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Post-Employment Benefits - Summary of Changes in Net Amount Recognized in Balance Sheet (Parenthetical) (Detail) - BRL (R$)
R$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure of defined benefit plans [abstract]      
Discount rate 9.72% 9.98% 10.24%
Actual return on assets R$ 2,266 R$ 2,124