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Related Party Transactions - Additional Information (Detail) - BRL (R$)
R$ in Millions
 1 Months Ended
Sep. 18, 2019
Dec. 31, 2018
Nov. 30, 2018
Disclosure of transactions between related parties [line items]      
Loan settlement amount R$ 400    
Loan interest rate 125.52%    
Promissory note R$ 442    
Cemig GT [member]      
Disclosure of transactions between related parties [line items]      
Loan settlement amount     R$ 630
Loan interest rate     125.52%
Promissory note     R$ 639
Interest amount     R$ 9
Cemig D [member]      
Disclosure of transactions between related parties [line items]      
Loan settlement amount   R$ 630  
Loan interest rate   125.52%  
Promissory note   R$ 639  
Interest amount   R$ 9