XML 161 R80.htm IDEA: XBRL DOCUMENT v3.20.4
SIGNIFICANT ACCOUNTING POLICIES - Estimated Useful Lives of Major Asset Categories (Details)
 12 Months Ended
Dec. 31, 2020
Minimum | Buildings, plant and equipment1  
Disclosure of detailed information about property, plant and equipment [line items]  
Useful life measured as period of time, property, plant and equipment 1 year
Minimum | Underground mobile equipment  
Disclosure of detailed information about property, plant and equipment [line items]  
Useful life measured as period of time, property, plant and equipment 3 years
Minimum | Light vehicles and other mobile equipment  
Disclosure of detailed information about property, plant and equipment [line items]  
Useful life measured as period of time, property, plant and equipment 1 year
Minimum | Furniture, computer and office equipment  
Disclosure of detailed information about property, plant and equipment [line items]  
Useful life measured as period of time, property, plant and equipment 1 year
Maximum | Buildings, plant and equipment1  
Disclosure of detailed information about property, plant and equipment [line items]  
Useful life measured as period of time, property, plant and equipment 34 years
Maximum | Underground mobile equipment  
Disclosure of detailed information about property, plant and equipment [line items]  
Useful life measured as period of time, property, plant and equipment 7 years
Maximum | Light vehicles and other mobile equipment  
Disclosure of detailed information about property, plant and equipment [line items]  
Useful life measured as period of time, property, plant and equipment 7 years
Maximum | Furniture, computer and office equipment  
Disclosure of detailed information about property, plant and equipment [line items]  
Useful life measured as period of time, property, plant and equipment 7 years