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Fair Value Information - Schedule of Impact of Decrease in Discount for Lack of Marketability or Noncontrolling Interests (Detail) - TWD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Disclosure Of Fair Value Measurement Of Financial Instruments [Abstract]    
Discount for lack of marketability, 5% increase $ (32) $ (320)
Discount for lack of marketability, 5% decrease 32 320
Noncontrolling interests discount, 5% increase (19) (47)
Noncontrolling interests discount, 5% decrease 19 47
Long-term revenue growth rates, 0.1% increase 25 0
Long-term revenue growth rates, 0.1% decrease (25) 0
WACC, 1% increase (288) 0
WACC, 1% decrease $ 350 $ 0