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Revenue - Summary of Changes in Contract Assets and Contract Liabilities (Detail) - TWD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Contract assets      
Net increase of customer contracts $ 6,035 $ 5,972 $ 6,066
Reclassified to trade receivables (6,039) (5,681) (6,405)
Significant changes of contract assets (4) 291 (339)
Contract liabilities      
Net increase of customer contracts 0 7 22
Recognized as revenues (12) (30) (89)
Significant changes of contract liabilities $ (12) $ (23) $ (67)