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Operating Costs And Expenses - Summary of Operating Provisions (Reversals) (Detail) - BRL (R$)
R$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure Of Operating Provisions Reversals [Line Items]      
Estimated losses on doubtful receivables R$ 248 R$ 382 R$ 175
Estimated losses on other accounts receivables 27 40  
Contingency provisions (reversals) 0 0 0
Labor claims 206 120 4
Civil 27 30 22
Tax 7 2 (4)
Environmental     (1)
Regulatory (3)   10
Other (6) 31 (3)
Other provisions 231 183 28
Adjustment for losses      
Provision for losses 854 704 1,401
Put option [Member] | Parati [member]      
Adjustment for losses      
Provision for losses 231 55 1,079
Put option [Member] | SAAG [Member]      
Adjustment for losses      
Provision for losses 116 49 R$ 119
Put option [Member] | Sonda [Member]      
Adjustment for losses      
Provision for losses R$ 1 R$ (5)