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v3.20.1

Investment Properties - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2019
Bottom of range [member] |
Disclosure of detailed information about investment property [line items] |
Operating lease Term | 1 year
Top of range [member] |
Disclosure of detailed information about investment property [line items] |
Operating lease Term | 15 years

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- Definition Operating lease Term + References No definition available. + Details
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Namespace Prefix: | asx_
Data Type: | xbrli:durationItemType
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 domain 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_RangeAxis=ifrs-full_BottomOfRangeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_RangeAxis=ifrs-full_TopOfRangeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |