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Cash Generated from Operations - Summary of Cash Flows from Operating Activities (Detail) - KRW (₩) ₩ in Millions | 12 Months Ended
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Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Cash flows from (used in) operating activities [abstract] |  |  |
Profit for the year | ₩ 1,459,395 | ₩ 746,256 | ₩ 695,868
Adjustments to reconcile net income |  |  |
Income tax expense | 519,016 | 285,349 | 320,060
Interest income | (300,900) | (291,425) | (303,722)
Interest expense | 268,847 | 265,035 | 278,975
Dividends income | (21,525) | (4,442) | (3,408)
Depreciation | 2,643,894 | 2,635,307 | 2,567,754
Amortization of intangible assets | 604,744 | 628,154 | 660,705
Depreciation of right-of-use assets | 398,716 | 404,174 | 433,199
Provision for severance benefits | 253,491 | 255,615 | 256,525
Impairment losses on trade receivables | 105,344 | 139,957 | 60,193
Share of net profit or loss of associates and joint ventures | (116,061) | (18,041) | 3,252
Loss(gain) on disposal of associates and joint ventures | 1 | 111 | 30
Loss on the disposal of subsidiaries | 13,483 |  |
Loss(gain) on disposal of right-of-use assets | 8,319 | 2,047 | 1,556
Impairment losses on assets held for sale | 11 | 0 | 7,586
Loss on disposal of property and equipment and investment in properties | 17,410 | 55,590 | 49,284
Loss(gain) on disposal of intangible assets | 2,159 | 246 | (1,248)
Loss on impairment of intangible assets | 3,747 | 211,637 | 61,899
Loss(gain) on foreign currency translation | 180,921 | (138,011) | 75,998
Loss(gain) on valuation and settlement of derivatives, net | (235,130) | 155,600 | (70,482)
Loss(gain) on disposal of financial assets at fair value through profit or loss | (29,974) | 329 | (5,115)
Gain on valuation of financial assets at fair value through profit or loss | (64,660) | (59,044) | (4,335)
Loss(gain) on disposal of financial assets at amortized cost | (35) | (138) | 43
Others | 86,740 | 127,948 | 143,500
Change in operating assets and liabilities, net of effects from purchase of controlled entity and sale of engineering division |  |  |
Decrease(increase) in trade receivables | 327,031 | 66,462 | (433,292)
Decrease(increase) in other receivables | (328,610) | 685,209 | (79,130)
Decrease(increase) in other current assets | (89,230) | 9,089 | 984
Decrease(increase) in other non-current assets | (143,087) | (86,039) | (178,180)
Decrease(increase) in inventories | 32,798 | 288,507 | 240,488
Increase(decrease) in trade payables | 289,044 | (135,760) | 44,354
Decrease in other payables | 207,583 | (1,232,646) | (102,375)
Increase in other current liabilities | 107,993 | 127,076 | 43,384
Increase(decrease) in other non-current liabilities | (14,915) | (56,319) | (199,547)
Decrease(Increase) in provisions | (4,668) | 2,264 | (12,164)
Decrease(Increase) in deferred revenue | 3,696 | (1,948) | 641
Increase in plan assets | (114,631) | (136,336) | (375,499)
Payment of severance benefits | (241,350) | (186,520) | (119,716)
Cash generated from operations (1+2+3) | ₩ 5,829,607 | ₩ 4,745,293 | ₩ 4,058,065

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- Definition Gain on disposal of right-of-use assets. + References No definition available. + Details
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Namespace Prefix: | kt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Impairment losses on current assets held for sale. + References No definition available. + Details
Name: | kt_ImpairmentLossesOnCurrentAssetsHeldForSale
Namespace Prefix: | kt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Loss on the disposal of subsidiaries + References No definition available. + Details
Name: | kt_LossOnTheDisposalOfSubsidiaries
Namespace Prefix: | kt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration