Retirement Benefit Plans - Effect on Present Value of Defined Benefit Obligation Due to a Reasonably Possible Change of the Significant Actuarial Assumptions (Parenthetical) (Detail)	Dec. 31, 2019	Dec. 31, 2018
Discount rates [Member]
Disclosure of sensitivity analysis for actuarial assumptions [Line Items]
Percentage increase in actuarial assumptions	0.50%	0.50%
Percentage decrease in actuarial assumptions	0.50%	0.50%
Expected rates of salary increases [Member]
Disclosure of sensitivity analysis for actuarial assumptions [Line Items]
Percentage increase in actuarial assumptions	0.50%	0.50%
Percentage decrease in actuarial assumptions	0.50%	0.50%