Intangible Assets (Details) - CAD ($) $ in Millions	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023
Reconciliation of changes in intangible assets other than goodwill [abstract]
Beginning balance	$ 223	$ 252
Change in foreign exchange rates	6	(2)
Ending balance	281	223
Cost
Reconciliation of changes in intangible assets other than goodwill [abstract]
Beginning balance	875	868
Additions	10	13
Acquisitions (Note 4)	57
Change in foreign exchange rates	13	(5)
Asset impairment charges		(1)
Transfers	22	0
Ending balance	977	875
Accumulated amortization
Reconciliation of changes in intangible assets other than goodwill [abstract]
Beginning balance	(652)	(616)
Change in foreign exchange rates	7	(2)
Transfers	(1)
Amortization	38	38
Ending balance	(696)	(652)
Power sale and other contracts
Reconciliation of changes in intangible assets other than goodwill [abstract]
Beginning balance	96	114
Ending balance	155	96
Power sale and other contracts \| Cost
Reconciliation of changes in intangible assets other than goodwill [abstract]
Beginning balance	270	272
Additions	0	0
Acquisitions (Note 4)	57
Change in foreign exchange rates	5	(2)
Asset impairment charges		0
Transfers	20	0
Ending balance	352	270
Power sale and other contracts \| Accumulated amortization
Reconciliation of changes in intangible assets other than goodwill [abstract]
Beginning balance	(174)	(158)
Change in foreign exchange rates	4	(1)
Transfers	0
Amortization	19	17
Ending balance	(197)	(174)
Software
Reconciliation of changes in intangible assets other than goodwill [abstract]
Beginning balance	100	111
Ending balance	121	100
Software \| Cost
Reconciliation of changes in intangible assets other than goodwill [abstract]
Beginning balance	446	437
Additions	0	0
Acquisitions (Note 4)	0
Change in foreign exchange rates	7	(2)
Asset impairment charges		(1)
Transfers	35	12
Ending balance	488	446
Software \| Accumulated amortization
Reconciliation of changes in intangible assets other than goodwill [abstract]
Beginning balance	(346)	(326)
Change in foreign exchange rates	3	(1)
Transfers	(1)
Amortization	19	21
Ending balance	(367)	(346)
Intangibles under development
Reconciliation of changes in intangible assets other than goodwill [abstract]
Beginning balance	27	27
Ending balance	5	27
Intangibles under development \| Cost
Reconciliation of changes in intangible assets other than goodwill [abstract]
Beginning balance	27	27
Additions	10	13
Acquisitions (Note 4)	0
Change in foreign exchange rates	1	(1)
Asset impairment charges		0
Transfers	(33)	(12)
Ending balance	5	27
Intangibles under development \| Accumulated amortization
Reconciliation of changes in intangible assets other than goodwill [abstract]
Beginning balance	0	0
Change in foreign exchange rates	0	0
Transfers	0
Amortization	0	0
Ending balance	0	0
Coal rights
Reconciliation of changes in intangible assets other than goodwill [abstract]
Beginning balance	0	0
Ending balance	0	0
Coal rights \| Cost
Reconciliation of changes in intangible assets other than goodwill [abstract]
Beginning balance	132	132
Additions	0	0
Acquisitions (Note 4)	0
Change in foreign exchange rates	0	0
Asset impairment charges		0
Transfers	0	0
Ending balance	132	132
Coal rights \| Accumulated amortization
Reconciliation of changes in intangible assets other than goodwill [abstract]
Beginning balance	(132)	(132)
Change in foreign exchange rates	0	0
Transfers	0
Amortization	0	0
Ending balance	$ (132)	$ (132)

The increase in intangible assets other than goodwill resulting from acquisitions through business combinations. [Refer: Total for all business combinations [member]; Intangible assets other than goodwill]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 38
-IssueDate 2024-01-01
-Paragraph 118
-Subparagraph e
-Clause i
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=38&code=ifrs-tx-2024-en-r&anchor=para_118_e_i&doctype=Standard
-URIDate 2024-03-27

+ Details

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

- Definition

The amount of additions to intangible assets other than goodwill, other than those acquired through business combinations. [Refer: Total for all business combinations [member]; Intangible assets other than goodwill]

+ References

+ Details

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

- Definition

The amount of amortisation of intangible assets other than goodwill. [Refer: Depreciation and amortisation expense; Intangible assets other than goodwill]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 38
-IssueDate 2024-01-01
-Paragraph 118
-Subparagraph e
-Clause vi
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=38&code=ifrs-tx-2024-en-r&anchor=para_118_e_vi&doctype=Standard
-URIDate 2024-03-27

+ Details

Name:	ifrs-full_AmortisationIntangibleAssetsOtherThanGoodwill
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of impairment loss recognised in profit or loss for intangible assets other than goodwill. [Refer: Impairment loss recognised in profit or loss; Intangible assets other than goodwill]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 38
-IssueDate 2024-01-01
-Paragraph 118
-Subparagraph e
-Clause iv
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=38&code=ifrs-tx-2024-en-r&anchor=para_118_e_iv&doctype=Standard
-URIDate 2024-03-27

+ Details

Name:	ifrs-full_ImpairmentLossRecognisedInProfitOrLossIntangibleAssetsOtherThanGoodwill
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

The increase (decrease) in intangible assets other than goodwill resulting from net exchange differences arising on the translation of the financial statements from the functional currency into a different presentation currency, including the translation of a foreign operation into the presentation currency of the reporting entity. [Refer: Intangible assets other than goodwill]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 38
-IssueDate 2024-01-01
-Paragraph 118
-Subparagraph e
-Clause vii
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=38&code=ifrs-tx-2024-en-r&anchor=para_118_e_vii&doctype=Standard
-URIDate 2024-03-27

+ Details

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

- Definition

The increase (decrease) in intangible assets other than goodwill resulting from transfers. [Refer: Intangible assets other than goodwill]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 38
-IssueDate 2024-01-01
-Paragraph 118
-Subparagraph e
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=38&code=ifrs-tx-2024-en-r&anchor=para_118_e&doctype=Standard
-URIDate 2024-03-27

+ Details

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

- Definition

The amount of identifiable non-monetary assets without physical substance. This amount does not include goodwill. [Refer: Goodwill]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 38
-IssueDate 2024-01-01
-Paragraph 118
-Subparagraph e
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=38&code=ifrs-tx-2024-en-r&anchor=para_118_e&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 c
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2024-en-r&anchor=para_54_c&doctype=Standard
-URIDate 2024-03-27

+ Details

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

- References

No definition available.

+ Details

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

- Details

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

- Details

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

- Details

Name:	ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillAxis=ifrs-full_OtherIntangibleAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillAxis=ifrs-full_ComputerSoftwareMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillAxis=ifrs-full_IntangibleAssetsUnderDevelopmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_ClassesOfIntangibleAssetsOtherThanGoodwillAxis=ifrs-full_MiningRightsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: