Revenue - Summary of Incremental Costs of Obtaining Contracts (Detail) $ in Millions, $ in Millions	Dec. 31, 2020 TWD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 TWD ($)
Revenue [Abstract]
Incremental costs of obtaining a contract	$ 1,000	$ 36	$ 943

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

Name:	ifrs-full_AssetsRecognisedFromCostsToObtainOrFulfilContractsWithCustomers
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant