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Fair Value Information - Carrying Amounts of Financial Assets and Liabilities Not Measured at Fair Value (Detail) - TWD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016
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Disclosure of fair value measurement of assets [Line Items] |  |
Held-to-maturity financial assets | $ 0 | $ 2,140
Corporate bonds [Member] |  |
Disclosure of fair value measurement of assets [Line Items] |  |
Held-to-maturity financial assets |  | 1,990
Bank debentures [Member] |  |
Disclosure of fair value measurement of assets [Line Items] |  |
Held-to-maturity financial assets |  | 150
Not measured at fair value [Member] |  |
Disclosure of fair value measurement of assets [Line Items] |  |
Held-to-maturity financial assets |  | 2,140
Not measured at fair value [Member] | Corporate bonds [Member] |  |
Disclosure of fair value measurement of assets [Line Items] |  |
Held-to-maturity financial assets |  | 1,990
Not measured at fair value [Member] | Bank debentures [Member] |  |
Disclosure of fair value measurement of assets [Line Items] |  |
Held-to-maturity financial assets |  | 150
Not measured at fair value [Member] | Level 2 [Member] |  |
Disclosure of fair value measurement of assets [Line Items] |  |
Held-to-maturity financial assets |  | 2,146
Not measured at fair value [Member] | Level 2 [Member] | Corporate bonds [Member] |  |
Disclosure of fair value measurement of assets [Line Items] |  |
Held-to-maturity financial assets |  | 1,996
Not measured at fair value [Member] | Level 2 [Member] | Bank debentures [Member] |  |
Disclosure of fair value measurement of assets [Line Items] |  |
Held-to-maturity financial assets |  | $ 150

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- Definition 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. + References No definition available. + Details
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- Definition The amount of non-derivative financial assets with fixed or determinable payments and fixed maturity that an entity has the positive intention and ability to hold to maturity other than: (a) those that the entity upon initial recognition designates as at fair value through profit or loss; (b) those that the entity designates as available for sale; and (c) those that meet the definition of loans and receivables. An entity shall not classify any financial assets as held to maturity if the entity has, during the current financial year or during the two preceding financial years, sold or reclassified more than an insignificant amount of held-to-maturity investments before maturity (more than insignificant in relation to the total amount of held-to-maturity investments) other than sales or reclassifications that: (i) are so close to maturity or the financial asset’s call date (for example, less than three months before maturity) that changes in the market rate of interest would not have a significant effect on the financial asset’s fair value; (ii) occur after the entity has collected substantially all of the financial asset’s original principal through scheduled payments or prepayments; or (iii) are attributable to an isolated event that is beyond the entity’s control, is non-recurring and could not have been reasonably anticipated by the entity. [Refer: Derivative financial assets; Held-to-maturity investments; Prepayments] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Note Expiry date 2018-01-01 -Name IFRS -Number 7 -IssueDate 2016-01-13 -Paragraph 8 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2016-03-30&anchor=para_8_b&doctype=Standard -URIDate 2016-03-31 + Details
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