Warrants - Fair value of warrant liabilities (Details) - Private Warrants $ in Thousands	6 Months Ended
Jun. 30, 2025 USD ($)
Warrants
Warrants liability as at December 31, 2024	$ 912
Increase in fair value of warrants liability	16,670
Warrants liability as at June 30, 2025	$ 17,582

Amount of increase (decrease) of financial instrument classified as a liabilities measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

No definition available.

Name:	tmc_FairValueMeasurementWithUnobservableInputsReconciliationRecurringAndNonrecurringBasisLiabilityGainLoss
Namespace Prefix:	tmc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration