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Subsidiaries - Detailed Information of Equity Transactions (Detail) - TWD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Senao International Co Ltd Transferred Its Treasury Stock [Member] |  |  |
Disclosure Of Classes Of Share Capital [Line Items] |  |  |
Cash consideration received from noncontrolling interests |  |  | $ 327
The proportionate share of the carrying amount of the net assets of the subsidiary transferred (to) from noncontrolling interests |  |  | (272)
Differences arising from equity transactions |  |  | 55
Additional paid-in capital - arising from changes in equities of subsidiaries |  |  | 55
Chunghwa Telecom Co Ltd and Chunghwa Investment Co Ltd Disposed Some Shares of CHIEF Telecom Inc [Member] |  |  |
Disclosure Of Classes Of Share Capital [Line Items] |  |  |
Cash consideration received from noncontrolling interests |  |  | 133
The proportionate share of the carrying amount of the net assets of the subsidiary transferred (to) from noncontrolling interests |  |  | (19)
Differences arising from equity transactions |  |  | 114
Additional paid-in capital - difference between consideration received or paid and the carrying amount of the subsidiaries net assets upon actual disposal or acquisition |  |  | 114
Chunghwa Investment Co Ltd Disposed Some Shares Of Chunghwa Precision Test Tech Co Ltd |  |  |
Disclosure Of Classes Of Share Capital [Line Items] |  |  |
Cash consideration received from noncontrolling interests |  |  | 1,042
The proportionate share of the carrying amount of the net assets of the subsidiary transferred (to) from noncontrolling interests |  |  | (330)
Differences arising from equity transactions |  |  | 712
Additional paid-in capital - difference between consideration received or paid and the carrying amount of the subsidiaries net assets upon actual disposal or acquisition |  |  | 712
Chunghwa Telecom Co Ltd and Chunghwa Investment Co Ltd Did Not Participate in the Capital Increase of CHIEF Telecom Inc [Member] |  |  |
Disclosure Of Classes Of Share Capital [Line Items] |  |  |
Cash consideration received from noncontrolling interests |  |  | 1,477
The proportionate share of the carrying amount of the net assets of the subsidiary transferred (to) from noncontrolling interests |  |  | (700)
Differences arising from equity transactions |  |  | 777
Additional paid-in capital - arising from changes in equities of subsidiaries |  |  | 777
Share-Based Payment of CHIEF Telecom Inc [Member] |  |  |
Disclosure Of Classes Of Share Capital [Line Items] |  |  |
Cash consideration received from noncontrolling interests | $ 75 | $ 19 | 35
The proportionate share of the carrying amount of the net assets of the subsidiary transferred (to) from noncontrolling interests | (49) | (20) | (24)
Differences arising from equity transactions | 26 | (1) | 11
Additional paid-in capital - arising from changes in equities of subsidiaries | 26 | $ (1) | 11
SENAO not Proportionately participating in the Capital Increase of Youth [Member] |  |  |
Disclosure Of Classes Of Share Capital [Line Items] |  |  |
Cash consideration received from noncontrolling interests | 0 |  | 0
The proportionate share of the carrying amount of the net assets of the subsidiary transferred (to) from noncontrolling interests | 0 |  | 0
Differences arising from equity transactions | 0 |  | 0
Additional paid-in capital - arising from changes in equities of subsidiaries | 0 |  | $ 0
IISI Share-Based Payment [Member] |  |  |
Disclosure Of Classes Of Share Capital [Line Items] |  |  |
Cash consideration received from noncontrolling interests | 7 |  |
The proportionate share of the carrying amount of the net assets of the subsidiary transferred (to) from noncontrolling interests | (7) |  |
Differences arising from equity transactions | 0 |  |
Additional paid-in capital - arising from changes in equities of subsidiaries | $ 0 |  |

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- Definition Difference between consideration received or paid and carrying amount of subsidiaries' net assets upon actual disposal or acquisition effect on additional paid-in capital. + References No definition available. + Details
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- Definition The increase (decrease) in equity. [Refer: Equity] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2020-01-01 -Paragraph 106 -Subparagraph d -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_106_d&doctype=Standard -URIDate 2020-01-01 + Details
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