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General Information - Summary of Consolidated Subsidiaries (Detail) - KRW (₩)
₩ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Disclosure of subsidiaries [line items]      
Total assets ₩ 33,662,545 ₩ 34,632,214  
Total liabilities 18,111,112 19,491,530  
Operating revenues 24,440,647 24,899,189 ₩ 23,436,050
Profit (loss) for the year ₩ 746,256 ₩ 695,868 ₩ 719,412
KT Powertel Co., Ltd. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT Powertel Co., Ltd. KT Powertel Co., Ltd. KT Powertel Co., Ltd.
Total assets ₩ 119,694 ₩ 118,052 ₩ 124,064
Type of Business Trunk Radio System (TRS) business    
Total liabilities ₩ 18,833 19,766 28,217
Location Korea    
Operating revenues ₩ 65,897 ₩ 62,846 65,620
Controlling percentage ownership 44.80% 44.80%  
Profit (loss) for the year ₩ 3,809 ₩ 3,085 ₩ (5,545)
Closing month December    
KT Linkus Co., Ltd. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT Linkus Co., Ltd. KT Linkus Co., Ltd. KT Linkus Co., Ltd
Total assets ₩ 58,372 ₩ 70,494 ₩ 54,147
Type of Business Public telephone maintenance    
Total liabilities ₩ 54,022 62,088 44,895
Location Korea    
Operating revenues ₩ 84,519 ₩ 97,892 106,337
Controlling percentage ownership 92.40% 92.40%  
Profit (loss) for the year ₩ (3,212) ₩ (2,258) ₩ 1,216
Closing month December    
KT Submarine Co., Ltd. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT Submarine Co., Ltd. KT Submarine Co., Ltd. KT Submarine Co., Ltd.
Total assets ₩ 116,813 ₩ 120,947 ₩ 130,715
Type of Business Submarine cable construction and maintenance    
Total liabilities ₩ 14,032 18,452 27,530
Location Korea    
Operating revenues ₩ 110,201 ₩ 55,244 61,652
Controlling percentage ownership 39.30% 39.30%  
Profit (loss) for the year ₩ 1,197 ₩ 486 ₩ (4,286)
Closing month December    
KT Telecop Co., Ltd. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT Telecop Co., Ltd. KT Telecop Co., Ltd. KT Telecop Co., Ltd.
Total assets ₩ 318,456 ₩ 279,878 ₩ 272,492
Type of Business Security service    
Total liabilities ₩ 193,737 153,841 140,314
Location Korea    
Operating revenues ₩ 392,489 ₩ 332,063 328,262
Controlling percentage ownership 86.80% 86.80%  
Profit (loss) for the year ₩ 212 ₩ (4,875) ₩ 166
Closing month December    
KT Hitel Co., Ltd. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT Hitel Co., Ltd. KT Hitel Co., Ltd. KT Hitel Co., Ltd.
Total assets ₩ 288,949 ₩ 279,818 ₩ 272,708
Type of Business Data communication    
Total liabilities ₩ 92,599 74,769 66,043
Location Korea    
Operating revenues ₩ 350,231 ₩ 323,065 279,117
Controlling percentage ownership 67.10% 67.10%  
Profit (loss) for the year ₩ 2,080 ₩ 1,426 ₩ 657
Closing month December    
KT service bukbu Co., Ltd. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT Service Bukbu Co., Ltd. KT Service Bukbu Co., Ltd. KT Service Bukbu Co., Ltd.
Total assets ₩ 60,825 ₩ 64,802 ₩ 30,599
Type of Business Opening services of fixed line    
Total liabilities ₩ 56,554 58,984 23,964
Location Korea    
Operating revenues ₩ 217,451 ₩ 219,427 195,961
Controlling percentage ownership 67.30% 67.30%  
Profit (loss) for the year ₩ (871) ₩ (445) ₩ (31)
Closing month December    
KT service nambu Co., Ltd. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT Service Nambu Co., Ltd. KT Service Nambu Co., Ltd. KT Service Nambu Co., Ltd.
