Pensions and Other Post-Employment Benefits - Summary of Principal Weighted Average Actuarial Assumptions Used to Determine Benefit Obligations and Expenses (Detail) - yr	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Benefits [Member]
Disclosure Of Actuarial Assumptions [Line Items]
Discount Rate	3.50%	3.50%	3.75%
Future Salary Growth Rate	3.88%	3.81%	3.80%
Average Longevity (years)	88.2	88.0	87.9
OPEB [Member]
Disclosure Of Actuarial Assumptions [Line Items]
Discount Rate	3.50%	3.25%	3.75%
Future Salary Growth Rate	5.08%	5.08%	5.15%
Average Longevity (years)	88.1	88.0	87.9
Health Care Cost Trend Rate	6.00%	6.00%	7.00%

Disclosure of actuarial assumptions.

No definition available.

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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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- Definition

The expected rate of salary increases used as a significant actuarial assumption to determine the present value of a defined benefit obligation. [Refer: Defined benefit plans [member]; Defined benefit obligation, at present value; Actuarial assumptions [member]]

+ References

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- Definition

Medical cost trend rate used as significant actuarial assumption to determine the present value of a defined benefit obligation. [Refer: Defined benefit obligation, at present value; Actuarial assumptions [member]]

+ References

+ Details

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- Definition

The mortality rate used as a significant actuarial assumption to determine the present value of a defined benefit obligation. [Refer: Defined benefit obligation, at present value; Actuarial assumptions [member]]

+ References

+ Details

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- Details

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