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v3.22.1

Assets Pledged as Collateral or for Security - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2020
FAFG [Member] | Syndicated bank loans [Member] |
Disclosure of detailed information about business combination [line items] |
Proportion of Ownership Interest in Subsidiary Pledged as Collateral | 89.60%

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- Definition Proportion of ownership interest in subsidiary pledged as collateral. + References No definition available. + Details
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Namespace Prefix: | asx_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with members defined in one or many axes of the table. + References No definition available. + Details
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Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | ifrs-full_BusinessCombinationsAxis=asx_FinanciereafgsasMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | ifrs-full_ClassesOfFinancialLiabilitiesAxis=asx_SyndicatedBankLoansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |