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Retirement Benefit Plans - Amounts Arising from Defined Benefit Obligation in Consolidated Statements of Financial Position (Detail)
$ in Millions, $ in Millions
Dec. 31, 2019
TWD ($)
Dec. 31, 2019
USD ($)
Dec. 31, 2018
TWD ($)
Disclosure of defined benefit plans [abstract]      
Present value of defined benefit obligation $ 13,484.1   $ 13,662.7
Fair value of plan assets (4,301.6)   (4,011.3)
Net defined benefit liability $ 9,182.5 $ 307.0 $ 9,651.4