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Equity - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2020 shares	Dec. 31, 2019 shares
Disclosure of classes of share capital [line items]
Number of shares represented by each ADS	2
Percentage of legal reserve on share capital	25.00%
Shares held by subsidiaries	72,941,000	72,941,000
American depository shares (ADs) [member]
Disclosure of classes of share capital [line items]
Number of shares represented by each ADS	2
Number of shares outstanding	107,964,000	125,542,000
Ordinary shares [member]
Disclosure of classes of share capital [line items]
Number of shares outstanding	215,927,000	251,084,000
Top of range [member]
Disclosure of classes of share capital [line items]
Percentage of cash dividend on dividend distribution	30.00%

X

- Definition

Cash dividend percentage on dividend distribution.

+ References

No definition available.

+ Details

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Namespace Prefix:	asx_
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Balance Type:	na
Period Type:	duration

X

- Definition

Number of ordinary shares per ADS.

+ References

No definition available.

+ Details

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X

- Definition

Percentage of legal reserve on share capital.

+ References

No definition available.

+ Details

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Balance Type:	na
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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.

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X

- Definition

The number of shares that have been authorised and issued, reduced by treasury shares held. [Refer: Treasury shares]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2020-01-01
-Paragraph 79
-Subparagraph a
-Clause iv
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_79_a_iv&doctype=Standard
-URIDate 2020-01-01

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Period Type:	instant

X

- Definition

The number of shares in the entity held by the entity or by its subsidiaries or associates. [Refer: Associates [member]; Subsidiaries [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2020-01-01
-Paragraph 79
-Subparagraph a
-Clause vi
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_79_a_vi&doctype=Standard
-URIDate 2020-01-01

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X

- Details

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- Details

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- Details

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