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Subsidiaries - Detailed Information of Equity Transactions (Detail) - TWD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Chunghwa Investment Co Ltd Did Not Participate In The Capital Increase Of Chunghwa Precision Test Tech Co Ltd [Member] |  |  |
Disclosure Of Classes Of Share Capital [Line Items] |  |  |
Cash consideration received from (paid to)Noncontrolling interests |  |  | $ 2,552
The proportionate share of the carrying amount of the net assets of the subsidiary transferred (to) from noncontrolling interests |  |  | (1,750)
Differences arising from equity transactions |  |  | 802
Additional paid-in capital - arising from changes in equities of subsidiaries |  |  | 802
Senao International Co Ltd Transferred Its Treasury Stock [Member] |  |  |
Disclosure Of Classes Of Share Capital [Line Items] |  |  |
Cash consideration received from (paid to)Noncontrolling interests |  | $ 327 | 164
The proportionate share of the carrying amount of the net assets of the subsidiary transferred (to) from noncontrolling interests |  | (272) | (137)
Differences arising from equity transactions |  | 55 | 27
Additional paid-in capital - arising from changes in equities of subsidiaries |  | 55 | 27
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 (paid to)Noncontrolling interests |  | 133 | 106
The proportionate share of the carrying amount of the net assets of the subsidiary transferred (to) from noncontrolling interests |  | (19) | (29)
Differences arising from equity transactions |  | 114 | 77
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 | $ 77
SENAO not Proportionately participating in the Capital Increase of Youth [Member] |  |  |
Disclosure Of Classes Of Share Capital [Line Items] |  |  |
Cash consideration received from (paid to)Noncontrolling interests |  | 0 |
The proportionate share of the carrying amount of the net assets of the subsidiary transferred (to) from noncontrolling interests |  | 0 |
Differences arising from equity transactions |  | 0 |
Additional paid-in capital - difference between consideration received or paid and the carrying amount of the subsidiaries net assets upon actual disposal or acquisition |  | 0 |
Additional paid-in capital - arising from changes in equities of subsidiaries |  | 0 |
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 (paid to)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 (paid to)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 (paid to)Noncontrolling interests | $ 19 | 35 |
The proportionate share of the carrying amount of the net assets of the subsidiary transferred (to) from noncontrolling interests | (20) | (24) |
Differences arising from equity transactions | (1) | 11 |
Additional paid-in capital - arising from changes in equities of subsidiaries | $ (1) | $ 11 |

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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 2019-01-01 -Paragraph 106 -Subparagraph d -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_106_d&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The amount of consideration paid or received in respect of both obtaining and losing control of subsidiaries or other businesses. [Refer: Subsidiaries [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 7 -IssueDate 2019-01-01 -Paragraph 40 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=7&code=ifrs-tx-2019-en-r&anchor=para_40_a&doctype=Standard -URIDate 2019-03-27 + Details
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