Contents of Significant Accounts - Operating Revenues - Additional Information (Detail) - TWD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Disclosure Of Additional Information About Revenue [Abstract]
Revenue that was included in contract liability balance at beginning of period	$ 706	$ 616
Transaction price allocated to unsatisfied performance obligations	2,759	2,987
Asset recognized from the cost to fulfill a contract with customer	$ 549	$ 560

The amount of assets recognised from the costs to obtain or fulfil contracts with customers. The costs to obtain a contract with a customer are the incremental costs of obtaining the contract that the entity would not have incurred if the contract had not been obtained. The costs to fulfil a contract with a customer are the costs that relate directly to a contract or to an anticipated contract that the entity can specifically identify.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 15
-IssueDate 2020-01-01
-Paragraph 128
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=15&code=ifrs-tx-2020-en-r&anchor=para_128_a&doctype=Standard
-URIDate 2020-01-01

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Balance Type:	debit
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- Definition

The amount of revenue that was included in the contract liability balance at the beginning of the period. [Refer: Contract liabilities; Revenue from contracts with customers]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 15
-IssueDate 2020-01-01
-Paragraph 116
-Subparagraph b
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=15&code=ifrs-tx-2020-en-r&anchor=para_116_b&doctype=Standard
-URIDate 2020-01-01

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- Definition

The amount of the transaction price allocated to the performance obligations that are unsatisfied (or partially unsatisfied) as of the end of the reporting period. The transaction price is the amount of consideration to which an entity expects to be entitled in exchange for transferring promised goods or services to a customer, excluding amounts collected on behalf of third parties (for example, some sales taxes). [Refer: Performance obligations [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 15
-IssueDate 2020-01-01
-Paragraph 120
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=15&code=ifrs-tx-2020-en-r&anchor=para_120_a&doctype=Standard
-URIDate 2020-01-01

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- Definition

Disclosure of additional information about revenue.

+ References

No definition available.

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