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EMPLOYEE BENEFITS - Post-employment health care benefit plan - Assumptions (Details) - Post-employment health care benefit | Dec. 31, 2017 | Dec. 31, 2016
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Minimum |  |
Summary of assumptions used to calculate the defined benefit plans |  |
Average discount rate | 3.25% | 3.75%
Health treatment - rate assumed next year | 6.88% | 6.40%
Health treatment - Assumed rate of decline in the cost to achieve in the years of 2026 to 2041 | 4.00% | 4.00%
Maximum |  |
Summary of assumptions used to calculate the defined benefit plans |  |
Average discount rate | 3.50% | 4.25%
Health treatment - rate assumed next year | 7.60% | 6.80%
Health treatment - Assumed rate of decline in the cost to achieve in the years of 2026 to 2041 | 4.50% | 4.50%

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- Definition Medical cost trend rate for the next year after reporting period used as significant actuarial assumption to determine the present value of a defined benefit obligation. + References No definition available. + Details
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- Definition Medical cost trend rate of decline used as significant actuarial assumption to determine the present value of a defined benefit obligation. + References No definition available. + Details
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- References No definition available. + Details
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- Definition The discount rate used as the significant actuarial assumption to determine the present value of a defined benefit obligation. [Refer: Defined benefit obligation, at present value; Actuarial assumptions [member]] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 19 -IssueDate 2017-01-01 -Paragraph 144 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2017-03-01&anchor=para_144&doctype=Standard -URIDate 2017-03-09 + Details
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- Details
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