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General Information - Summary of Consolidated Subsidiaries (Detail) - KRW (₩)
₩ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure of subsidiaries [Line Items]      
Total assets ₩ 29,745,439 ₩ 30,664,298  
Total liabilities 16,696,309 17,881,580  
Operating revenues 23,546,929 23,120,878 ₩ 22,699,856
Profit (loss) for the year ₩ 546,341 ₩ 795,117 ₩ 624,685
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 ₩ 115,125 ₩ 113,725 ₩ 113,515
Type of Business Trunk radio system business    
Total liabilities ₩ 18,937 19,899 21,182
Location Korea    
Operating revenues ₩ 69,234 ₩ 81,390 104,527
Controlling percentage ownership 44.80% 44.80%  
Profit (loss) for the year ₩ 2,112 ₩ 202 ₩ (32,417)
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 ₩ 59,344 ₩ 64,318 ₩ 77,141
Type of Business Public telephone maintenance    
Total liabilities ₩ 51,516 56,953 65,745
Location Korea    
Operating revenues ₩ 112,043 ₩ 117,587 116,095
Controlling percentage ownership 91.40% 91.40%  
Profit (loss) for the year ₩ 725 ₩ (3,830) ₩ 3,449
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 ₩ 142,797 ₩ 156,993 ₩ 160,314
Type of Business Submarine cable construction and maintenance    
Total liabilities ₩ 34,056 55,573 63,518
Location Korea    
Operating revenues ₩ 73,985 ₩ 84,137 67,268
Controlling percentage ownership 39.30% 39.30%  
Profit (loss) for the year ₩ 8,243 ₩ 5,146 ₩ 4,145
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 ₩ 264,353 ₩ 265,553 ₩ 269,191
Type of Business Security service    
Total liabilities ₩ 131,633 132,344 134,966
Location Korea    
Operating revenues ₩ 317,591 ₩ 315,948 302,844
Controlling percentage ownership 86.80% 86.80%  
Profit (loss) for the year ₩ 2,885 ₩ 143 ₩ (7,593)
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 ₩ 258,240 ₩ 249,202 ₩ 235,757
Type of Business Data communication    
Total liabilities ₩ 52,943 46,941 33,938
Location Korea    
Operating revenues ₩ 227,884 ₩ 198,994 162,155
Controlling percentage ownership 67.10% 67.10%  
Profit (loss) for the year ₩ 3,225 ₩ 4,298 ₩ 7,258
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., Ltd2
Total assets ₩ 29,281 ₩ 32,863 ₩ 31,879
Type of Business Opening services of fixed line    
Total liabilities ₩ 22,096 24,580 22,627
Location Korea    
Operating revenues ₩ 194,837 ₩ 182,952 89,498
Controlling percentage ownership 67.30% 67.30%  
Profit (loss) for the year ₩ 688 ₩ 694 ₩ (4,630)
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., Ltd2
Total assets ₩ 36,076 ₩ 32,621 ₩ 20,729
Type of Business Opening services of fixed line    
Total liabilities ₩ 26,412 24,282 10,567
Location Korea    
Operating revenues ₩ 232,996 ₩ 218,602 110,129
Controlling percentage ownership 77.30% 77.30%  
Profit (loss) for the year ₩ 875 ₩ 772 ₩ (5,055)
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 New Business Fund No.1 [Member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary KT New Business Fund No.    
Type of Business Investment fund    
Location Korea    
Controlling percentage ownership 100.00% 100.00%  
Closing month December    
KT Strategic Investment Fund No.1 [Member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary KT Strategic Investment Fund No.1    
Type of Business Investment fund    
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 number four [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%    
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 ₩ 4,048,263 ₩ 3,651,065 ₩ 2,963,952
Type of Business Credit card business    
Total liabilities ₩ 2,955,038 2,602,404 1,945,634
Location Korea    
Operating revenues ₩ 3,628,995 ₩ 3,567,512 3,504,946
Controlling percentage ownership 69.50% 69.50%  
Profit (loss) for the year ₩ 156,109 ₩ 163,131 ₩ 218,969
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 ₩ 273,856 ₩ 272,110 ₩ 248,189
Type of Business Call centre for financial sectors    
Total liabilities ₩ 65,446 80,983 70,635
Location Korea    
Operating revenues ₩ 277,622 ₩ 266,613 241,008
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ 16,104 ₩ 14,749 ₩ 19,513
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.4    
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 81.10% 81.10%  
Closing month December    
KTDS Co., Ltd. [member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary KTDS Co., Ltd. KTDS Co., Ltd. KTDS Co., Ltd.
