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Assets Pledged as Collateral or for Security - Additional Information (Detail)	12 Months Ended
	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%

X

- Definition

Proportion of ownership interest in subsidiary pledged as collateral.

+ References

No definition available.

+ Details

Name:	asx_ProportionOfOwnershipInterestInSubsidiaryPledgedAsCollateral
Namespace Prefix:	asx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- 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

Name:	ifrs-full_DisclosureOfBusinessCombinationsLineItems
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

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

X

- Details

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