Total assets ₩ 58,182 ₩ 63,917 ₩ 37,452
Type of Business Opening services of fixed line    
Total liabilities ₩ 51,460 55,548 27,939
Location Korea    
Operating revenues ₩ 264,776 ₩ 266,148 230,088
Controlling percentage ownership 77.30% 77.30%  
Profit (loss) for the year ₩ (456) ₩ 280 ₩ 160
Closing month December    
KT Commerce Inc. [Member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT Commerce Inc.    
Type of Business B2C, B2B service    
Location Korea    
Controlling percentage ownership 100.00% 100.00%  
Closing month December    
KT Strategic Investment Fund No.2 [Member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT Strategic Investment Fund No.2    
Type of Business Investment fund    
Location Korea    
Controlling percentage ownership 100.00% 100.00%  
Closing month December    
KT Strategic Investment Fund No.3 [Member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT Strategic Investment Fund No.3    
Type of Business Investment fund    
Location Korea    
Controlling percentage ownership 100.00% 100.00%  
Closing month December    
KT Strategic Investment Fund No.4 [Member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT Strategic Investment Fund No.4    
Type of Business Investment fund    
Location Korea    
Controlling percentage ownership 100.00% 100.00%  
Closing month December    
KT Strategic Investment Fund No.5 [Member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT Strategic Investment Fund No.5    
Type of Business Investment fund    
Location Korea    
Controlling percentage ownership 100.00% 100.00%  
Closing month December    
BCVP Strategic Investment Fund Number One [member]      
Disclosure of subsidiaries [line items]      
Subsidiary BC-VP Strategic Investment Fund No.1    
Type of Business Investment fund    
Location Korea    
Controlling percentage ownership 100.00% 100.00%  
Closing month December    
BC Card Co., Ltd. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary BC Card Co., Ltd. BC Card Co., Ltd. BC Card Co., Ltd.1
Total assets ₩ 3,084,398 ₩ 3,912,982 ₩ 3,722,379
Type of Business Credit card business    
Total liabilities ₩ 1,778,751 2,594,232 2,630,536
Location Korea    
Operating revenues ₩ 3,387,640 ₩ 3,553,008 3,551,715
Controlling percentage ownership 69.50% 69.50%  
Profit (loss) for the year ₩ 39,455 ₩ 115,885 ₩ 70,889
Closing month December    
VP Inc. [Member]      
Disclosure of subsidiaries [line items]      
Subsidiary VP Inc.    
Type of Business Payment security service for credit card, others    
Location Korea    
Controlling percentage ownership 50.90% 50.90%  
Closing month December    
H&C Network [member]      
Disclosure of subsidiaries [line items]      
Subsidiary H&C Network H&C Network H&C Network
Total assets ₩ 269,651 ₩ 282,016 ₩ 245,841
Type of Business Call centre for financial sectors    
Total liabilities ₩ 61,365 68,401 63,188
Location Korea    
Operating revenues ₩ 322,690 ₩ 320,701 297,470
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ 2,413 ₩ (1,593) ₩ (15,944)
Closing month December    
BC Card China Co., Ltd. [Member]      
Disclosure of subsidiaries [line items]      
Subsidiary BC Card China Co., Ltd.    
Type of Business Software development and data processing    
Location China    
Controlling percentage ownership 100.00% 100.00%  
Closing month December    
INITECH Co., Ltd. [Member]      
Disclosure of subsidiaries [line items]      
Subsidiary INITECH Co., Ltd.    
Type of Business Internet banking ASP and security solutions    
Location Korea    
Controlling percentage ownership 58.20% 58.20%  
Closing month December    
Smartro Co., Ltd. [Member]      
Disclosure of subsidiaries [line items]      
Subsidiary Smartro Co., Ltd.    
Type of Business VAN (Value Added Network) business    
Location Korea    
Controlling percentage ownership 64.50% 64.50%  
Closing month December    
KTDS Co., Ltd. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KTDS Co., Ltd. KTDS Co., Ltd. KTDS Co., Ltd
Total assets ₩ 183,297 ₩ 158,153 ₩ 148,675
Type of Business System integration and maintenance    
Total liabilities ₩ 133,129 105,462 95,834
Location Korea    
Operating revenues ₩ 499,990 ₩ 428,758 434,302
Controlling percentage ownership 95.50% 95.50%  
Profit (loss) for the year ₩ 10,635 ₩ 9,027 ₩ 8,586
Closing month December    
KT M Hows Co., Ltd. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT M Hows Co., Ltd. KT M Hows Co., Ltd. KT M Hows Co., Ltd.