Total assets ₩ 144,922 ₩ 197,970 ₩ 162,518
Type of Business System integration and maintenance    
Total liabilities ₩ 93,343 151,644 116,654
Location Korea    
Operating revenues ₩ 459,266 ₩ 476,379 423,015
Controlling percentage ownership 95.50% 95.50%  
Profit (loss) for the year ₩ 11,584 ₩ 10,838 ₩ 12,836
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 ₩ 42,738 ₩ 28,539 ₩ 25,093
Type of Business Mobile marketing    
Total liabilities ₩ 28,489 18,466 17,980
Location Korea    
Operating revenues ₩ 24,610 ₩ 19,922 19,352
Controlling percentage ownership 90.00% 90.00%  
Profit (loss) for the year ₩ 4,097 ₩ 2,865 ₩ 1,728
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 ₩ 242,388 ₩ 247,854 ₩ 256,246
Type of Business PCS distribution    
Total liabilities ₩ 231,151 227,507 217,892
Location Korea    
Operating revenues ₩ 734,420 ₩ 724,144 853,011
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ (9,707) ₩ (12,955) ₩ (18,776)
Closing month December    
G E N I E Music Corporation K T Music Corporation [member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary GENIE Music Corporation(KT Music Corporation)    
Type of Business Online music production and distribution    
Location Korea    
Controlling percentage ownership 42.50% 49.90%  
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.
Total assets ₩ 792,893 ₩ 777,948 ₩ 711,294
Type of Business Satellite broadcasting business    
Total liabilities ₩ 210,550 231,452 217,850
Location Korea    
Operating revenues ₩ 687,752 ₩ 668,945 668,521
Controlling percentage ownership 50.30% 50.30%  
Profit (loss) for the year ₩ 57,314 ₩ 68,863 ₩ 72,987
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.
Total assets ₩ 1,869,194 ₩ 1,734,729 ₩ 1,603,438
Type of Business Residential building development and supply    
Total liabilities ₩ 502,915 375,341 260,292
Location Korea    
Operating revenues ₩ 428,446 ₩ 405,417 254,776
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ 52,416 ₩ 46,815 ₩ 27,487
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    
KTSB Data service [member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary KTSB Data service KTSB Data service KTSB Data service
Total assets ₩ 18,306 ₩ 20,075 ₩ 23,063
Type of Business Data centre development and related service    
Total liabilities ₩ 605 759 1,730
Location Korea    
Operating revenues ₩ 4,950 ₩ 5,136 4,390
Controlling percentage ownership 51.00% 51.00%  
Profit (loss) for the year ₩ (1,651) ₩ (1,983) ₩ (2,444)
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 ₩ 742,391 ₩ 744,653 ₩ 679,959
Type of Business Satellite communication business    
Total liabilities ₩ 220,804 253,041 210,110
Location Korea    
Operating revenues ₩ 147,649 ₩ 144,594 133,326
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ 29,601 ₩ 36,266 ₩ 27,174
Closing month December    
K T Innoedu Co [member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary KT Innoedu Co   KT Innoedu Co., Ltd.
Total assets     ₩ 5,858
Type of Business E-learning business    
Total liabilities     7,585
Location Korea    
Operating revenues     18,156
Controlling percentage ownership   96.80%  
Profit (loss) for the year     ₩ (4,288)
Closing month December    
Nasmedia, Inc. [member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary Nasmedia, Inc. Nasmedia, Inc. Nasmedia, Inc.
Total assets ₩ 315,967 ₩ 263,925 ₩ 141,733
Type of Business Online advertisement    
Total liabilities ₩ 188,197 159,502 72,202
Location Korea    
Operating revenues ₩ 120,667 ₩ 70,037 45,630
Controlling percentage ownership 42.80% 42.80%  
Profit (loss) for the year ₩ 26,676 ₩ 11,972 ₩ 9,916
Closing month December    
KT sports [member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary KT Sports KT Sports KT Sports
Total assets ₩ 11,131 ₩ 16,925 ₩ 15,341
Type of Business Management of sports group    
Total liabilities ₩ 7,805 13,573 11,643
Location Korea    
Operating revenues ₩ 53,357 ₩ 48,476 51,801
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ (199) ₩ (198) ₩ (3,836)
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 ₩ 13,804 ₩ 10,592 ₩ 10,206
Type of Business Music contents investment business    
Total liabilities ₩ 1,041 331 47
Location Korea    
Operating revenues ₩ 370 ₩ 349 468
Controlling percentage ownership 80.00% 80.00%  
Profit (loss) for the year ₩ (499) ₩ 103 ₩ (111)
Closing month December    
K T Music Contents Fund No.2 [member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary KT Music Contents Fund No.2    
Type of Business Music contents investment business    
Location Korea    
Controlling percentage ownership 100.00%    
Closing month December    
KT-Michigan global content fund [member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary KT-Michigan Global Content Fund KT-Michigan Global Content Fund KT-Michigan Global Content Fund
Total assets ₩ 14,575 ₩ 16,250 ₩ 5,401
Type of Business Content investment business    
Total liabilities ₩ 147 163  
Location Korea    
Operating revenues ₩ 159 ₩ 133 861
Controlling percentage ownership 88.60% 88.60%  
Profit (loss) for the year ₩ (426) ₩ (514) ₩ (209)
Closing month December    
Autopion Co., Ltd. [member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary Autopion Co., Ltd. Autopion Co., Ltd. Autopion Co., Ltd.
