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Financial Instruments - Foreign Currency Risk Sensitivity Analysis (Detail) - TWD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Profit and loss [Member] | Financial instruments [Member] | USD [Member]
Disclosure of detailed information about financial instruments [Line Items]
Sensitivity analysis due to a 5% increase or decrease in foreign currency exchange	$ 56	$ 97	$ 83
Profit and loss [Member] | Financial instruments [Member] | EUR [Member]
Disclosure of detailed information about financial instruments [Line Items]
Sensitivity analysis due to a 5% increase or decrease in foreign currency exchange	(41)	(47)	(10)
Profit and loss [Member] | Financial instruments [Member] | SGD [Member]
Disclosure of detailed information about financial instruments [Line Items]
Sensitivity analysis due to a 5% increase or decrease in foreign currency exchange	(85)	(44)	(52)
Profit and loss [Member] | Financial instruments [Member] | JPY [Member]
Disclosure of detailed information about financial instruments [Line Items]
Sensitivity analysis due to a 5% increase or decrease in foreign currency exchange	1	1	0
Profit and loss [Member] | Financial instruments [Member] | RMB [Member]
Disclosure of detailed information about financial instruments [Line Items]
Sensitivity analysis due to a 5% increase or decrease in foreign currency exchange	3	1	0
Profit and loss [Member] | Financial instruments [Member] | HKD [Member]
Disclosure of detailed information about financial instruments [Line Items]
Sensitivity analysis due to a 5% increase or decrease in foreign currency exchange	3	3	(1)
Profit and loss [Member] | Derivatives [Member] | USD [Member]
Disclosure of detailed information about financial instruments [Line Items]
Sensitivity analysis due to a 5% increase or decrease in foreign currency exchange	0	(19)	1
Profit and loss [Member] | Derivatives [Member] | EUR [Member]
Disclosure of detailed information about financial instruments [Line Items]
Sensitivity analysis due to a 5% increase or decrease in foreign currency exchange	13	3	3
Equity [member] | Derivatives [Member] | EUR [Member]
Disclosure of detailed information about financial instruments [Line Items]
Sensitivity analysis due to a 5% increase or decrease in foreign currency exchange	$ 11	$ 10	$ 4

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