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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, 2020
TWD ($)
Dec. 31, 2020
USD ($)
Dec. 31, 2019
TWD ($)
Disclosure of defined benefit plans [abstract]      
Present value of defined benefit obligation $ 16,980.3   $ 13,484.1
Fair value of plan assets (5,066.2)   (4,301.6)
Net defined benefit liability $ 11,914.1 $ 424.3 $ 9,182.5