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Fair Value - Summary of Changes in Level 3 of Fair Value Hierarchy for Recurring Fair Value Measurements (Detail) - KRW (₩) ₩ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016
Disclosure of detailed information about financial instruments [Line Items] |  |
Beginning balance | ₩ 30,664,298 |
Ending balance | 29,745,439 | ₩ 30,664,298
Beginning balance | 17,881,580 |
Ending balance | 16,696,309 | 17,881,580
Recurring fair value measurement [Member] | Financial assets at fair value through profit or loss [member] | Level 3 [Member] |  |
Disclosure of detailed information about financial instruments [Line Items] |  |
Beginning balance | 6,277 | 18
Purchases |  | 13,461
Amount recognized in profit or loss | (464) | (7,184)
Sales |  | (18)
Ending balance | 5,813 | 6,277
Recurring fair value measurement [Member] | Available-for-sale [member] | Level 3 [Member] |  |
Disclosure of detailed information about financial instruments [Line Items] |  |
Beginning balance | 287,889 | 267,337
Reclassification | (277) | 5,723
Amount recognized in other comprehensive income | 58,450 | 15,099
Purchases | 85,287 | 1,561
Amount recognized in profit or loss | (113) | (426)
Sales | (124,159) | (1,405)
Ending balance | 307,077 | 287,889
Recurring fair value measurement [Member] | Other derivative liabilities [Member] | Level 3 [Member] |  |
Disclosure of detailed information about financial instruments [Line Items] |  |
Beginning balance | 1,973 | 2,006
Reclassification | 0 | 0
Purchases | 0 | 0
Amount recognized in profit or loss | 3,078 | (33)
Sales | 0 | 0
Ending balance | 5,051 | ₩ 1,973
Recurring fair value measurement [Member] | Derivative financial liabilities [member] | Level 3 [Member] |  |
Disclosure of detailed information about financial instruments [Line Items] |  |
Reclassification | 0 |
Amount recognized in other comprehensive income | (1,909) |
Purchases | 0 |
Amount recognized in profit or loss | 19,634 |
Sales | 0 |
Ending balance | ₩ 17,725 |

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