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Financial Risk Management - Summary of Cash Outflow and Inflow of Derivatives Settled Gross or Net are Undiscounted Contractual Cash Flow (Detail) - KRW (₩) ₩ in Millions | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
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Disclosure of maturity analysis for derivative financial liabilities [Line Items] |  |  |
Outflow | ₩ 2,925,965 | ₩ 2,760,957 | ₩ 2,439,559
Inflow | 2,804,618 | 2,857,949 | 2,496,356
Less than 1 year [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [Line Items] |  |  |
Outflow | 248,300 | 650,497 | 455,343
Inflow | 249,301 | 684,720 | 484,505
1-5 years [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [Line Items] |  |  |
Outflow | 2,179,046 | 1,602,513 | 1,466,915
Inflow | 2,074,747 | 1,648,746 | 1,492,718
More than 5 years [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [Line Items] |  |  |
Outflow | 498,619 | 507,947 | 517,301
Inflow | ₩ 480,570 | ₩ 524,483 | ₩ 519,133

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