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Cash Generated from Operations - Summary of Significant Transactions not Affecting Cash Flows (Detail) - KRW (₩) ₩ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Cash flows from (used in) operating activities [abstract] |  |  |
Reclassification of the current portion of borrowings | ₩ 1,229,359 | ₩ 1,030,056 | ₩ 1,149,599
Reclassification of construction-in-progress to property and equipment | 3,011,519 | 2,698,146 | 1,988,014
Reclassification of accounts payable from property and equipment | 22,052 | 685,859 | 122,185
Reclassification of accounts payable from intangible assets | (345,675) | (356,911) | 584,595
Reclassification of payable from defined benefit liability | 72,346 | (19,053) | (31,838)
Reclassification of payable from plan assets | ₩ 66,046 | ₩ (14,298) | ₩ (9,497)

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