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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, 2018 | Dec. 31, 2017 | Dec. 31, 2016
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Disclosure of maturity analysis for derivative financial liabilities [Line Items] |  |  |
Outflow | ₩ 2,439,559 | ₩ 1,711,595 | ₩ 2,886,867
Inflow | 2,496,356 | 1,686,804 | 3,196,870
Less than 1 year [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [Line Items] |  |  |
Outflow | 455,343 | 638,171 | 1,174,147
Inflow | 484,505 | 608,270 | 1,302,112
1-5 years [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [Line Items] |  |  |
Outflow | 1,466,915 | 546,791 | 1,176,715
Inflow | 1,492,718 | 568,976 | 1,306,199
More than 5 years [member] |  |  |
Disclosure of maturity analysis for derivative financial liabilities [Line Items] |  |  |
Outflow | 517,301 | 526,633 | 536,005
Inflow | ₩ 519,133 | ₩ 509,558 | ₩ 588,559

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