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Income and Social Contribution Taxes - Summary of Income and Social Contribution Taxes recoverable (Detail) - BRL (R$)
R$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Disclosure of income and social contribution taxes [Abstract]    
Income tax R$ 224 R$ 436
Social contribution tax 116 154
Income and social contribution tax credits current 340 590
Income tax 7 98
Social contribution tax 14 14
Income and social contribution tax credits noncurrent 21 112
Income and social contribution tax credits R$ 361 R$ 702