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Intangible Assets - Summary of Composition of Intangible Assets (Detail) - BRL (R$)
R$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure of detailed information about intangible assets [line items]        
Intangible assets R$ 10,777 R$ 11,156 R$ 10,820 R$ 10,275
Temporary Easements Intangible Assets [member]        
Disclosure of detailed information about intangible assets [line items]        
Intangible assets 8 10    
Onerous concession [member]        
Disclosure of detailed information about intangible assets [line items]        
Intangible assets 7 8 9 9
Assets of Concession [member]        
Disclosure of detailed information about intangible assets [line items]        
Intangible assets 10,680 10,435 9,248 8,967
Others [member]        
Disclosure of detailed information about intangible assets [line items]        
Intangible assets 19 17    
Useful life defined intangible asset [member]        
Disclosure of detailed information about intangible assets [line items]        
Intangible assets 10,714 10,470 R$ 9,285 R$ 9,000
Intangible assets in progress [member]        
Disclosure of detailed information about intangible assets [line items]        
Intangible assets 63 686    
Gross Carrying Amount [member]        
Disclosure of detailed information about intangible assets [line items]        
Intangible assets 18,852 18,636    
Gross Carrying Amount [member] | Temporary Easements Intangible Assets [member]        
Disclosure of detailed information about intangible assets [line items]        
Intangible assets 11 12    
Gross Carrying Amount [member] | Onerous concession [member]        
Disclosure of detailed information about intangible assets [line items]        
Intangible assets 19 19    
Gross Carrying Amount [member] | Assets of Concession [member]        
Disclosure of detailed information about intangible assets [line items]        
Intangible assets 18,674 17,837    
Gross Carrying Amount [member] | Others [member]        
Disclosure of detailed information about intangible assets [line items]        
Intangible assets 85 82    
Gross Carrying Amount [member] | Useful life defined intangible asset [member]        
Disclosure of detailed information about intangible assets [line items]        
Intangible assets 18,789 17,950    
Gross Carrying Amount [member] | Intangible assets in progress [member]        
Disclosure of detailed information about intangible assets [line items]        
Intangible assets 63 686    
Accumulated amortization [member]        
Disclosure of detailed information about intangible assets [line items]        
Intangible assets (8,075) (7,480)    
Accumulated amortization [member] | Temporary Easements Intangible Assets [member]        
Disclosure of detailed information about intangible assets [line items]        
Intangible assets (3) (2)    
Accumulated amortization [member] | Onerous concession [member]        
Disclosure of detailed information about intangible assets [line items]        
Intangible assets (12) (11)    
Accumulated amortization [member] | Assets of Concession [member]        
Disclosure of detailed information about intangible assets [line items]        
Intangible assets (7,994) (7,402)    
Accumulated amortization [member] | Others [member]        
Disclosure of detailed information about intangible assets [line items]        
Intangible assets (66) (65)    
Accumulated amortization [member] | Useful life defined intangible asset [member]        
Disclosure of detailed information about intangible assets [line items]        
Intangible assets R$ (8,075) R$ (7,480)