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Retirement Benefit Plans - Principal Assumptions Used for Actuarial Valuations (Detail)
Dec. 31, 2019
Dec. 31, 2018
Disclosure Of Defined Plan [line items]    
Discount rates 0.75% 1.00%
Bottom of range [Member]    
Disclosure Of Defined Plan [line items]    
Expected rates of salary increase 1.20% 1.20%
Top of range [Member]    
Disclosure Of Defined Plan [line items]    
Expected rates of salary increase 2.00% 2.00%