Total assets ₩ 6,306 ₩ 6,163 ₩ 7,102
Type of Business Service for information and communication    
Total liabilities ₩ 3,530 2,794 3,317
Location Korea    
Operating revenues ₩ 6,679 ₩ 7,772 10,585
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ (618) ₩ (409) ₩ 1,123
Closing month December    
KTCS Corporation [member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary KTCS Corporation KTCS Corporation KTCS Corporation
Total assets ₩ 348,334 ₩ 322,768 ₩ 346,949
Type of Business Database and online information provider    
Total liabilities ₩ 188,764 166,642 194,367
Location Korea    
Operating revenues ₩ 968,186 ₩ 955,050 1,066,556
Controlling percentage ownership 30.90% 30.90%  
Profit (loss) for the year ₩ 7,385 ₩ 7,892 ₩ 13,685
Closing month December    
KTIS Corporation [member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary KTIS Corporation KTIS Corporation KTIS Corporation
Total assets ₩ 223,818 ₩ 221,176 ₩ 211,164
Type of Business Database and online information provider    
Total liabilities ₩ 62,569 63,871 55,370
Location Korea    
Operating revenues ₩ 438,597 ₩ 436,914 473,892
Controlling percentage ownership 30.10% 30.10%  
Profit (loss) for the year ₩ 8,337 ₩ 9,991 ₩ 15,041
Closing month December    
KT M mobile [member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary KT M mobile KT M mobile KT M mobile
Total assets ₩ 93,601 ₩ 131,446 ₩ 64,756
Type of Business Special category telecommunications operator and sales of communication device    
Total liabilities ₩ 21,453 20,369 13,121
Location Korea    
Operating revenues ₩ 159,684 ₩ 112,532 42,478
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ (38,883) ₩ (40,041) ₩ (36,725)
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 ₩ 54,673 ₩ 39,506 ₩ 49,485
Type of Business Technology business finance    
Total liabilities ₩ 38,313 23,123 30,827
Location Korea    
Operating revenues ₩ 8,794 ₩ 10,130 4,704
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ (619) ₩ (1,832) ₩ (219)
Closing month December    
Ngen bio [member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary NgenBio    
Type of Business Medicine and Pharmacy development business    
Location Belgium    
Controlling percentage ownership   49.80%  
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 business    
Location Korea    
Controlling percentage ownership 100.00% 100.00%  
Closing month December    
KT Rwanda Networks Ltd. [member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary KT Rwanda Networks Ltd. KT Rwanda Networks Ltd. Olleh Rwanda Networks Ltd.
Total assets ₩ 151,359 ₩ 167,112 ₩ 188,951
Type of Business Network installation and management    
Total liabilities ₩ 139,561 138,651 147,653
Location Rwanda    
Operating revenues ₩ 15,931 ₩ 13,435 7,299
Controlling percentage ownership 51.00% 51.00%  
Profit (loss) for the year ₩ (22,762) ₩ (31,455) ₩ (28,721)
Closing month December    
AOS Ltd. [member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary AOS Ltd. AOS Ltd. Africa Olleh Services Ltd.
Total assets ₩ 9,437 ₩ 10,025 ₩ 11,928
Type of Business System integration and maintenance    
Total liabilities ₩ 4,519 3,179 12,187
Location Rwanda    
Operating revenues ₩ 8,952 ₩ 14,481 8,712
Controlling percentage ownership 51.00% 51.00%  
Profit (loss) for the year ₩ (682) ₩ (1,123) ₩ (923)
Closing month December    
KT Belgium [member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary KT Belgium KT Belguium KT Belgium
Total assets ₩ 86,455 ₩ 79,391 ₩ 77,058
Type of Business Foreign investment business    
Total liabilities ₩ 8 ₩ 7 4
Location Belgium    
Operating revenues ₩ 49    
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ (2) ₩ (67) ₩ (127)
Closing month December    
KT ORS Belgium [member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary KT ORS Belgium KT ORS Belgium KT ORS Belgium
Total assets ₩ 1,769 ₩ 2,013 ₩ 1,996
Type of Business Foreign investment business    
Total liabilities ₩ 14 ₩ 23 20
Location Belgium    
Operating revenues ₩ 10    
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ (10) ₩ (46) ₩ (75)
Closing month December    
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 ₩ 1,554 ₩ 3,592 ₩ 13,889
Type of Business Foreign telecommunication business    
Total liabilities ₩ 2,788 5,374 14,393
Location Japan    
Operating revenues ₩ 2,772 ₩ 5,122 25,652
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ 536 ₩ (1,391) ₩ (248)
Closing month December    
KBTO sp.zo.o. [member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary KBTO sp.zo.o. KBTO sp.zo.o. KBTO sp.zo.o.