Total assets ₩ 104,704 ₩ 74,326 ₩ 60,197
Type of Business Mobile marketing    
Total liabilities ₩ 76,315 50,638 42,386
Location Korea    
Operating revenues ₩ 44,860 ₩ 33,443 26,673
Controlling percentage ownership 90.00% 90.00%  
Profit (loss) for the year ₩ 6,935 ₩ 6,771 ₩ 3,691
Closing month December    
KT M&S Co., Ltd. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT M&S Co., Ltd. KT M&S Co., Ltd. KT M&S Co., Ltd.
Total assets ₩ 231,260 ₩ 248,142 ₩ 228,073
Type of Business PCS distribution    
Total liabilities ₩ 197,306 215,777 207,740
Location Korea    
Operating revenues ₩ 661,533 ₩ 813,498 791,652
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ (485) ₩ 12,732 ₩ 11,408
Closing month December    
GENIE Music Corporation K T Music Corporation [member]      
Disclosure of subsidiaries [line items]      
Subsidiary GENIE Music Corporation (KT Music Corporation) GENIE Music Corporation (KT Music Corporation) GENIE Music Corporation (KT Music Corporation)
Total assets ₩ 250,538 ₩ 234,131 ₩ 221,559
Type of Business Online music production and distribution    
Total liabilities ₩ 88,488 80,952 75,827
Location Korea    
Operating revenues ₩ 247,237 ₩ 230,480 171,314
Controlling percentage ownership 36.20% 36.00%  
Profit (loss) for the year ₩ 9,472 ₩ 7,658 ₩ 6,374
Closing month December    
KT MOS Bukbu Co.,Ltd. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT MOS Bukbu Co., Ltd. KT MOS Bukbu Co., Ltd. KT MOS Bukbu Co., Ltd.
Total assets ₩ 32,167 ₩ 33,376 ₩ 14,121
Type of Business Telecommunication facility maintenance    
Total liabilities ₩ 26,070 28,841 10,571
Location Korea    
Operating revenues ₩ 67,975 ₩ 63,761 16,543
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ 1,473 ₩ 353 ₩ (782)
Closing month December    
KTMOS Nambu Co.,Ltd. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT MOS Nambu Co., Ltd. KT MOS Nambu Co., Ltd. KT MOS Nambu Co., Ltd.
Total assets ₩ 33,765 ₩ 34,258 ₩ 14,313
Type of Business Telecommunication facility maintenance    
Total liabilities ₩ 24,947 26,722 8,927
Location Korea    
Operating revenues ₩ 71,259 ₩ 67,300 14,941
Controlling percentage ownership 98.40% 98.40%  
Profit (loss) for the year ₩ 1,639 ₩ 3,099 ₩ (2,418)
Closing month December    
KT Skylife Co., Ltd. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT Skylife Co., Ltd. KT Skylife Co., Ltd. KT Skylife Co., Ltd.1
Total assets ₩ 919,476 ₩ 848,276 ₩ 816,001
Type of Business Satellite broadcasting business    
Total liabilities ₩ 175,039 142,839 149,841
Location Korea    
Operating revenues ₩ 706,631 ₩ 704,996 694,059
Controlling percentage ownership 50.30% 50.30%  
Profit (loss) for the year ₩ 58,190 ₩ 56,008 ₩ 52,010
Closing month December    
Skylife TV Co., Ltd. [Member]      
Disclosure of subsidiaries [line items]      
Subsidiary Skylife TV Co., Ltd.    
Type of Business TV contents provider    
Location Korea    
Controlling percentage ownership 92.60% 92.60%  
Closing month December    
KT Estate Inc. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT Estate Inc. KT Estate Inc. KT Estate Inc.1
Total assets ₩ 1,689,601 ₩ 1,686,000 ₩ 1,695,995
Type of Business Residential building development and supply    
Total liabilities ₩ 325,429 295,706 304,712
Location Korea    
Operating revenues ₩ 365,335 ₩ 485,686 569,269
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ 14,370 ₩ 48,552 ₩ 51,854
Closing month December    
KT AMC Co., Ltd. [Member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT AMC Co., Ltd.    
Type of Business Asset management and consulting services    
Location Korea    
Controlling percentage ownership 100.00% 100.00%  
Closing month December    
NEXR Co., Ltd. [Member]      
Disclosure of subsidiaries [line items]      
Subsidiary NEXR Co., Ltd.    
Type of Business Cloud system implementation    
Location Korea    
Controlling percentage ownership 100.00% 100.00%  
Closing month December    
KTGDH Co., Ltd. (KTSB Data service) [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KTGDH Co., Ltd. (KTSB Data Service) KTGDH Co., Ltd. (KTSB Data service) KTGDH Co., Ltd. (KTSB Data service)
Total assets ₩ 11,003 ₩ 10,437 ₩ 8,632
Type of Business Data centre development and related service    
Total liabilities ₩ 1,669 1,628 523
Location Korea    
Operating revenues ₩ 4,282 ₩ 3,977 4,627
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ 538 ₩ 344 ₩ (9,576)
Closing month December    
KT Sat Co., Ltd. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT Sat Co., Ltd. KT Sat Co., Ltd. KT Sat Co., Ltd.
Total assets ₩ 630,740 ₩ 651,195 ₩ 685,926
Type of Business Satellite communication business    
Total liabilities ₩ 92,791 127,523 173,513
Location Korea    
Operating revenues ₩ 173,693 ₩ 168,376 137,186
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ 14,753 ₩ 16,497 ₩ 4,921
Closing month December    
Nasmedia Co Ltd [member]      
Disclosure of subsidiaries [line items]      
Subsidiary Nasmedia Co., Ltd. Nasmedia Co., Ltd. Nasmedia Co., Ltd.
Total assets ₩ 422,039 ₩ 356,236 ₩ 303,112
Type of Business Solution provider and IPTV advertisement sales business    
Total liabilities ₩ 221,371 203,105 161,164
Location Korea    
Operating revenues ₩ 113,136 ₩ 117,550 106,805
Controlling percentage ownership 44.00% 44.00%  
Profit (loss) for the year ₩ 23,134 ₩ 22,484 20,596
Closing month December    
KT sports [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT Sports Co., Ltd. KT Sports Co., Ltd.  
Total assets     9,560
Type of Business Management of sports group    
Total liabilities     6,376
Operating revenues     55,565
Profit (loss) for the year     ₩ (154)
KT Sports Co Ltd [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT Sports Co., Ltd.   KT Sports Co., Ltd.
Total assets ₩ 26,572 ₩ 15,603  
Total liabilities ₩ 14,940 8,333  
Location Korea    
Operating revenues ₩ 46,608 ₩ 55,241  
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ (2,516) ₩ (464)  
Closing month December    
KT music contents fund no.1 [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT Music Contents Fund No.1 KT Music Contents Fund No.1 KT Music Contents Fund No.1
Total assets ₩ 4,844 ₩ 10,579 ₩ 14,092
Type of Business Music contents investment business    
Total liabilities ₩ 1,525 1,677 1,035
Location Korea    
Operating revenues ₩ 243 ₩ 521 559
Controlling percentage ownership 80.00% 80.00%  
Profit (loss) for the year ₩ 84 ₩ 345 ₩ 294
Closing month December    
K T Music Contents Fund No.2 [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT Music Contents Fund No.2 KT Music Contents Fund No.2 KT Music Contents Fund No.2
Total assets ₩ 15,021 ₩ 7,675 ₩ 7,629
Type of Business Music contents investment business    
Total liabilities ₩ 285 279 281
Location Korea    
Operating revenues ₩ 169 ₩ 331 150
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ (116) ₩ 48 ₩ (142)
Closing month December    
KT-Michigan global content fund [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT-Michigan Global Contents Fund KT-Michigan Global Content Fund KT-Michigan Global Content Fund
Total assets ₩ 10,382 ₩ 11,688 ₩ 12,741
Type of Business Content investment business    
Total liabilities ₩ 175 61 0
Location Korea    
Operating revenues ₩ 111 ₩ 248 869
Controlling percentage ownership 88.60% 88.60%  
Profit (loss) for the year ₩ (1,420) ₩ (1,113) ₩ (670)
Closing month December    
Autopion Co., Ltd. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary Autopion Co., Ltd. Autopion Co., Ltd. Autopion Co., Ltd.
Total assets ₩ 4,903 ₩ 7,460 ₩ 8,838
Type of Business Information and communication service    
Total liabilities ₩ 4,961 4,894 5,801
Location Korea    
Operating revenues ₩ 6,174 ₩ 5,604 12,035
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ (2,459) ₩ (302) ₩ 453
Closing month December    
KTCS Corporation [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KTCS Corporation KTCS Corporation KTCS Corporation
Total assets ₩ 384,919 ₩ 378,171 ₩ 350,280
Type of Business Database and online information provider    
Total liabilities ₩ 215,175 213,983 188,561
Location Korea    
Operating revenues ₩ 933,006 ₩ 944,778 1,019,787
Controlling percentage ownership 31.90% 30.90%  
Profit (loss) for the year ₩ 11,323 ₩ 7,597 ₩ 11,401
Closing month December    
KTIS Corporation [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KTIS Corporation KTIS Corporation KTIS Corporation
Total assets ₩ 294,289 ₩ 305,798 ₩ 229,246
Type of Business Database and online information provider    
Total liabilities ₩ 126,894 137,524 68,997
Location Korea    
Operating revenues ₩ 454,172 ₩ 454,561 451,532
Controlling percentage ownership 30.80% 30.10%  
Profit (loss) for the year ₩ 7,387 ₩ 9,205 ₩ 7,900
Closing month December    
KT M mobile Co., Ltd. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT M Mobile Co., Ltd. KT M mobile Co., Ltd. KT M mobile Co., Ltd.
Total assets ₩ 129,011 ₩ 135,917 ₩ 146,334
Type of Business Special category telecommunications operator and sales of communication device    
Total liabilities ₩ 27,281 30,603 35,335
Location Korea    
Operating revenues ₩ 163,472 ₩ 161,720 172,674
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ (3,617) ₩ (5,580) ₩ (10,085)
Closing month December    
KT Investment Co., Ltd. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT Investment Co., Ltd. KT Investment Co., Ltd. KT Investment Co., Ltd.
Total assets ₩ 115,627 ₩ 73,463 ₩ 74,580
Type of Business Technology business finance    
Total liabilities ₩ 93,695 56,212 58,040
Location Korea    
Operating revenues ₩ 47,801 ₩ 13,375 8,095
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ 4,680 ₩ 847 ₩ 247
Closing month December    
Whowho&Company Co., Ltd. [Member]      
Disclosure of subsidiaries [line items]      
Subsidiary Whowho&Company Co., Ltd.    
Type of Business Software development and supply    
Location Korea    
Controlling percentage ownership 100.00% 100.00%  
Closing month December    
PlayD Co., Ltd. (N Search Marketing Co., Ltd.) [member]      
Disclosure of subsidiaries [line items]      
Subsidiary PlayD Co., Ltd. (N Search Marketing Co., Ltd.)    
Type of Business Advertising agency    
Location Korea    
Controlling percentage ownership 70.40% 100.00%  
Closing month December    
Next Connect PFV [member]      
Disclosure of subsidiaries [line items]      
Subsidiary Next Connect PFV Next connect PFV Next connect PFV
Total assets ₩ 394,268 ₩ 385,412 ₩ 385,769
Type of Business Residential building development and supply    
Total liabilities ₩ 37,271 24,275 34,370
Location Korea    
Operating revenues ₩ 26 ₩ 1,590 143
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ (7,101) ₩ (5,898) ₩ (12,449)
Closing month December    
KT Rwanda Networks Ltd. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT Rwanda Networks Ltd. KT Rwanda Networks Ltd. KT Rwanda Networks Ltd.
Total assets ₩ 114,768 ₩ 132,461 ₩ 144,129
Type of Business Network installation and management    
Total liabilities ₩ 191,781 183,164 162,801
Location Rwanda    
Operating revenues ₩ 17,870 ₩ 18,013 15,150
Controlling percentage ownership 51.00% 51.00%  
Profit (loss) for the year ₩ (34,610) ₩ (31,662) ₩ (29,238)
Closing month December    
AOS Ltd. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary AOS Ltd. AOS Ltd. AOS Ltd.
