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Retirement Benefit Plans - Summary of Key Assumptions Used for the Actuarial Valuations (Detail)
Dec. 31, 2019
Dec. 31, 2018
Bottom of range [member]    
Disclosure of defined benefit plans [line items]    
Discount rates 0.08% 0.05%
Expected rates of salary increase 1.00% 1.75%
Top of range [member]    
Disclosure of defined benefit plans [line items]    
Discount rates 2.85% 3.02%
Expected rates of salary increase 4.01% 4.06%