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Revenue - Summary of Revenue (Detail) $ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020 TWD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 TWD ($)	Dec. 31, 2018 TWD ($)
Revenue [Abstract]
Revenue from contracts with customers	$ 206,396		$ 206,360	$ 214,461
Other revenues
Rental income	843		818	640
Others	370		342	382
Revenue other than from contracts with customers	1,213		1,160	1,022
Total	$ 207,609	$ 7,393	$ 207,520	$ 215,483

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Other revenues.

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Rental Income from operating activities.

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Revenue other than from contracts with customers.

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The amount of operating income that the entity does not separately disclose in the same statement or note.

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The income arising in the course of an entity's ordinary activities. Income is increases in assets, or decreases in liabilities, that result in increases in equity, other than those relating to contributions from holders of equity claims.

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The amount of revenue from contracts with customers. A customer is a party that has contracted with an entity to obtain goods or services that are an output of the entity’s ordinary activities in exchange for consideration.

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