.6
$100 per ounce change in gold price [Member] | Blackwater Mines [Member]  
Impairment [Line Items]  
Recoverable Amount 0.0
0.5% change in discount rate [Member] | Rainy River Mines [Member]  
Impairment [Line Items]  
Recoverable Amount 24.7
0.5% change in discount rate [Member] | Blackwater Mines [Member]  
Impairment [Line Items]  
Recoverable Amount 0.0
5% change in foreign exchange rate [Member] | Rainy River Mines [Member]  
Impairment [Line Items]  
Recoverable Amount 103.4
5% change in foreign exchange rate [Member] | Blackwater Mines [Member]  
Impairment [Line Items]  
Recoverable Amount 0.0
5% change in operating costs [Member] | Rainy River Mines [Member]  
Impairment [Line Items]  
Recoverable Amount 106.6
5% change in operating costs [Member] | Blackwater Mines [Member]  
Impairment [Line Items]  
Recoverable Amount 0.0
5% change in in-situ ounces [Member] | Rainy River Mines [Member]  
Impairment [Line Items]  
Recoverable Amount 10.9
5% change in in-situ ounces [Member] | Blackwater Mines [Member]  
Impairment [Line Items]  
Recoverable Amount $ 16.4