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Financial Risk Management - Summary of Debt-to-equity Ratios (Detail) - KRW (₩) ₩ in Millions | 12 Months Ended |  |  |  |
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Dec. 31, 2018 | Dec. 31, 2017 | Jan. 01, 2018 | Jan. 01, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Disclosure of detailed information about financial instruments [abstract] |  |  |  |  |  |
Total liabilities | ₩ 17,815,630 | ₩ 16,712,367 | ₩ 17,062,496 | ₩ 17,897,638 |  |
Total equity | ₩ 14,658,490 | ₩ 13,183,354 | ₩ 14,190,193 | ₩ 12,916,942 | ₩ 12,916,942 | ₩ 12,253,627
Debt-to-equity ratio | 122.00% | 127.00% |  |  |  |

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