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Property, Plant and Equipment - Additional Information (Detail) $ in Millions | 12 Months Ended
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Dec. 31, 2019 TWD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 TWD ($) | Dec. 31, 2017 TWD ($)
Disclosure Of Property Plant And Equipment [Line Items] |  |  |  |
Impairment loss on property, plant and equipment | $ 93,000,000 | $ 4 | $ 0 | $ 0
Assets Subject to Operating Leases [Member] | Land [Member] | Bottom of Range [Member] |  |  |  |
Disclosure Of Property Plant And Equipment [Line Items] |  |  |  |
Lease period | 1 year | 1 year |  |
Assets Subject to Operating Leases [Member] | Land [Member] | Top of Range [Member] |  |  |  |
Disclosure Of Property Plant And Equipment [Line Items] |  |  |  |
Lease period | 20 years | 20 years |  |
Assets Subject to Operating Leases [Member] | Buildings [Member] | Bottom of Range [Member] |  |  |  |
Disclosure Of Property Plant And Equipment [Line Items] |  |  |  |
Lease period | 1 year | 1 year |  |
Assets Subject to Operating Leases [Member] | Buildings [Member] | Top of Range [Member] |  |  |  |
Disclosure Of Property Plant And Equipment [Line Items] |  |  |  |
Lease period | 20 years | 20 years |  |
Chunghwa Precision Test Tech. Co., Ltd. (CHPT) [Member] | Assets Used by the Company [Member] |  |  |  |
Disclosure Of Property Plant And Equipment [Line Items] |  |  |  |
Recoverable amount of asset | $ 0 |  |  |
Impairment loss on property, plant and equipment | 89,000,000 |  |  |
Chunghwa System Integration Co., Ltd. (CHSI) [Member] | Assets Used by the Company [Member] |  |  |  |
Disclosure Of Property Plant And Equipment [Line Items] |  |  |  |
Recoverable amount of asset | 0 |  |  |
Impairment loss on property, plant and equipment | $ 4,000,000 |  |  |

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- Definition The amount of impairment loss recognised in profit or loss for property, plant and equipment. [Refer: Impairment loss recognised in profit or loss; Property, plant and equipment] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 16 -IssueDate 2019-01-01 -Paragraph 73 -Subparagraph e -Clause v -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=16&code=ifrs-tx-2019-en-r&anchor=para_73_e_v&doctype=Standard -URIDate 2019-03-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2019-01-01 -Paragraph 98 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_98_a&doctype=Standard -URIDate 2019-03-27 + Details
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