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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, 2018
TWD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
TWD ($)
Disclosure of defined benefit plans [abstract]      
Present value of defined benefit obligation $ 13,662.7   $ 12,774.6
Fair value of plan assets (4,011.3)   (3,923.9)
Net defined benefit liability $ 9,651.4 $ 315.3 $ 8,850.7