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Segment Information - Other Segment Information (Detail) $ in Millions, $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 TWD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 TWD ($) | Dec. 31, 2016 TWD ($)
Disclosure of operating segments [Line Items] |  |  |  |
Share of the profits of associates and joint ventures accounted for using equity method | $ 509 | $ 17 | $ 419 | $ 515
Interest income | 197 | 7 | 205 | 189
Interest expenses | 18 | 1 | 22 | 20
Operating costs and expenses | 171,949 |  | 180,706 | 181,390
Depreciation and amortization | 33,809 |  | 31,930 | 32,485
Capital expenditure | 28,550 | 933 | 26,875 | 23,517
Impairment loss on property, plant and equipment | 0 | 0 | 0 | 596
Reversal of impairment loss | 19 | $ 1 | 11 | 148
Domestic Fixed Communications Business [Member] |  |  |  |
Disclosure of operating segments [Line Items] |  |  |  |
Interest income | 18 |  | 21 | 15
Operating costs and expenses | 59,430 |  | 62,795 | 64,230
Depreciation and amortization | 15,027 |  | 15,614 | 16,414
Capital expenditure | 12,693 |  | 11,647 | 9,846
Reversal of impairment loss | 19 |  | 11 | 148
Mobile Communications Business [Member] |  |  |  |
Disclosure of operating segments [Line Items] |  |  |  |
Interest income | 12 |  | 15 | 11
Interest expenses | 0 |  | 6 | 2
Operating costs and expenses | 73,901 |  | 80,275 | 79,593
Depreciation and amortization | 13,788 |  | 11,001 | 10,620
Capital expenditure | 10,664 |  | 9,742 | 8,981
Impairment loss on property, plant and equipment |  |  |  | 596
Internet Business [Member] |  |  |  |
Disclosure of operating segments [Line Items] |  |  |  |
Interest income | 19 |  | 9 | 7
Operating costs and expenses | 13,766 |  | 13,288 | 13,160
Depreciation and amortization | 3,121 |  | 3,385 | 3,626
Capital expenditure | 2,729 |  | 2,779 | 2,718
International Fixed Communications Business [Member] |  |  |  |
Disclosure of operating segments [Line Items] |  |  |  |
Interest income | 28 |  | 15 | 6
Operating costs and expenses | 13,279 |  | 13,385 | 14,313
Depreciation and amortization | 1,425 |  | 1,477 | 1,451
Capital expenditure | 1,348 |  | 1,580 | 1,136
Other [Member] |  |  |  |
Disclosure of operating segments [Line Items] |  |  |  |
Share of the profits of associates and joint ventures accounted for using equity method | 509 |  | 419 | 515
Interest income | 120 |  | 145 | 150
Interest expenses | 18 |  | 16 | 18
Operating costs and expenses | 11,573 |  | 10,963 | 10,094
Depreciation and amortization | 448 |  | 453 | 374
Capital expenditure | $ 1,116 |  | $ 1,127 | $ 836

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