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Employees - Summary of Assumptions, Weighted by Liabilities for Valuation of Defined Benefit Plans Which cover Approximately 96% of Total Pension Plan (Detail)
Dec. 31, 2018
Dec. 31, 2017
Defined benefit pension plans [Member]    
Disclosure of defined benefit plans [line items]    
Discount rate 2.70% 2.50%
Inflation 2.50% 2.50%
Rate of increase in salaries 2.80% 2.80%
Rate of increase for pensions in payment (where provided) 2.40% 2.40%
Rate of increase for pensions in deferment (where provided) 2.60% 2.60%
Other Post-Employment Benefit Plans [Member]    
Disclosure of defined benefit plans [line items]    
Discount rate 4.80% 4.20%
Rate of increase in salaries 3.00% 3.00%
Long-term medical cost inflation 5.30% 5.30%