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Employee Benefits - Summary of Weighted Average Assumptions Used to Determine Pension Benefits of Defined Benefit Pension Plans (Detail)
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure Of Defined Benefit Plans [Line Items]      
Rate of increase in compensation 6.00% 6.00% 6.00%
Discount rate 7.30% 5.80% 5.30%
Investment property [member] | Smart and Subsidiaries [Member]      
Disclosure Of Defined Benefit Plans [Line Items]      
Rate of increase in compensation 7.30% 5.00% 5.00%
Discount rate 6.00% 5.80% 5.20%