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Income Tax - Movements of Deferred Income Tax Assets and Liabilities (Detail) - TWD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Income tax [Line Items] |  |  |
Recognized in Profit or Loss | $ 81 | $ 63 | $ (208)
Recognized in Other Comprehensive Income | (239) | (305) | 450
Deferred tax asset [Member] |  |  |
Income tax [Line Items] |  |  |
Beginning balance | 3,259 | 3,554 | 2,730
Effect of Retrospective Application of IFRS 16 |  | 26 |
Acquired by business combinations (Note 14) | 6 |  |
Recognized in Profit or Loss | 107 | (16) | 374
Recognized in Other Comprehensive Income | (239) | (305) | 450
Ending balance | 3,133 | 3,259 | 3,554
Deferred tax asset [Member] | Allowance for doubtful receivables over quota [Member] |  |  |
Income tax [Line Items] |  |  |
Beginning balance | 404 | 435 | 289
Recognized in Profit or Loss | (39) | (31) | 146
Ending balance | 365 | 404 | 435
Deferred tax asset [Member] | Share of profits of associates and joint ventures accounted for using equity method [Member] |  |  |
Income tax [Line Items] |  |  |
Beginning balance | 402 | 389 | 331
Recognized in Profit or Loss | (1) | 13 | 58
Ending balance | 401 | 402 | 389
Deferred tax asset [Member] | Defined benefit pension plans [Member] |  |  |
Income tax [Line Items] |  |  |
Beginning balance | 2,034 | 2,307 | 1,723
Acquired by business combinations (Note 14) | 1 |  |
Recognized in Profit or Loss | 20 | 32 | 134
Recognized in Other Comprehensive Income | (239) | (305) | 450
Ending balance | 1,816 | 2,034 | 2,307
Deferred tax asset [Member] | Valuation loss on inventory [Member] |  |  |
Income tax [Line Items] |  |  |
Beginning balance | 141 | 88 | 23
Acquired by business combinations (Note 14) | 3 |  |
Recognized in Profit or Loss | 155 | 53 | 65
Ending balance | 299 | 141 | 88
Deferred tax asset [Member] | Deferred revenue [Member] |  |  |
Income tax [Line Items] |  |  |
Beginning balance | 98 | 111 | 106
Recognized in Profit or Loss | (25) | (13) | 5
Ending balance | 73 | 98 | 111
Deferred tax asset [Member] | Estimated warranty liabilities [Member] |  |  |
Income tax [Line Items] |  |  |
Beginning balance | 34 | 26 | 22
Recognized in Profit or Loss | 2 | 8 | 4
Ending balance | 36 | 34 | 26
Deferred tax asset [Member] | Accrued award credits liabilities [Member] |  |  |
Income tax [Line Items] |  |  |
Beginning balance | 17 | 14 | 15
Recognized in Profit or Loss | 1 | 3 | (1)
Ending balance | 18 | 17 | 14
Deferred tax asset [Member] | Others [Member] |  |  |
Income tax [Line Items] |  |  |
Beginning balance | 101 | 143 | 175
Effect of Retrospective Application of IFRS 16 |  | 26 |
Acquired by business combinations (Note 14) | 2 |  |
Recognized in Profit or Loss | 2 | (68) | (32)
Ending balance | 105 | 101 | 143
Deferred tax asset [Member] | Temporary differences [Member] |  |  |
Income tax [Line Items] |  |  |
Beginning balance | 3,231 | 3,513 | 2,684
Effect of Retrospective Application of IFRS 16 |  | 26 |
Acquired by business combinations (Note 14) | 6 |  |
Recognized in Profit or Loss | 115 | (3) | 379
Recognized in Other Comprehensive Income | (239) | (305) | 450
Ending balance | 3,113 | 3,231 | 3,513
Deferred tax asset [Member] | Unused tax losses [Member] |  |  |
Income tax [Line Items] |  |  |
Beginning balance | 28 | 41 | 46
Recognized in Profit or Loss | (8) | (13) | (5)
Ending balance | 20 | 28 | 41
Deferred tax liability [Member] |  |  |
Income tax [Line Items] |  |  |
Beginning balance | (1,912) | (1,992) | (1,430)
Effect of Retrospective Application of IFRS 9 |  |  | 1
Acquired by business combinations (Note 14) | (3) |  |
Recognized in Profit or Loss | (52) | 80 | (563)
Ending balance | (1,967) | (1,912) | (1,992)
Deferred tax liability [Member] | Defined benefit pension plans [Member] |  |  |
Income tax [Line Items] |  |  |
Beginning balance | (1,758) | (1,832) | (1,265)
Recognized in Profit or Loss | (54) | 74 | (567)
Ending balance | (1,812) | (1,758) | (1,832)
Deferred tax liability [Member] | Others [Member] |  |  |
Income tax [Line Items] |  |  |
Beginning balance | (1) | (2) | (2)
Effect of Retrospective Application of IFRS 9 |  |  | 1
Acquired by business combinations (Note 14) | (3) |  |
Recognized in Profit or Loss | 1 | 1 | (1)
Ending balance | (3) | (1) | (2)
Deferred tax liability [Member] | Land value incremental tax [Member] |  |  |
Income tax [Line Items] |  |  |
Beginning balance | (95) | (95) | (95)
Ending balance | (95) | (95) | (95)
Deferred tax liability [Member] | Deferred revenue for award credits [Member] |  |  |
Income tax [Line Items] |  |  |
Beginning balance | (29) | (31) | (29)
Recognized in Profit or Loss | (1) | 2 | (2)
Ending balance | (30) | (29) | (31)
Deferred tax liability [Member] | Intangible assets and goodwill [member] |  |  |
Income tax [Line Items] |  |  |
Beginning balance | (29) | (32) | (39)
Recognized in Profit or Loss | 2 | 3 | 7
Ending balance | $ (27) | $ (29) | $ (32)

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- Definition The amount of tax expense or income relating to changes in deferred tax liabilities and deferred tax assets, recognised in profit or loss. [Refer: Deferred tax assets; Deferred tax expense (income); Deferred tax liabilities] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2020-01-01 -Paragraph 81 -Subparagraph g -Clause ii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=12&code=ifrs-tx-2020-en-r&anchor=para_81_g_ii&doctype=Standard -URIDate 2020-01-01 + Details
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