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Retirement Benefit Plans - Pension Costs Recognized in Profit and Loss for Defined Benefit Plans (Detail) - TWD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Disclosure Of Defined Plan [line items] |  |  |
Defined benefit plans pension costs recognized in profit and loss | $ 2,859 | $ 2,953 | $ 2,834
Operating costs [Member] |  |  |
Disclosure Of Defined Plan [line items] |  |  |
Defined benefit plans pension costs recognized in profit and loss | 1,726 | 1,796 | 1,734
Marketing expenses [Member] |  |  |
Disclosure Of Defined Plan [line items] |  |  |
Defined benefit plans pension costs recognized in profit and loss | 866 | 886 | 847
General and administrative expenses [Member] |  |  |
Disclosure Of Defined Plan [line items] |  |  |
Defined benefit plans pension costs recognized in profit and loss | 164 | 164 | 156
Research and development expenses [Member] |  |  |
Disclosure Of Defined Plan [line items] |  |  |
Defined benefit plans pension costs recognized in profit and loss | $ 103 | $ 107 | $ 97

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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 post-employment benefit expense relating to defined benefit plans. [Refer: Defined benefit plans [member]] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 19 -IssueDate 2019-01-01 -Paragraph 5 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2019-en-r&anchor=para_5&doctype=Standard -URIDate 2019-03-27 + Details
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