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Post-Employment Obligation - Disclosure of Defined Benefit Plans Expense Recognised in Income Statement (Detail) - BRL (R$)
R$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure of fair value of plan assets [line items]      
Cost of current service R$ 15 R$ 19 R$ 17
Interest on the actuarial obligation 1,161 1,246 1,263
Expected return on the assets of the Plan (771) (810) (833)
Past service cost   (619)  
Expense according to actuarial calculation 405 (164) 447
Pension plans and retirement supplement plans [member]      
Disclosure of fair value of plan assets [line items]      
Cost of current service 4 5 5
Interest on the actuarial obligation 959 980 1,014
Expected return on the assets of the Plan (771) (810) (833)
Expense according to actuarial calculation 192 175 186
Health plan [member]      
Disclosure of fair value of plan assets [line items]      
Cost of current service 10 11 9
Interest on the actuarial obligation 172 178 173
Expense according to actuarial calculation 182 189 182
Dental plan [member]      
Disclosure of fair value of plan assets [line items]      
Cost of current service 0    
Interest on the actuarial obligation 4 3 4
Expense according to actuarial calculation 4 3 4
Life insurance [member]      
Disclosure of fair value of plan assets [line items]      
Cost of current service 1 3 3
Interest on the actuarial obligation 26 85 72
Past service cost   (619)  
Expense according to actuarial calculation R$ 27 R$ (531) R$ 75