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Investments - Allocation of Acquisition Price of Jointly-Controlled Subsidiaries, A Valuation was Made of Intangible Assets Relating to Right to Operate Regulated Activity (Detail) - BRL (R$)
R$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure of detailed information about investment property [line items]      
Beginning balance R$ 418 R$ 594 R$ 646
Additions 20   99
Amortization (36) (47) (42)
Written off (222) (129) (109)
Ending balance 180 418 594
Taesa [member]      
Disclosure of detailed information about investment property [line items]      
Beginning balance 189 288 415
Amortization (9) (13) (18)
Written off   (86) (109)
Ending balance 180 189 288
Light [member]      
Disclosure of detailed information about investment property [line items]      
Beginning balance 186 209 231
Amortization (22) (23) (22)
Written off (164)    
Ending balance   186 209
Lepsa [member]      
Disclosure of detailed information about investment property [line items]      
Beginning balance   49  
Additions     50
Amortization   (6) (1)
Written off   (43)  
Ending balance     49
RME [member]      
Disclosure of detailed information about investment property [line items]      
Beginning balance 43 48  
Additions 20   49
Amortization (5) (5) (1)
Written off R$ (58)    
Ending balance   R$ 43 R$ 48