Total assets ₩ 11,812 ₩ 12,337 ₩ 14,018
Type of Business System integration and maintenance    
Total liabilities ₩ 3,875 3,993 4,952
Location Rwanda    
Operating revenues ₩ 5,719 ₩ 6,982 6,300
Controlling percentage ownership 51.00% 51.00%  
Profit (loss) for the year ₩ 296 ₩ (591) ₩ (680)
Closing month December    
KT Belgium [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT Belgium KT Belgium KT Belgium
Total assets ₩ 87,608 ₩ 93,321 ₩ 90,172
Type of Business Foreign investment business    
Total liabilities   11 1
Location Belgium    
Operating revenues   ₩ (81) 29
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ (81) ₩ (64) ₩ (43)
Closing month December    
KT ORS Belgium [member]      
Disclosure of subsidiaries [line items]      
Subsidiary   KT ORS Belgium KT ORS Belgium
Total assets   ₩ 6,913 ₩ 6,709
Total liabilities   14 5
Profit (loss) for the year   ₩ (43) ₩ (46)
Korea Telecom Japan Co., Ltd. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary Korea Telecom Japan Co., Ltd. Korea Telecom Japan Co., Ltd. Korea Telecom Japan Co., Ltd.
Total assets ₩ 2,694 ₩ 1,851 ₩ 1,326
Type of Business Foreign telecommunication business    
Total liabilities ₩ 2,622 2,858 2,910
Location Japan    
Operating revenues ₩ 1,853 ₩ 2,891 1,965
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ 1 ₩ 651 ₩ (126)
Closing month December    
KBTO sp.zo.o. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KBTO sp.z o.o. KBTO sp.zo.o. KBTO sp.zo.o.
Total assets ₩ 438 ₩ 1,767 ₩ 1,364
Type of Business Electronic communication business    
Total liabilities ₩ 117 245 217
Location Poland    
Operating revenues ₩ 490 ₩ 519 202
Controlling percentage ownership 97.40% 97.20%  
Profit (loss) for the year ₩ (2,823) ₩ (3,457) ₩ (3,771)
Closing month December    
Korea Telecom China Co., Ltd. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary Korea Telecom China Co., Ltd. Korea Telecom China Co., Ltd. Korea Telecom China Co., Ltd.
Total assets ₩ 381 ₩ 879 ₩ 661
Type of Business Foreign telecommunication business    
Total liabilities ₩ 21 39 22
Location China    
Operating revenues ₩ 618 ₩ 844 681
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ (492) ₩ 192 ₩ 10
Closing month December    
KT Dutch B.V. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT Dutch B.V. KT Dutch B.V. KT Dutch B.V.
Total assets ₩ 29,585 ₩ 31,003 ₩ 31,693
Type of Business Super iMax and East Telecom management    
Total liabilities ₩ 10,109 50 41
Location Netherlands    
Operating revenues   ₩ 26,782 191
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ 6,061 ₩ (242) ₩ 105
Closing month December    
Super iMax LLC [member]      
Disclosure of subsidiaries [line items]      
Subsidiary   Super iMax LLC Super iMax LLC
Total assets   ₩ 3,568 ₩ 4,150
Total liabilities   5,304 4,528
Operating revenues   4,604 4,845
Profit (loss) for the year   ₩ (631) ₩ (424)
East Telecom LLC [member]      
Disclosure of subsidiaries [line items]      
Subsidiary East Telecom LLC East Telecom LLC East Telecom LLC1
Total assets   ₩ 20,857 ₩ 16,590
Type of Business Fixed line telecommunication business    
Total liabilities   16,302 14,263
Location Uzbekistan    
Operating revenues   ₩ 17,186 15,087
Controlling percentage ownership 91.60% 91.00%  
Profit (loss) for the year   ₩ 2,140 ₩ 2,639
Closing month December    
Korea Telecom America, Inc. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary Korea Telecom America, Inc. Korea Telecom America, Inc. Korea Telecom America, Inc.
