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Related Party Transactions - Summary of Significant Transactions with Related Parties (Detail) - KRW (₩) ₩ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Disclosure of transactions between related parties [line items] |  |  |
Sales | ₩ 18,765 | ₩ 23,416 | ₩ 24,312
Purchases | 18,499 | 19,055 | 128,252
Dividend Income |  |  | 11,146
K-Realty CR-REITs No.1 [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Sales | 2,298 | 1,302 | 2,088
Purchases |  |  | 31,984
Dividend Income |  |  | 8,932
MOS GS Co., Ltd. [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Sales |  |  | 493
Purchases |  |  | 12,023
Dividend Income |  |  | 8
MOS Daegu Co., Ltd. [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Sales |  |  | 229
Purchases |  |  | 8,775
Dividend Income |  |  | 8
MOS Chungcheong Co., Ltd. [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Sales |  |  | 540
Purchases |  |  | 9,159
Dividend Income |  |  | 8
MOS Gangnam Co., Ltd. [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Sales |  |  | 333
Purchases |  |  | 11,549
Dividend Income |  |  | 10
MOS GB Co., Ltd. [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Sales |  |  | 1,378
Purchases |  |  | 16,519
Dividend Income |  |  | 12
MOS BS Co., Ltd. [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Sales |  |  | 324
Purchases |  |  | 11,193
Dividend Income |  |  | 10
MOS Honam Co., Ltd. [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Sales |  |  | 331
Purchases |  |  | 10,499
Dividend Income |  |  | 10
Others [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Sales | 809 |  | 2,888
Purchases | 10,272 |  | 9,547
Dividend Income |  |  | 2,148
K Bank Inc. [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Sales | 15,658 | 17,815 | 15,705
Purchases | ₩ 8,227 | 8,524 | 7,004
NgeneBio [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Sales |  | 1,498 | ₩ 3
Purchases |  | 10,531 |
K-Realty CR-REITs No.10 [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Sales |  | ₩ 2,801 |

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