Financial Instruments - Assets and Liabilities related to Foreign Currency Risk (Detail) - Foreign currency risk [Member] - TWD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
USD [Member]
Disclosure of detailed information about financial instruments [Line Items]
Foreign currency denominated monetary assets	$ 2,711	$ 5,782
Foreign currency denominated monetary liabilities	768	4,121
Derivatives assets	0	0
Derivatives liabilities	0	0
EUR [Member]
Disclosure of detailed information about financial instruments [Line Items]
Foreign currency denominated monetary assets	15	12
Foreign currency denominated monetary liabilities	957	206
Derivatives assets	4	0
Derivatives liabilities	0	0
SGD [Member]
Disclosure of detailed information about financial instruments [Line Items]
Foreign currency denominated monetary assets	170	225
Foreign currency denominated monetary liabilities	1,049	1,263
RMB [Member]
Disclosure of detailed information about financial instruments [Line Items]
Foreign currency denominated monetary assets	30	9
Foreign currency denominated monetary liabilities	0	0
JPY [Member]
Disclosure of detailed information about financial instruments [Line Items]
Foreign currency denominated monetary assets	22	17
Foreign currency denominated monetary liabilities	10	14
HKD [Member]
Disclosure of detailed information about financial instruments [Line Items]
Foreign currency denominated monetary assets	69	0
Foreign currency denominated monetary liabilities	$ 8	$ 15

The amount of financial assets classified as derivative instruments. [Refer: Financial assets; Derivatives [member]]

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The amount of financial liabilities classified as derivative instruments. [Refer: Financial assets; Derivatives [member]]

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Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

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No definition available.

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The amount of assets that are: (a) cash; (b) an equity instrument of another entity; (c) a contractual right: (i) to receive cash or another financial asset from another entity; or (ii) to exchange financial assets or financial liabilities with another entity under conditions that are potentially favourable to the entity; or (d) a contract that will, or may be, settled in the entity’s own equity instruments and is: (i) a non-derivative for which the entity is, or may be, obliged to receive a variable number of the entity’s own equity instruments; or (ii) a derivative that will, or may be, settled other than by the exchange of a fixed amount of cash or another financial asset for a fixed number of the entity’s own equity instruments. For this purpose the entity’s own equity instruments do not include puttable financial instruments classified as equity instruments in accordance with paragraphs 16A-16B of IAS 32, instruments that impose on the entity an obligation to deliver to another party a pro rata share of the net assets of the entity only on liquidation and are classified as equity instruments in accordance with paragraphs 16C-16D of IAS 32, or instruments that are contracts for the future receipt or delivery of the entity’s own equity instruments. [Refer: Financial instruments, class [member]; Financial liabilities]

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- Definition

The amount of liabilities that are: (a) a contractual obligation: (i) to deliver cash or another financial asset to another entity; or (ii) to exchange financial assets or financial liabilities with another entity under conditions that are potentially unfavourable to the entity; or (b) a contract that will, or may be, settled in the entity’s own equity instruments and is: (i) a non-derivative for which the entity is, or may be, obliged to deliver a variable number of the entity’s own equity instruments; or (ii) a derivative that will, or may be, settled other than by the exchange of a fixed amount of cash or another financial asset for a fixed number of the entity’s own equity instruments. For this purpose, rights, options or warrants to acquire a fixed number of the entity’s own equity instruments for a fixed amount of any currency are equity instruments if the entity offers the rights, options or warrants pro rata to all of its existing owners of the same class of its own non-derivative equity instruments. Also, for those purposes the entity’s own equity instruments do not include puttable financial instruments that are classified as equity instruments in accordance with paragraphs 16A-16B of IAS 32, instruments that impose on the entity an obligation to deliver to another party a pro rata share of the net assets of the entity only on liquidation and are classified as equity instruments in accordance with paragraphs 16C-16D of IAS 32, or instruments that are contracts for the future receipt or delivery of the entity’s own equity instruments. As an exception, an instrument that meets the definition of a financial liability is classified as an equity instrument if it has all the features and meets the conditions in paragraphs 16A-16B or paragraphs 16C-16D of IAS 32. [Refer: Financial instruments, class [member]; Financial assets; Derivatives [member]]

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