EMPLOYEE BENEFITS - Post-employment health care benefit plan - Sensitivity Analysis (Details) - Post-employment health care benefit - Discount rate R$ in Thousands	Dec. 31, 2017 BRL (R$)
Sensitivity analysis
Increase in actuarial assumption (as a percent)	1.00%
Decrease in actuarial assumption (as a percent)	1.00%
Total service costs and interest costs
Sensitivity analysis
Increase (decrease) in defined benefit obligation due to increase in actuarial assumption	R$ 92
Increase (decrease) in defined benefit obligation due to decrease in actuarial assumption	(765)
Present value of the defined benefit obligations
Sensitivity analysis
Increase (decrease) in defined benefit obligation due to increase in actuarial assumption	37,871
Increase (decrease) in defined benefit obligation due to decrease in actuarial assumption	R$ (47,434)

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- Definition

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]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2017-01-01
-Paragraph 145
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- Definition

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]]

+ References

+ Details

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- Definition

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

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