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17. PROPERTY, PLANT AND EQUIPMENT (Details 3)
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Disclosure of detailed information about property, plant and equipment [line items]      
Average annual depreciation rate 3.14% 3.13% 3.72%
Hydroelectric generation [member]      
Disclosure of detailed information about property, plant and equipment [line items]      
Average annual depreciation rate 2.96%    
Wind power generation [member]      
Disclosure of detailed information about property, plant and equipment [line items]      
Average annual depreciation rate 4.94%    
Administration [member]      
Disclosure of detailed information about property, plant and equipment [line items]      
Average annual depreciation rate 6.19%