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Trade Notes and Accounts Receivable, Net - Provision Matrix Arising from Telecommunications and Project Business (Detail) $ in Millions, $ in Millions | Dec. 31, 2020 TWD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 TWD ($) | Jan. 01, 2019 TWD ($)
--- | --- | --- | --- | ---
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | $ 22,622 | $ 806 | $ 26,408 | $ 30,076
Less: Loss allowance | (2,154) |  | (2,360) |
Gross carrying amount [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | 24,776 |  | 28,768 |
Telecommunications Business [Member] | Loss allowance [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Less: Loss allowance | (797) |  | (799) |
Telecommunications Business [Member] | Gross carrying amount [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | 16,806 |  | 20,080 |
Telecommunications Business [Member] | Amortized Cost [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | $ 16,009 |  | 19,281 |
Project Business [Member] | Bottom of Range [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Expected credit loss rate | 50.00% | 50.00% |  |
Project Business [Member] | Loss allowance [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Less: Loss allowance | $ (1,320) |  | (1,502) |
Project Business [Member] | Gross carrying amount [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | 4,866 |  | 5,699 |
Project Business [Member] | Amortized Cost [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | $ 3,546 |  | $ 4,197 |
Not Past Due [Member] | Telecommunications Business [Member] | Bottom of Range [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Expected credit loss rate | 0.00% | 0.00% | 0.00% |
Not Past Due [Member] | Telecommunications Business [Member] | Top of Range [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Expected credit loss rate | 2.00% | 2.00% | 2.00% |
Not Past Due [Member] | Telecommunications Business [Member] | Loss allowance [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Less: Loss allowance | $ (56) |  | $ (56) |
Not Past Due [Member] | Telecommunications Business [Member] | Gross carrying amount [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | 15,839 |  | 19,020 |
Not Past Due [Member] | Telecommunications Business [Member] | Amortized Cost [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | $ 15,783 |  | $ 18,964 |
Not Past Due [Member] | Project Business [Member] | Bottom of Range [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Expected credit loss rate | 0.00% | 0.00% | 0.00% |
Not Past Due [Member] | Project Business [Member] | Top of Range [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Expected credit loss rate | 5.00% | 5.00% | 5.00% |
Not Past Due [Member] | Project Business [Member] | Loss allowance [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Less: Loss allowance | $ (20) |  | $ (3) |
Not Past Due [Member] | Project Business [Member] | Gross carrying amount [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | 3,473 |  | 4,054 |
Not Past Due [Member] | Project Business [Member] | Amortized Cost [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | $ 3,453 |  | $ 4,051 |
Less Than 30 Days [Member] | Telecommunications Business [Member] | Bottom of Range [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Expected credit loss rate | 2.00% | 2.00% | 0.00% |
Less Than 30 Days [Member] | Telecommunications Business [Member] | Top of Range [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Expected credit loss rate | 24.00% | 24.00% | 25.00% |
Less Than 30 Days [Member] | Telecommunications Business [Member] | Loss allowance [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Less: Loss allowance | $ (21) |  | $ (26) |
Less Than 30 Days [Member] | Telecommunications Business [Member] | Gross carrying amount [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | 204 |  | 268 |
Less Than 30 Days [Member] | Telecommunications Business [Member] | Amortized Cost [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | $ 183 |  | $ 242 |
Less Than 30 Days [Member] | Project Business [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Expected credit loss rate | 5.00% | 5.00% | 5.00% |
Less Than 30 Days [Member] | Project Business [Member] | Loss allowance [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Less: Loss allowance | $ (3) |  | $ (5) |
Less Than 30 Days [Member] | Project Business [Member] | Gross carrying amount [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | 64 |  | 78 |
Less Than 30 Days [Member] | Project Business [Member] | Amortized Cost [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | $ 61 |  | $ 73 |
31-60 Days [Member] | Telecommunications Business [Member] | Bottom of Range [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Expected credit loss rate | 3.00% | 3.00% | 0.00% |
31-60 Days [Member] | Telecommunications Business [Member] | Top of Range [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Expected credit loss rate | 68.00% | 68.00% | 68.00% |
31-60 Days [Member] | Telecommunications Business [Member] | Loss allowance [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Less: Loss allowance | $ (24) |  | $ (28) |
31-60 Days [Member] | Telecommunications Business [Member] | Gross carrying amount [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | 51 |  | 75 |
31-60 Days [Member] | Telecommunications Business [Member] | Amortized Cost [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | $ 27 |  | $ 47 |
31-60 Days [Member] | Project Business [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Expected credit loss rate | 10.00% | 10.00% | 10.00% |
31-60 Days [Member] | Project Business [Member] | Loss allowance [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Less: Loss allowance | $ (3) |  | $ (5) |
31-60 Days [Member] | Project Business [Member] | Gross carrying amount [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | 27 |  | 52 |
