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Revenues - Summary of Other Operating Revenues (Detail) - BRL (R$)
R$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure of revenue [Line Items]      
Other revenue R$ 1,484 R$ 1,421 R$ 1,440
Charged service [Member]      
Disclosure of revenue [Line Items]      
Other revenue 10 6 14
Telecoms services [Member]      
Disclosure of revenue [Line Items]      
Other revenue 149 137 134
Services rendered [Member]      
Disclosure of revenue [Line Items]      
Other revenue 156 167 131
Subsidies [Member]      
Disclosure of revenue [Line Items]      
Other revenue 1,034 1,001 996
Rental and leasing [Member]      
Disclosure of revenue [Line Items]      
Other revenue 121 105 93
Other [Member]      
Disclosure of revenue [Line Items]      
Other revenue R$ 14 R$ 5 R$ 72