Name:	gmab_OperatingAssetsAndLiabilitiesAbstract
Namespace Prefix:	gmab_
Data Type:	xbrli:stringItemType
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Period Type:	duration

The amount of receivables for securities matured.

No definition available.

Name:	gmab_ReceivablesForSecuritiesMatured
Namespace Prefix:	gmab_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The amount by which credit derivatives or similar instruments related to loans or receivables mitigate maximum exposure to credit risk. [Refer: Loans and receivables; Credit risk [member]; Maximum exposure to credit risk; Derivatives [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Expiry date 2023-01-01
-Name IFRS
-Number 7
-IssueDate 2022-03-24
-Paragraph 9
-Subparagraph b
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2017-en-b&anchor=para_9_b&doctype=Standard&book=b
-URIDate 2022-03-24

Name:	ifrs-full_AmountByWhichLoansOrReceivablesRelatedCreditDerivativesOrSimilarInstrumentsMitigateMaximumExposureToCreditRisk
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

The amount of interest recognised as a receivable.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2022-03-24
-Paragraph 112
-Subparagraph c
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2022-en-r&anchor=para_112_c&doctype=Standard
-URIDate 2022-03-24

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

The amount of non-current trade receivables and non-current other receivables. [Refer: Non-current trade receivables; Other non-current receivables]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2022-03-24
-Paragraph 54
-Subparagraph h
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2022-en-r&anchor=para_54_h&doctype=Standard
-URIDate 2022-03-24

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2022-03-24
-Paragraph 78
-Subparagraph b
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2022-en-r&anchor=para_78_b&doctype=Standard
-URIDate 2022-03-24

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

The amount receivable by the entity that it does not separately disclose in the same statement or note.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Name IAS
-Number 1
-IssueDate 2022-03-24
-Paragraph 78
-Subparagraph b
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2022-en-r&anchor=para_78_b&doctype=Standard
-URIDate 2022-03-24

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

Receivables that represent amounts paid for goods and services before they have been delivered.

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

The amount of current trade receivables and current other receivables. [Refer: Current trade receivables; Other current receivables]

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

The amount due from customers for goods and services sold.