31-60 Days [Member] | Project Business [Member] | Amortized Cost [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | $ 24 |  | $ 47 |
61-90 Days [Member] | Telecommunications Business [Member] | Bottom of Range [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Expected credit loss rate | 11.00% | 11.00% | 0.00% |
61-90 Days [Member] | Telecommunications Business [Member] | Top of Range [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Expected credit loss rate | 83.00% | 83.00% | 83.00% |
61-90 Days [Member] | Telecommunications Business [Member] | Loss allowance [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Less: Loss allowance | $ (25) |  | $ (35) |
61-90 Days [Member] | Telecommunications Business [Member] | Gross carrying amount [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | 31 |  | 47 |
61-90 Days [Member] | Telecommunications Business [Member] | Amortized Cost [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | $ 6 |  | $ 12 |
61-90 Days [Member] | Project Business [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Expected credit loss rate | 30.00% | 30.00% | 30.00% |
61-90 Days [Member] | Project Business [Member] | Loss allowance [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Less: Loss allowance | $ (3) |  | $ (11) |
61-90 Days [Member] | Project Business [Member] | Gross carrying amount [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | 9 |  | 30 |
61-90 Days [Member] | Project Business [Member] | Amortized Cost [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | $ 6 |  | $ 19 |
91-120 Days [Member] | Telecommunications Business [Member] | Bottom of Range [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Expected credit loss rate | 28.00% | 28.00% | 11.00% |
91-120 Days [Member] | Telecommunications Business [Member] | Top of Range [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Expected credit loss rate | 90.00% | 90.00% | 90.00% |
91-120 Days [Member] | Telecommunications Business [Member] | Loss allowance [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Less: Loss allowance | $ (24) |  | $ (26) |
91-120 Days [Member] | Telecommunications Business [Member] | Gross carrying amount [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | 30 |  | 41 |
91-120 Days [Member] | Telecommunications Business [Member] | Amortized Cost [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | $ 6 |  | $ 15 |
91-120 Days [Member] | Project Business [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Expected credit loss rate | 50.00% | 50.00% | 50.00% |
91-120 Days [Member] | Project Business [Member] | Loss allowance [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Less: Loss allowance | $ (1) |  | $ (5) |
91-120 Days [Member] | Project Business [Member] | Gross carrying amount [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | 2 |  | 12 |
91-120 Days [Member] | Project Business [Member] | Amortized Cost [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | $ 1 |  | $ 7 |
121-180 Days [Member] | Telecommunications Business [Member] | Bottom of Range [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Expected credit loss rate | 52.00% | 52.00% | 17.00% |
121-180 Days [Member] | Telecommunications Business [Member] | Top of Range [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Expected credit loss rate | 96.00% | 96.00% | 96.00% |
121-180 Days [Member] | Telecommunications Business [Member] | Loss allowance [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Less: Loss allowance | $ (21) |  | $ (27) |
121-180 Days [Member] | Telecommunications Business [Member] | Gross carrying amount [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | 25 |  | 28 |
121-180 Days [Member] | Telecommunications Business [Member] | Amortized Cost [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | $ 4 |  | $ 1 |
121-180 Days [Member] | Project Business [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Expected credit loss rate | 80.00% | 80.00% | 80.00% |
121-180 Days [Member] | Project Business [Member] | Loss allowance [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Less: Loss allowance | $ (2) |  | $ (1) |
121-180 Days [Member] | Project Business [Member] | Gross carrying amount [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | 3 |  | 1 |
121-180 Days [Member] | Project Business [Member] | Amortized Cost [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | $ 1 |  | $ 0 |
Over 180 Days [Member] | Telecommunications Business [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Expected credit loss rate | 100.00% | 100.00% | 100.00% |
Over 180 Days [Member] | Telecommunications Business [Member] | Loss allowance [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Less: Loss allowance | $ (626) |  | $ (601) |
Over 180 Days [Member] | Telecommunications Business [Member] | Gross carrying amount [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | 626 |  | 601 |
Over 180 Days [Member] | Telecommunications Business [Member] | Amortized Cost [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | $ 0 |  | $ 0 |
Over 180 Days [Member] | Project Business [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Expected credit loss rate | 100.00% | 100.00% | 100.00% |
Over 180 Days [Member] | Project Business [Member] | Loss allowance [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Less: Loss allowance | $ (1,288) |  | $ (1,472) |
Over 180 Days [Member] | Project Business [Member] | Gross carrying amount [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | 1,288 |  | 1,472 |
Over 180 Days [Member] | Project Business [Member] | Amortized Cost [Member] |  |  |  |
Disclosure of financial assets that are either past due or impaired [Line Items] |  |  |  |
Trade notes and accounts receivable | $ 0 |  | $ 0 |

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