Contents of Significant Accounts - Business Combinations - Additional Information (Detail) - 12 months ended Dec. 31, 2019 $ in Millions, ¥ in Billions	TWD ($)	JPY (¥)
MIE FUJITSU SEMICONDUCTOR LIMITED (MIFS) [member]
Disclosure of detailed information about business combination [line items]
Percentage of equity interest acquired		84.10%
Percentage of equity interest previously held		15.90%
Cash Consideration of Business Combination \| ¥		¥ 54.4
UNITED SEMICONDUCTOR JAPAN CO LTD (USJC) [member]
Disclosure of detailed information about business combination [line items]
Operating Revenue of Business acquisition	$ 4,277
Profit before tax From operations	305
Gain (loss) on disposal of equity method	375
Operating Revenue of Business acquisition	160,767
Profit before tax From operations	$ 5,606

The fair value, at acquisition date, of cash transferred as consideration in a business combination. [Refer: Business combinations [member]]

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The cumulative gain (loss) on disposal of investments in equity instruments that the entity has designated at fair value through other comprehensive income. [Refer: At fair value [member]; Other comprehensive income]

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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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The percentage of voting equity interests acquired in a business combination. [Refer: Business combinations [member]]

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The profit (loss) of the acquiree, since the acquisition date, included in the consolidated statement of comprehensive income. [Refer: Profit (loss)]

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The profit (loss) of the combined entity as though the acquisition date for all business combinations that occurred during the year had been as of the beginning of the annual reporting period. [Refer: Business combinations [member]; Profit (loss)]

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The amount of revenue of the acquiree since the acquisition date included in the consolidated statement of comprehensive income. [Refer: Revenue]

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The revenue of the combined entity as though the acquisition date for all business combinations that occurred during the year had been as of the beginning of the annual reporting period. [Refer: Business combinations [member]; Revenue]

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The percentage of acquirer's previously held voting equity interests in the acquiree.

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