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Retirement Benefit Plans - Pension Costs Recognized in Profit and Loss for Defined Benefit Plans (Detail) - TWD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Disclosure Of Defined Plan [line items]      
Defined benefit plans pension costs recognized in profit and loss $ 1,216 $ 2,001 $ 2,859
Operating costs [Member]      
Disclosure Of Defined Plan [line items]      
Defined benefit plans pension costs recognized in profit and loss 725 1,205 1,726
Marketing expenses [Member]      
Disclosure Of Defined Plan [line items]      
Defined benefit plans pension costs recognized in profit and loss 367 603 866
General and administrative expenses [Member]      
Disclosure Of Defined Plan [line items]      
Defined benefit plans pension costs recognized in profit and loss 80 121 164
Research and development expenses [Member]      
Disclosure Of Defined Plan [line items]      
Defined benefit plans pension costs recognized in profit and loss $ 44 $ 72 $ 103