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Subsidiaries - Detailed Information of Equity Transactions (Detail) - TWD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
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 |  | $ 83
The proportionate share of the carrying amount of the net assets of the subsidiary transferred (to) from noncontrolling interests | (330) |  | (25)
Differences arising from equity transactions | 712 |  | 58
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 |  | 58
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 | 1,175
The proportionate share of the carrying amount of the net assets of the subsidiary transferred (to) from noncontrolling interests |  | (1,750) | (786)
Differences arising from equity transactions |  | 802 | 389
Additional paid-in capital - arising from changes in equities of subsidiaries |  | 802 | $ 389
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 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 | 35 |  |
The proportionate share of the carrying amount of the net assets of the subsidiary transferred (to) from noncontrolling interests | (24) |  |
Differences arising from equity transactions | 11 |  |
Additional paid-in capital - arising from changes in equities of subsidiaries | $ 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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