Investments Accounted for Using Equity Method - Market Prices of Investments Accounted for Using Equity Method in Publicly Traded Stocks Calculated by Closing Price at End of Reporting Period (Detail) - Level 1 [member] - TWD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Vanguard International Semiconductor Corporation [member]
Disclosure of associates [line items]
Closing Price in Active Markets	$ 54,778.4	$ 53,849.9
Global Unichip Corporation [member]
Disclosure of associates [line items]
Closing Price in Active Markets	19,282.1	15,827.2
Xintec Inc. [member]
Disclosure of associates [line items]
Closing Price in Active Markets	$ 18,806.6	$ 20,420.2

Investments Accounted for Using Equity Method - Market Prices of Investments Accounted for Using Equity Method in Publicly Traded Stocks Calculated by Closing Price at End of Reporting Period (Detail) - Level 1 [member] - TWD ($)
$ in Millions

Jun. 30, 2021

Dec. 31, 2020

Vanguard International Semiconductor Corporation [member]

Disclosure of associates [line items]

Closing Price in Active Markets

$ 54,778.4

$ 53,849.9

Global Unichip Corporation [member]

Disclosure of associates [line items]

Closing Price in Active Markets

19,282.1

15,827.2

Xintec Inc. [member]

Disclosure of associates [line items]

Closing Price in Active Markets

$ 18,806.6

$ 20,420.2