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Employee Defined Benefit Obligations - Summary of Principal Assumptions Used In Determining Pension Benefit Obligations (Detail)
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Disclosure of defined benefit plans [line items]    
Discount rate 2.77% 2.47%
Rate of increase in salaries 4.47% 3.51%
Rate of inflation, pre-retirement 2.55% 2.40%
Rate of increase in future pensions payment 3.51% 3.53%
Life expectancy at age 65 for current pensioners:    
Male 22 years 22 years
Female 24 years 24 years
Life expectancy at age 65 for current members aged 40 or 45:    
Male 23 years 23 years
Female 25 years 26 years