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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 24
-IssueDate 2021-01-01
-Paragraph 20
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=24&code=ifrs-tx-2021-en-r&anchor=para_20&doctype=Standard
-URIDate 2021-03-24

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 24
-IssueDate 2021-01-01
-Paragraph 18
-Subparagraph b
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=24&code=ifrs-tx-2021-en-r&anchor=para_18_b&doctype=Standard
-URIDate 2021-03-24

+ 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 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

- Definition

The percentage of voting equity interests acquired in a business combination. [Refer: Business combinations [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 3
-IssueDate 2021-01-01
-Paragraph B64
-Subparagraph c
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=3&code=ifrs-tx-2021-en-r&anchor=para_B64_c&doctype=Appendix&subtype=B
-URIDate 2021-03-24

+ Details

Name:	ifrs-full_PercentageOfVotingEquityInterestsAcquired
Namespace Prefix:	ifrs-full_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The cash outflow for the purchases of long-term assets that the entity does not separately disclose in the same statement or note, classified as investing activities. [Refer: Assets]

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Name IAS
-Number 7
-IssueDate 2021-01-01
-Paragraph 16
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=7&code=ifrs-tx-2021-en-r&anchor=para_16_a&doctype=Standard
-URIDate 2021-03-24

+ Details

Name:	ifrs-full_PurchaseOfOtherLongtermAssetsClassifiedAsInvestingActivities
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=gb_TwigMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=gb_ToshiMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

Interests in other entities - Narrative (Details) € in Thousands, £ in Millions					12 Months Ended
	Feb. 14, 2022 EUR (€)	Feb. 14, 2022 GBP (£)	Feb. 01, 2022 EUR (€)	Feb. 01, 2022 GBP (£)	Mar. 31, 2022 EUR (€)	Mar. 31, 2021 EUR (€)	Mar. 31, 2020 EUR (€)
Disclosure of transactions between related parties [line items]
Acquisitions of non-current financial assets					€ 7,637	€ 1,016	€ 7,856
Twig
Disclosure of transactions between related parties [line items]
Percentage of voting equity interests acquired			1.00%	1.00%
Acquisitions of non-current financial assets			€ 1,200	£ 1.0
Toshi
Disclosure of transactions between related parties [line items]
Percentage of voting equity interests acquired	17.45%	17.45%
Acquisitions of non-current financial assets	€ 2,500	£ 2.1
Joint Ventures and Associates
Disclosure of transactions between related parties [line items]
Amounts receivable, related party transactions					€ 0	€ 600	€ 1,500