Name:	gtmay_NetTaxProfitAccountAbstract
Namespace Prefix:	gtmay_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The tax rate applied to dividend distributions from the Net After Tax Profit Account (CUFIN) when the dividends are distributed in an amount higher than the balance of the Net After Tax Profit Account.

No definition available.

Name:	gtmay_NetTaxProfitAccountDividendDistributionIncomeTaxRate
Namespace Prefix:	gtmay_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Refers to the period over which the entity may apply a tax credit to income taxes due from dividend distributions not drawn from the Net After Tax Profit Account.

No definition available.

Name:	gtmay_NetTaxProfitAccountDividendDistributionTaxCreditPeriod
Namespace Prefix:	gtmay_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

The amount received or receivable from the issuance of the entity's shares and amounts received from other transactions involving the entity's stock or stockholders.

No definition available.

Name:	gtmay_PaidInCapital
Namespace Prefix:	gtmay_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

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

- References

No definition available.

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

The number of shares that have been authorised and issued, reduced by treasury shares held. [Refer: Treasury shares]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2018-01-01
-Paragraph 79
-Subparagraph a
-Clause iv
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_79_a_iv&doctype=Standard
-URIDate 2018-03-16