Operating Segments Information - Major Customers Representing at Least 10 Percent of Net Revenue (Detail) $ in Millions, $ in Millions	12 Months Ended
Dec. 31, 2020 TWD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 TWD ($)	Dec. 31, 2018 TWD ($)
Disclosure of major customers [line items]
NET REVENUE	$ 1,339,254.8	$ 47,694.3	$ 1,069,985.4	$ 1,031,473.6
Customer A [member]
Disclosure of major customers [line items]
NET REVENUE	$ 336,775.5		$ 247,213.3	$ 224,690.7
Percentage of entity's revenue	25.00%	25.00%	23.00%	22.00%
Customer B [member]
Disclosure of major customers [line items]
NET REVENUE	$ 167,390.8		$ 152,876.9	$ 83,885.6
Percentage of entity's revenue	12.00%	12.00%	14.00%	8.00%

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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+ Details