Total assets ₩ 4,498 ₩ 4,611 ₩ 4,218
Type of Business Foreign telecommunication business    
Total liabilities ₩ 125 537 832
Location USA    
Operating revenues ₩ 6,808 ₩ 6,808 7,554
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ 712 ₩ 572 ₩ 350
Closing month December    
PT. KT Indonesia [member]      
Disclosure of subsidiaries [line items]      
Subsidiary   PT. KT Indonesia PT. KT Indonesia
Total assets   ₩ 8 ₩ 8
PT BC card Asia Pacific [member]      
Disclosure of subsidiaries [line items]      
Subsidiary PT. BC Card Asia Pacific    
Type of Business Software development and supply    
Location Indonesia    
Controlling percentage ownership 99.90% 99.90%  
Closing month December    
KT Hongkong Telecommunications Co., Ltd. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT Hong Kong Telecommunications Co., Ltd. KT Hongkong Telecommunications Co., Ltd. KT Hongkong Telecommunications Co., Ltd.
Total assets ₩ 6,159 ₩ 5,126 ₩ 3,616
Type of Business Fixed line communication business    
Total liabilities ₩ 2,800 2,923 2,143
Location Hong Kong    
Operating revenues ₩ 16,386 ₩ 13,321 9,990
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ 1,308 ₩ 586 ₩ 351
Closing month December    
Korea Telecom Singapore Pte.Ltd. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary Korea Telecom Singapore Pte. Ltd.    
Type of Business Foreign investment business    
Location Singapore    
Controlling percentage ownership 100.00% 100.00%  
Closing month December    
Texnoprosistem LLP [member]      
Disclosure of subsidiaries [line items]      
Subsidiary Texnoprosistem LLC    
Type of Business Fixed line internet business    
Location Uzbekistan    
Controlling percentage ownership 100.00% 100.00%  
Closing month December    
Nasmedia Thailand Co Ltd [member]      
Disclosure of subsidiaries [line items]      
Subsidiary Nasmedia Thailand Co., Ltd.    
Type of Business Internet advertising solution provider    
Location Thailand    
Controlling percentage ownership 99.90% 99.90%  
Closing month December    
KT Huimangjieum [member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT Huimangjieum KT Huimangjieum  
Total assets ₩ 3,720 ₩ 2,129  
Type of Business Manufacturing    
Total liabilities ₩ 2,787 1,019  
Location Korea    
Operating revenues ₩ 5,239 ₩ 1,027  
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ (13) ₩ (390)  
Closing month December    
GE Premier 1st Corporate Restructuring Real Estate Investment Trust Co. [member]      
Disclosure of subsidiaries [line items]      
Subsidiary GE Premier 1st Corporate Restructuring Real Estate Investment Trust Co. GE Premier 1st Corporate Restructuring Real Estate Investment Trust Co.  
Total assets ₩ 5,703 ₩ 6,285  
Type of Business Residential building investment and rent    
Total liabilities ₩ 1,165 1,139  
Location Korea    
Operating revenues ₩ 333 ₩ 176  
Controlling percentage ownership 68.10% 63.50%  
Profit (loss) for the year ₩ 83 ₩ 70  
Closing month December    
K-REALTY RENTAL HOUSING REIT 3 [member]      
Disclosure of subsidiaries [line items]      
Subsidiary K-REALTY RENTAL HOUSING REIT 3 K-REALTY RENTAL HOUSING REIT 3  
Total assets   ₩ 300  
Type of Business Residential building    
Location Korea    
Controlling percentage ownership 88.60% 100.00%  
Closing month December    
GENIE Music Corporation(KT Music Corporation) [member]      
Disclosure of subsidiaries [line items]      
Subsidiary GENIE Music Corporation (KT Music Corporation)    
Storywiz Co Ltd [Member]      
Disclosure of subsidiaries [line items]      
Subsidiary Storywiz Co., Ltd    
Total assets ₩ 21,594    
Type of Business Content and software development and supply    
Total liabilities ₩ 10,065    
Location Korea    
Operating revenues ₩ 19,209    
Controlling percentage ownership 100.00%    
Profit (loss) for the year ₩ (1,954)    
Closing month December    
KT Engineering Co Ltd KT ENGCORE Co Ltd [Member]      
Disclosure of subsidiaries [line items]      
Subsidiary KT Engineering Co., Ltd. (KT ENGCORE Co., Ltd.)    
Total assets ₩ 138,220    
Type of Business Telecommunication facility construction and maintenance    
Total liabilities ₩ 102,963    
Location Korea    
Operating revenues ₩ 346,040    
Controlling percentage ownership 100.00%    
Profit (loss) for the year ₩ (8,461)    
Closing month December