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Concession Contract Assets - Summary of Changes in Concession Contract Assets (Parenthetical) (Detail) - BRL (R$)
R$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure of assets recognised from costs to obtain or fulfil contracts with customers [line items]      
Additions to distribution asset R$ 893 R$ 25 R$ 2,271
Capitalised borrowing cost 26    
Provision for impairment 42    
Distribution [member]      
Disclosure of assets recognised from costs to obtain or fulfil contracts with customers [line items]      
Additions to distribution asset R$ 726