Share-Based Compensation - Schedule of company's stock options granted and outstanding under the STIP (Details). - shares	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023
Class of Warrant or Right
Options Exercisable	14,300,575
December 31, 2025
Class of Warrant or Right
Expiry Date	Dec. 31, 2025
Exercise price	0.65
Weighted average life to expiry (years)	1 year
Options Exercisable	11,578
January 27, 2026
Class of Warrant or Right
Expiry Date	Jan. 27, 2026
Weighted average life to expiry (years)	1 year 25 days
Options Exercisable	590,509
January 27, 2026 \| Minimum
Class of Warrant or Right
Exercise price	0.52
January 27, 2026 \| Maximum
Class of Warrant or Right
Exercise price	$2.59
February 2, 2026
Class of Warrant or Right
Expiry Date	Feb. 02, 2026
Exercise price	0.65
Weighted average life to expiry (years)	1 year 1 month 2 days
Options Exercisable	57,893
February 17, 2026
Class of Warrant or Right
Expiry Date	Feb. 17, 2026
Weighted average life to expiry (years)	1 year 1 month 17 days
Options Exercisable	431,493
February 17, 2026 \| Minimum
Class of Warrant or Right
Exercise price	0.22
February 17, 2026 \| Maximum
Class of Warrant or Right
Exercise price	$0.52
June 1, 2028
Class of Warrant or Right
Expiry Date	Jun. 01, 2028
Weighted average life to expiry (years)	3 years 5 months 1 day
Options Exercisable	12,514,385
June 1, 2028 \| Minimum
Class of Warrant or Right
Exercise price	0.65	2.59
June 1, 2028 \| Maximum
Class of Warrant or Right
Exercise price	$8.64
June 30, 2028
Class of Warrant or Right
Expiry Date	Jun. 30, 2028
Exercise price	2.59
Weighted average life to expiry (years)	3 years 6 months
Options Exercisable	694,717

No definition available.

Name:	tmc_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionOutstandingWeightedAveragesExercisePrice
Namespace Prefix:	tmc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

Name:	us-gaap_ClassOfWarrantOrRightLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Date when the debt instrument is scheduled to be fully repaid, in YYYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22)(a)(2))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

Reference 4: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B

+ Details

Name:	us-gaap_DebtInstrumentMaturityDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iii)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Weighted average remaining contractual term of outstanding stock options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 718
-SubTopic 10
-Subparagraph (e)(1)
-Name Accounting Standards Codification
-Paragraph 2
-Section 50
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_AwardDateAxis=tmc_December312025Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardDateAxis=tmc_January272026Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardDateAxis=tmc_February22026Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardDateAxis=tmc_February172026Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardDateAxis=tmc_June12028Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardDateAxis=tmc_June302028Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: