Income Taxes - Significant Components of Deferred Income Tax Assets (Liabilities) (Details) - CAD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Unrecognized deferred income tax assets	$ (52)	$ (21)
Net deferred tax liabilities	(418)	(365)
Cost \| Non-capital losses
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Net deferred income tax liabilities, before unrecognized deferred income tax assets	149	88
Cost \| Future decommissioning and restoration costs
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Net deferred income tax liabilities, before unrecognized deferred income tax assets	184	140
Cost \| Property, plant and equipment
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Net deferred income tax liabilities, before unrecognized deferred income tax assets	(646)	(528)
Cost \| Investment in subsidiaries
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Net deferred income tax liabilities, before unrecognized deferred income tax assets	(60)	(63)
Cost \| Risk management assets and liabilities, net
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Net deferred income tax liabilities, before unrecognized deferred income tax assets	40	99
Cost \| Employee future benefits and compensation plans
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Net deferred income tax liabilities, before unrecognized deferred income tax assets	52	50
Cost \| Foreign exchange differences
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Net deferred income tax liabilities, before unrecognized deferred income tax assets	16	12
Cost \| Other taxable temporary differences
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Net deferred income tax liabilities, before unrecognized deferred income tax assets	(1)	(6)
Accumulated impairment
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Net deferred income tax liabilities, before unrecognized deferred income tax assets	(266)	(208)
Unrecognized deferred income tax assets	$ (152)	$ (157)

The amounts of income taxes recoverable in future periods in respect of: (a) deductible temporary differences; (b) the carryforward of unused tax losses; and (c) the carryforward of unused tax credits. [Refer: Temporary differences [member]; Unused tax credits [member]; Unused tax losses [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 12
-IssueDate 2024-01-01
-Paragraph 81
-Subparagraph g
-Clause i
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=12&code=ifrs-tx-2024-en-r&anchor=para_81_g_i&doctype=Standard
-URIDate 2024-03-27

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2024-01-01
-Paragraph 54
-Subparagraph o
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2024-en-r&anchor=para_54_o&doctype=Standard
-URIDate 2024-03-27

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2024-01-01
-Paragraph 56
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2024-en-r&anchor=para_56&doctype=Standard
-URIDate 2024-03-27

+ Details

Name:	ifrs-full_DeferredTaxAssets
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of deferred tax liabilities or assets. [Refer: Deferred tax liabilities; Deferred tax assets]

+ References

+ Details

Name:	ifrs-full_DeferredTaxLiabilityAsset
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsLineItems
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of deferred tax liabilities net of deferred tax assets, when the absolute amount of deferred tax liabilities is greater than the absolute amount of deferred tax assets. [Refer: Deferred tax assets; Deferred tax liabilities]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 12
-IssueDate 2024-01-01
-Paragraph 81
-Subparagraph g
-Clause i
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=12&code=ifrs-tx-2024-en-r&anchor=para_81_g_i&doctype=Standard
-URIDate 2024-03-27

+ Details

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

- Details

Name:	ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis=ifrs-full_GrossCarryingAmountMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsAxis=ifrs-full_UnusedTaxLossesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsAxis=tac_DecommissioningRestorationAndRehabilitationCostsRelatedTemporaryDifferencesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsAxis=tac_PropertyPlantAndEquipmentRelatedTemporaryDifferencesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsAxis=tac_InvestmentInSubsidiariesRelatedTemporaryDifferencesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsAxis=tac_NetRiskManagementAssetsAndLiabilitiesTemporaryDifferencesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsAxis=tac_EmployeeBenefitsAndCompensationPlansTemporaryDifferencesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsAxis=tac_ForeignExchangeTemporaryDifferencesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsAxis=ifrs-full_OtherTemporaryDifferencesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_CarryingAmountAccumulatedDepreciationAmortisationAndImpairmentAndGrossCarryingAmountAxis=ifrs-full_AccumulatedImpairmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: