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Share-based Payment Arrangements - Summary of Information About ASE Inc. Option Plans (Detail) - The Company Option Plans [member]
shares in Thousands
 12 Months Ended
Dec. 31, 2021
shares
$ / shares
Dec. 31, 2020
shares
$ / shares
Dec. 31, 2019
shares
$ / shares
Disclosure of terms and conditions of share-based payment arrangement [Line Items]      
Number of options, beginning balance | shares 144,767 170,786 183,814
Number of options, forfeited | shares (5,907) (3,949) (4,214)
Number of options, expired | shares 0 (1,006)  
Number of options, exercised | shares (42,058) (21,064) (8,814)
Number of options, Ending balance | shares 96,802 144,767 170,786
Number of options, exercisable, end of year | shares 49,696 67,388 33,822
Weighted average exercise price, Beginning balance | $ / shares $ 56.9 $ 57.0 $ 58.1
Weighted average exercise price, Options expired | $ / shares 0 40.8  
Weighted average exercise price, Options forfeited | $ / shares 52.3 58.0 61.8
Weighted average exercise price, Options exercised | $ / shares 61.4 49.2 48.4
Weighted average exercise price, Ending balance | $ / shares 53.3 56.9 57.0
Weighted average exercise price, Options exercisable, end of year | $ / shares $ 55.5 $ 61.4 $ 63.5