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Intangible Assets - Summary of Changes in Intangible Assets (Detail) - BRL (R$)
R$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure of detailed information about intangible assets [line items]      
Beginning balance R$ 11,156 R$ 10,820 R$ 10,275
Assets arising from business combination 166    
Additions 34 1,105 1,163
Special obligations write-down     98
Disposals (27) (19) (40)
Effects of first-time adoption of IFRS 15 (621)    
Amortization (675) (646) (599)
Transfer to Held for sale (7)    
Transfer 751 (104) (77)
Ending balance 10,777 11,156 10,820
Intangible assets in progress [member]      
Disclosure of detailed information about intangible assets [line items]      
Beginning balance 686 1,535 1,275
Additions 33 1,105 1,157
Disposals (4) (8) (8)
Effects of first-time adoption of IFRS 15 (621)    
Transfer (31) (1,946) (889)
Ending balance 63 686 1,535
Temporary Easements [member]      
Disclosure of detailed information about intangible assets [line items]      
Beginning balance 10 10 10
Amortization (1)    
Ending balance 9 10 10
Onerous concession [member]      
Disclosure of detailed information about intangible assets [line items]      
Beginning balance 8 9 9
Amortization (1) (1)  
Ending balance 7 8 9
Assets of Concession [member]      
Disclosure of detailed information about intangible assets [line items]      
Beginning balance 10,435 9,248 8,967
Assets arising from business combination 162    
Additions     6
Special obligations write-down     98
Disposals (23) (11) (32)
Amortization (668) (638) (595)
Transfer 774 1,836 804
Ending balance 10,680 10,435 9,248
Others [member]      
Disclosure of detailed information about intangible assets [line items]      
Beginning balance 17 18 14
Assets arising from business combination 4    
Additions 1    
Amortization (5) (7) (4)
Transfer to Held for sale (7)    
Transfer 8 6 8
Ending balance 18 17 18
Useful life defined intangible asset [member]      
Disclosure of detailed information about intangible assets [line items]      
Beginning balance 10,470 9,285 9,000
Assets arising from business combination 166    
Additions 1   6
Special obligations write-down     98
Disposals (23) (11) (32)
Amortization (675) (646) (599)
Transfer to Held for sale (7)    
Transfer 782 1,842 812
Ending balance R$ 10,714 R$ 10,470 R$ 9,285