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

The amount of outstanding commitments made by the entity in related party transactions. [Refer: Related parties [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 24
-IssueDate 2022-03-24
-Paragraph 18
-Subparagraph b
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=24&code=ifrs-tx-2022-en-r&anchor=para_18_b&doctype=Standard
-URIDate 2022-03-24

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

The cash inflow from the issuing of bonds, notes and debentures.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 7
-IssueDate 2022-03-24
-Paragraph 17
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=7&code=ifrs-tx-2022-en-r&anchor=para_17&doctype=Standard
-URIDate 2022-03-24

Name:	ifrs-full_ProceedsFromIssueOfBondsNotesAndDebentures
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Amount of additional minimum payments required to be under commitments in related party transactions.

No definition available.

Name:	nmg_AdditionalMinimumRequitedPaymentsToBeMadeUnderCommitmentsRelatedPartyTransactions
Namespace Prefix:	nmg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount subscribed each.

No definition available.

Name:	nmg_AmountSubscribedEach
Namespace Prefix:	nmg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Represents the percentage of interest on issued and outstanding common shares.

No definition available.