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Retirement Benefit Plans - Amounts Included in Consolidated Balance Sheets from Obligation in Respect of Defined Benefit Plans (Detail)
$ in Millions, $ in Millions
Dec. 31, 2018
TWD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
TWD ($)
Dec. 31, 2016
TWD ($)
Dec. 31, 2015
TWD ($)
Disclosure Of Defined Benefit Plans [Abstract]          
Present value of funded defined benefit obligation $ 41,397   $ 37,663    
Fair value of plan assets (39,027)   (34,972)    
Funded status - deficit 2,370   2,691    
Net defined benefit liabilities 3,534 $ 115 2,704    
Net defined benefit assets (1,164) $ (38) (13)    
Defined benefit obligation $ 2,370   $ 2,691 $ 618 $ 7,088