Total assets ₩ 3,311 ₩ 1,166 ₩ 1,471
Type of Business Electronic communication business    
Total liabilities ₩ 2,268 2,378 1,817
Location Poland    
Operating revenues ₩ 67 ₩ 21  
Controlling percentage ownership 94.00% 75.00%  
Profit (loss) for the year ₩ (3,456) ₩ (2,587) ₩ (328)
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 ₩ 665 ₩ 532 ₩ 909
Type of Business Foreign telecommunication business    
Total liabilities ₩ 32 188 198
Location China    
Operating revenues ₩ 1,030 ₩ 930 1,748
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ 348 ₩ 60 ₩ (95)
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 ₩ 30,312 ₩ 34,197 ₩ 29,402
Type of Business Super iMax and East Telecom management    
Total liabilities ₩ 50 73 27
Location Netherlands    
Operating revenues ₩ 206 ₩ 166 161
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ 169 ₩ 85 ₩ 118
Closing month December    
Super iMax LLC [member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary Super iMax LLC Super iMax LLC Super iMax LLC
Total assets ₩ 3,449 ₩ 10,308 ₩ 14,962
Type of Business Wireless high speed internet business    
Total liabilities ₩ 4,886 6,734 8,186
Location Uzbekistan    
Operating revenues ₩ 7,314 ₩ 10,759 8,291
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ (4,584) ₩ (1,802) ₩ (2,220)
Closing month December    
East Telecom LLC [member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary East Telecom LLC East Telecom LLC East Telecom LLC
Total assets ₩ 11,672 ₩ 31,885 ₩ 30,833
Type of Business Fixed line telecommunication business    
Total liabilities ₩ 11,748 16,554 17,066
Location Uzbekistan    
Operating revenues ₩ 19,663 ₩ 27,492 24,066
Controlling percentage ownership 91.00% 91.00%  
Profit (loss) for the year ₩ (9,118) ₩ 3,257 ₩ 664
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 ₩ 3,694 ₩ 4,464 ₩ 6,016
Type of Business Foreign telecommunication business    
Total liabilities ₩ 791 1,306 1,378
Location USA    
Operating revenues ₩ 6,783 ₩ 7,113 6,391
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ 109 ₩ 181 ₩ 156
Closing month December    
PT. KT Indonesia [member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary PT. KT Indonesia PT. KT Indonesia PT. KT Indonesia
Total assets ₩ 8 ₩ 16 ₩ 22
Type of Business Foreign telecommunication business    
Location Indonesia    
Controlling percentage ownership 99.00% 99.00%  
Profit (loss) for the year ₩ (6) ₩ (7) ₩ (9)
Closing month December    
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 Hongkong Telecommunications Co., Ltd. KT Hongkong Telecommunications Co., Ltd.  
Total assets ₩ 2,578 ₩ 1,571  
Type of Business Fixed line communication business    
Total liabilities ₩ 1,497 956  
Location Hong Kong    
Operating revenues ₩ 7,304 ₩ 1,568  
Controlling percentage ownership 100.00% 100.00%  
Profit (loss) for the year ₩ 494 ₩ 120  
Closing month December    
KT Hong kong Limited [member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary KT Hong kong Limited    
Type of Business Foreign investment business    
Location Hong Kong    
Controlling percentage ownership 100.00% 100.00%  
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 LLP.    
Type of Business Fixed line internet business    
Location Uzbekistan    
Controlling percentage ownership 100.00% 100.00%  
Closing month December    
GENIE Music Corporation(KT 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 ₩ 139,686 ₩ 110,080 ₩ 90,518
Total liabilities 48,512 41,953 30,704
Operating revenues 156,163 111,450 90,005
Profit (loss) for the year ₩ (3,401) ₩ 8,235 ₩ 3,446
NgeneBio [Member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary   NgeneBio NgeneBio
Total assets   ₩ 6,361 ₩ 7,894
Total liabilities   4,733 4,683
Operating revenues   244  
Profit (loss) for the year   ₩ (1,833) ₩ (434)
KT Innoedu Co., Ltd. [Member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary   KT Innoedu Co., Ltd.  
Total assets   ₩ 6,477  
Total liabilities   7,259  
Operating revenues   15,599  
Profit (loss) for the year   ₩ 103  
KT music contents fund number two [member]      
Disclosure of subsidiaries [Line Items]      
Subsidiary KT Music Contents Fund No.2    
Total assets ₩ 7,500    
Total liabilities 11    
Profit (loss) for the year ₩ (11)