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Net Income and Other Comprehensive Income (Loss) - Reclassification Adjustments of Other Comprehensive Income (Loss) (Detail) $ in Millions, $ in Millions | 12 Months Ended
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Dec. 31, 2017 TWD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 TWD ($) | Dec. 31, 2015 TWD ($)
Unrealized gain (loss) on available-for-sale financial assets |  |  |  |
Arising during the year | $ 605 |  | $ (721) | $ (671)
Reclassification adjustments |  |  |  |
Upon disposal | 0 |  | 0 | 0
Upon impairment | 0 |  | 577 | 26
Unrealized gain (loss) on available-for- sale financial assets | 605 | $ 21 | (144) | (645)
Cash flow hedges |  |  |  |
Gain arising during the year | 3 |  | 15 | 18
Reclassification adjustments included in profit or loss | (2) |  | (1) | 1
Adjusted against the carrying amount of hedged items | (2) |  | (15) | (18)
Cash flow hedges | $ (1) | $ 0 | $ (1) | $ 1

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- Definition Reclassification to profit of loss upon disposal. + References No definition available. + Details
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- Definition The amounts removed from equity and included in the initial cost or other carrying amount of a non-financial asset (liability) whose acquisition or incurrence was a hedged, highly probable forecast transaction, before tax. [Refer: Carrying amount [member]] + 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 23 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2016-03-30&anchor=para_23_e&doctype=Standard -URIDate 2016-03-31 + Details
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- Definition The gains (losses) recognised in other comprehensive income on cash flow hedges, before tax. [Refer: Cash flow hedges [member]] + 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 23 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2016-03-30&anchor=para_23_c&doctype=Standard -URIDate 2016-03-31 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2016-01-13 -Paragraph 91 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2016-03-30&anchor=para_91_b&doctype=Standard -URIDate 2016-03-31 + Details
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- Definition The gains (losses) recognised in other comprehensive income on remeasuring available-for-sale financial assets, before tax. [Refer: Financial assets available-for-sale] + 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 20 -Subparagraph a -Clause ii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2016-03-30&anchor=para_20_a_ii&doctype=Standard -URIDate 2016-03-31 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Note Expiry date 2018-01-01 -Name IAS -Number 1 -IssueDate 2016-01-13 -Paragraph 91 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2016-03-30&anchor=para_91_b&doctype=Standard -URIDate 2016-03-31 + Details
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- Definition The amount of impairment loss recognised in other comprehensive income. Impairment loss on a revalued asset is recognised in other comprehensive income to the extent that the impairment loss does not exceed the amount in the revaluation surplus for that same asset. [Refer: Impairment loss; Revaluation surplus; Other comprehensive income] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 36 -IssueDate 2016-01-13 -Paragraph 126 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=36&date=2016-03-30&anchor=para_126_c&doctype=Standard -URIDate 2016-03-31 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 36 -IssueDate 2016-01-13 -Paragraph 129 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=36&date=2016-03-30&anchor=para_129_a&doctype=Standard -URIDate 2016-03-31 + Details
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- Definition The amount of other comprehensive income, before tax, related to available-for-sale financial assets. [Refer: Financial assets available-for-sale; Other comprehensive income, before tax] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Note Expiry date 2018-01-01 -Name IAS -Number 1 -IssueDate 2016-01-13 -Paragraph 91 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2016-03-30&anchor=para_91_b&doctype=Standard -URIDate 2016-03-31 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Note Expiry date 2018-01-01 -Name IAS -Number 1 -IssueDate 2016-01-13 -Paragraph 7 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2016-03-30&anchor=para_7&doctype=Standard -URIDate 2016-03-31 + Details
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- Definition The amount of other comprehensive income, before tax, related to cash flow hedges. [Refer: Cash flow hedges [member]; Other comprehensive income, before tax] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2016-01-13 -Paragraph 91 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2016-03-30&anchor=para_91_b&doctype=Standard -URIDate 2016-03-31 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2016-01-13 -Paragraph 7 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2016-03-30&anchor=para_7&doctype=Standard -URIDate 2016-03-31 + Details
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- Definition The amount of reclassification adjustments related to cash flow hedges, before tax. Reclassification adjustments are amounts reclassified to profit (loss) in the current period that were recognised in other comprehensive income in the current or previous periods. [Refer: Cash flow hedges [member]; Other comprehensive income] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2016-01-13 -Paragraph 92 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2016-03-30&anchor=para_92&doctype=Standard -URIDate 2016-03-31 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Note Expiry date 2018-01-01 -Name IFRS -Number 7 -IssueDate 2016-01-13 -Paragraph 23 -Subparagraph d -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2016-03-30&anchor=para_23_d&doctype=Standard -URIDate 2016-03-31 + Details
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