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Commitments and Contingencies - Summary of Guarantees Provided by the Group for Third Parties (Detail) - KRW (₩)
₩ in Millions
 12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Disclosure of detailed information about borrowings [line items]    
Used amount ₩ 10,006,685 ₩ 8,437,703
KT Engineering Co Ltd [Member] | Shinhan Bank [member] | Guarantees [member]    
Disclosure of detailed information about borrowings [line items]    
Subject to payment guarantees Gasan Solar Power Plant Inc.  
Limit ₩ 4,700  
Used amount ₩ 672  
KT Engineering Co Ltd [Member] | Suhyup Bank [Member] | Guarantees [member]    
Disclosure of detailed information about borrowings [line items]    
Subject to payment guarantees SPP Inc.  
Limit ₩ 3,250  
Used amount ₩ 345  
KT Engineering Co Ltd [Member] | Suhyup Bank One [Member] | Guarantees [member]    
Disclosure of detailed information about borrowings [line items]    
Subject to payment guarantees Korea Cell Inc.  
Limit ₩ 3,250  
Used amount ₩ 338  
KT Engineering Co Ltd [Member] | Suhyup Bank Two [Member] | Guarantees [member]    
Disclosure of detailed information about borrowings [line items]    
Subject to payment guarantees San-Ya Agricultural Association Corporation  
Limit ₩ 3,250  
Used amount ₩ 345  
KT Alpha Co Ltd KT Hitel Co Ltd [Member] | T-commerce cash payers [Member] | Guarantees [member]    
Disclosure of detailed information about borrowings [line items]    
Subject to payment guarantees Cash payers  
Limit ₩ 860  
Used amount ₩ 0  
Nasmedia Co Ltd [member] | Korea Securities Finance Corp [Member] | Guarantees [member]    
Disclosure of detailed information about borrowings [line items]    
Subject to payment guarantees Stockholders Association Members  
Limit ₩ 5,654  
Used amount ₩ 986  
Bottom of range [member] | KT Engineering Co Ltd [Member] | Shinhan Bank [member] | Guarantees [member]    
Disclosure of detailed information about borrowings [line items]    
Maturity Jan. 7, 2010  
Bottom of range [member] | KT Engineering Co Ltd [Member] | Suhyup Bank [Member] | Guarantees [member]    
Disclosure of detailed information about borrowings [line items]    
Maturity Feb. 17, 2014  
Bottom of range [member] | KT Engineering Co Ltd [Member] | Suhyup Bank One [Member] | Guarantees [member]    
Disclosure of detailed information about borrowings [line items]    
Maturity Feb. 17, 2014  
Bottom of range [member] | KT Engineering Co Ltd [Member] | Suhyup Bank Two [Member] | Guarantees [member]    
Disclosure of detailed information about borrowings [line items]    
Maturity Feb. 17, 2014  
Bottom of range [member] | KT Alpha Co Ltd KT Hitel Co Ltd [Member] | T-commerce cash payers [Member] | Guarantees [member]    
Disclosure of detailed information about borrowings [line items]    
Maturity Apr. 14, 2022  
Top of range [member] | KT Engineering Co Ltd [Member] | Shinhan Bank [member] | Guarantees [member]    
Disclosure of detailed information about borrowings [line items]    
Maturity Jan. 8, 2025  
Top of range [member] | KT Engineering Co Ltd [Member] | Suhyup Bank [Member] | Guarantees [member]    
Disclosure of detailed information about borrowings [line items]    
Maturity Feb. 16, 2024  
Top of range [member] | KT Engineering Co Ltd [Member] | Suhyup Bank One [Member] | Guarantees [member]    
Disclosure of detailed information about borrowings [line items]    
Maturity Feb. 16, 2024  
Top of range [member] | KT Engineering Co Ltd [Member] | Suhyup Bank Two [Member] | Guarantees [member]    
Disclosure of detailed information about borrowings [line items]    
Maturity Feb. 16, 2024  
Top of range [member] | KT Alpha Co Ltd KT Hitel Co Ltd [Member] | T-commerce cash payers [Member] | Guarantees [member]    
Disclosure of detailed information about borrowings [line items]    
Maturity Apr. 14, 2023