Related Party Transactions - Summary of Related Parties Outstanding Balances of Receivables and Payables (Detail) - KRW (₩) ₩ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of transactions between related parties [line items]
Payables	₩ 57,907
Trade receivables [member]
Disclosure of transactions between related parties [line items]
Receivables	1,625	₩ 2,078
Trade receivables [member] \| K-Realty CR-REITs No.1 [member]
Disclosure of transactions between related parties [line items]
Receivables	608	674
Trade receivables [member] \| K Bank Inc. [member]
Disclosure of transactions between related parties [line items]
Receivables	583	627
Trade receivables [member] \| Others [member]
Disclosure of transactions between related parties [line items]
Receivables	434	777
Loans and receivables [member]
Disclosure of transactions between related parties [line items]
Receivables	37,941	44,570
Loans and receivables [member] \| K-Realty CR-REITs No.1 [member]
Disclosure of transactions between related parties [line items]
Receivables	23,100	30,910
Loans and receivables [member] \| K Bank Inc. [member]
Disclosure of transactions between related parties [line items]
Receivables	13,664	12,435
Loans and receivables [member] \| Others [member]
Disclosure of transactions between related parties [line items]
Receivables	1,177	1,225
Trade payables [member]
Disclosure of transactions between related parties [line items]
Payables		4
Trade payables [member] \| Others [member]
Disclosure of transactions between related parties [line items]
Payables		4
Other payables [member]
Disclosure of transactions between related parties [line items]
Payables	1,268	1,412
Other payables [member] \| K-Realty CR-REITs No.1 [member]
Disclosure of transactions between related parties [line items]
Payables	57,907
Other payables [member] \| K Bank Inc. [member]
Disclosure of transactions between related parties [line items]
Payables	557	296
Other payables [member] \| Others [member]
Disclosure of transactions between related parties [line items]
Payables	₩ 711	₩ 1,116

The amounts payable resulting from related party transactions. [Refer: Related parties [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 24
-IssueDate 2019-01-01
-Paragraph 20
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=24&code=ifrs-tx-2019-en-r&anchor=para_20&doctype=Standard
-URIDate 2019-03-27

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 24
-IssueDate 2019-01-01
-Paragraph 18
-Subparagraph b
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=24&code=ifrs-tx-2019-en-r&anchor=para_18_b&doctype=Standard
-URIDate 2019-03-27

+ Details

Name:	ifrs-full_AmountsPayableRelatedPartyTransactions
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amounts receivable resulting from related party transactions. [Refer: Related parties [member]]

+ References

+ Details

Name:	ifrs-full_AmountsReceivableRelatedPartyTransactions
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

+ References

No definition available.

+ Details

Name:	ifrs-full_DisclosureOfTransactionsBetweenRelatedPartiesLineItems
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	ifrs-full_ClassesOfFinancialInstrumentsAxis=ifrs-full_TradeReceivablesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_CategoriesOfRelatedPartiesAxis=kt_KrealtyCrReitsNoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_CategoriesOfRelatedPartiesAxis=kt_KBankIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_CategoriesOfRelatedPartiesAxis=ifrs-full_OtherRelatedPartiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_ClassesOfFinancialInstrumentsAxis=ifrs-full_LoansAndReceivablesCategoryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_ClassesOfFinancialInstrumentsAxis=kt_TradePayablesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_ClassesOfFinancialInstrumentsAxis=kt_OtherPayablesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: