XML 163 R147.htm IDEA: XBRL DOCUMENT v3.21.1
Hedging Financial Instruments - Summary of Hedging Instrument (Details) - Forecast Purchases - forward Exchange Contract [Member] - Cash flow hedges [member]
€ in Millions, $ in Millions
 12 Months Ended
Dec. 31, 2020
TWD ($)
Dec. 31, 2019
TWD ($)
Dec. 31, 2018
TWD ($)
Dec. 31, 2020
EUR (€)
Dec. 31, 2019
EUR (€)
Dec. 31, 2018
EUR (€)
Disclosure Of Detailed Information About Hedging Instruments [Line Items]            
Change in Value of Hedged Item Used for Calculating Hedge Ineffectiveness $ (2) $ 1 $ (2)      
Accumulated Gain or Loss on Hedging Instruments in Other Equity Continuing Hedges 2 0 1      
Accumulated Gain or Loss on Hedging Instruments in Other Equity Hedge Accounting No Longer Applied $ 0 $ 0 $ 0      
Foreign currency risk [Member]            
Disclosure Of Detailed Information About Hedging Instruments [Line Items]            
Currency NT$/EUR NT$/EUR NT$/EUR      
Contract Amount $ 201 $ 84 $ 172 € 6 € 2 € 5
Maturity Period 2021.03 2020.03 2019.03      
Forward Rate 34.45 33.66 34.98      
Carrying Amount of Asset $ 2 $ 0 $ 1      
Carrying Amount of Liability 0 0 0      
Change in Fair Values of Hedging Instruments Used for Calculating Hedge Ineffectiveness $ 2 $ (1) $ 2