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8. RECEIVABLES FROM CUSTOMERS, TRADERS AND POWER TRANSPORT CONCESSION HOLDERS (Details 2) - BRL (R$)
R$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Cemig GT [member]      
Disclosure Of Advances From Customers [line items]      
Beginning balance R$ 810 R$ 751 R$ 568
Effect of adoption of IFRS 9 on Jan. 1, 2018     150
Additions 146   264
Write-off     (231)
Disposals (244)    
Ending Balance 712 810 751
Eletrobras [member]      
Disclosure Of Advances From Customers [line items]      
Beginning balance R$ 810 751  
Additions   238  
Disposals   (179)  
Ending Balance   R$ 810 R$ 751