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Deferred Income Tax and Income Tax Expense - Summary of Movement in Deferred Income Tax Assets and Liabilities (Detail) - KRW (₩) ₩ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | ₩ 563,729 | ₩ 715,747 |
Statement of operations | (1,771) | (152,102) | ₩ (232,134)
Other comprehensive income | 21,802 | 84 |
Ending | 583,760 | 563,729 | 715,747
Deferred tax derivative liabilities [Member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | (49,188) | (19,155) |
Statement of operations | 49,188 | (33,569) |
Other comprehensive income |  | 3,536 |
Ending |  | (49,188) | (19,155)
Deferred tax liabilities available for sale financial assets [Member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | (31,702) | (29,430) |
Statement of operations | (164) | (10) |
Other comprehensive income | 1,346 | (2,262) |
Ending | (30,520) | (31,702) | (29,430)
Deferred tax liabilities investment in subsidiaries associates and joint ventures [Member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | (50,746) | (50,235) |
Statement of operations | (42,659) | (666) |
Other comprehensive income | (3,245) | 155 |
Ending | (96,650) | (50,746) | (50,235)
Deferred tax liabilities depreciation [Member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | (39,498) | (53,872) |
Statement of operations | 39,498 | 14,374 |
Ending |  | (39,498) | (53,872)
Deferred tax liabilities advanced depreciation provision [Member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | (225,687) | (231,692) |
Statement of operations | (22,905) | 6,005 |
Ending | (248,592) | (225,687) | (231,692)
Deferred tax liabilities deposits for severance benefits [Member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | (307,730) | (251,924) |
Statement of operations | (80,126) | (55,806) |
Ending | (387,856) | (307,730) | (251,924)
Deferred tax liabilities accrued income [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | (2,024) | (1,808) |
Statement of operations | (126) | (216) |
Ending | (2,150) | (2,024) | (1,808)
Deferred tax liabilities reserve for technology and human resource development [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | (747) | (1,216) |
Statement of operations | 433 | 469 |
Ending | (314) | (747) | (1,216)
Other deferred tax liabilities [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | (119,366) | (135,802) |
Statement of operations | 10,617 | 16,436 |
Ending | (108,749) | (119,366) | (135,802)
Deferred tax liabilities [Member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | (826,688) | (775,134) |
Statement of operations | (46,244) | (52,983) |
Other comprehensive income | (1,899) | 1,429 |
Ending | (874,831) | (826,688) | (775,134)
Deferred tax derivative assets [Member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Statement of operations | 34,572 |  |
Other comprehensive income | (9,848) |  |
Ending | 24,724 |  |
Deferred tax assets provision for impairment on trade receivables [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | 110,276 | 136,743 |
Statement of operations | 11,380 | (26,467) |
Ending | 121,656 | 110,276 | 136,743
Deferred tax assets inventory valuation [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | 48 | 56 |
Statement of operations | (48) | (8) |
Ending |  | 48 | 56
Deferred tax assets contribution for construction [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | 18,091 | 19,618 |
Statement of operations | 180 | (1,527) |
Ending | 18,271 | 18,091 | 19,618
Deferred tax assets accrued expenses [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | 80,356 | 64,117 |
Statement of operations | 10,683 | 16,239 |
Ending | 91,039 | 80,356 | 64,117
Deferred Tax Assets Provisions [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | 20,221 | 20,353 |
Statement of operations | 3,858 | (132) |
Ending | 24,079 | 20,221 | 20,353
Deferred tax assets property, plant and equipment [Member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | 232,915 | 239,791 |
Statement of operations | (841) | (6,876) |
Ending | 232,074 | 232,915 | 239,791
Deferred tax assets retirement benefit obligations [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | 372,492 | 331,980 |
Statement of operations | 67,751 | 41,857 |
Other comprehensive income | 26,806 | (1,345) |
Ending | 467,049 | 372,492 | 331,980
Deferred tax assets withholding of facilities expenses [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | 6,910 | 7,360 |
Statement of operations | 472 | (450) |
Ending | 7,382 | 6,910 | 7,360
Deferred tax assets accrued payroll expenses [Member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | 25,915 | 21,634 |
Statement of operations | (10,786) | 4,281 |
Ending | 15,129 | 25,915 | 21,634
Deferred tax assets deduction of installment receivables [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | 13,887 | 10,513 |
Statement of operations | (13,887) | 3,374 |
Ending |  | 13,887 | 10,513
Deferred Tax assets assets retirement obligation [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | 18,086 | 16,974 |
Statement of operations | 2,750 | 1,112 |
Ending | 20,836 | 18,086 | 16,974
Deferred tax assets gain or loss foreign currency translation [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | 67,701 | 43,283 |
Statement of operations | (67,558) | 24,418 |
Ending | 143 | 67,701 | 43,283
Deferred tax assets deferred revenue [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | 26,113 | 43,792 |
Statement of operations | 221 | (17,679) |
Ending | 26,334 | 26,113 | 43,792
Deferred tax assets real-estate sales [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | 3,851 | 2,980 |
Statement of operations | 4,847 | 871 |
Ending | 8,698 | 3,851 | 2,980
Deferred tax assets tax credit carry forwards [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | 199,599 | 212,820 |
Statement of operations | (48,823) | (13,221) |
Ending | 150,776 | 199,599 | 212,820
Deferred tax assets accumulated deficit [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning |  | 107,485 |
Statement of operations |  | (107,485) |
Ending |  |  | 107,485
Deferred tax assets deficit carried over [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Statement of operations | 2,699 |  |
Ending | 2,699 |  |
Other deferred tax assets [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | 193,956 | 211,382 |
Statement of operations | 47,003 | (17,426) |
Other comprehensive income | 6,743 |  |
Ending | 247,702 | 193,956 | 211,382
Deferred tax assets [Member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items] |  |  |
Beginning | 1,390,417 | 1,490,881 |
Statement of operations | 44,473 | (99,119) |
Other comprehensive income | 23,701 | (1,345) |
Ending | ₩ 1,458,591 | ₩ 1,390,417 | ₩ 1,490,881

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