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EMPLOYEE BENEFITS - Post-employment health care benefit plan - Sensitivity Analysis (Details) - Post-employment health care benefit - Discount rate R$ in Thousands	Dec. 31, 2018 BRL (R$)
Sensitivity analysis
Increase in actuarial assumption (as a percent)	1.00%
Decrease in actuarial assumption (as a percent)	1.00%
Total service costs and interest costs
Sensitivity analysis
Increase (decrease) in defined benefit obligation due to increase in actuarial assumption	R$ 2,051
Increase (decrease) in defined benefit obligation due to decrease in actuarial assumption	(1,612)
Present value of the defined benefit obligations
Sensitivity analysis
Increase (decrease) in defined benefit obligation due to increase in actuarial assumption	27,517
Increase (decrease) in defined benefit obligation due to decrease in actuarial assumption	R$ (22,743)

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The increase (decrease) in a defined benefit obligation that would have been caused by a decrease in a significant actuarial assumption that was reasonably possible at the end of the reporting period. [Refer: Actuarial assumptions [member]]

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The increase (decrease) in a defined benefit obligation that would have been caused by an increase in a significant actuarial assumption that was reasonably possible at the end of the reporting period. [Refer: Actuarial assumptions [member]]

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The reasonably possible percentage of the decrease in the actuarial assumption used to determine the present value of defined benefit obligation. [Refer: Actuarial assumptions [member]]

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