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Common Shares - Issued and Outstanding (Details) - CAD ($) shares in Millions, $ in Millions |  | 12 Months Ended
--- | --- | ---
Oct. 05, 2023 | Dec. 31, 2024 | Dec. 31, 2023
Common shares |  |  |
Reversal of provision for repurchase of common shares under ASPP |  | $ (19) | $ 19
Provision for repurchase of common shares under ASPP |  |  | (19)
Share buyback tax |  | 2 | $ 0
TransAlta Renewables Inc. |  |  |
Common shares |  |  |
Transaction costs | $ 11 |  |
TransAlta Renewables Inc. | Issued capital |  |  |
Common shares |  |  |
Transaction costs | $ 4 | $ 4 |
Common shares |  |  |
Common shares |  |  |
Issued and outstanding, beginning of period (in shares) |  | 306.9 | 268.1
Reversal (provision) for repurchase of common shares under ASPP (in shares) |  | 1.7 | 0.0
Purchased and cancelled under the NCIB (in shares) |  | (13.5) | (7.5)
Share-based payment plans (in shares) |  | 0.8 | 0.8
Stock options exercised (in shares) |  | 1.6 | 0.7
Issued for acquisition of TransAlta Renewables (in shares) |  | 0.0 | 46.5
Provision for repurchase of common shares under ASPP (in shares) |  | 0.0 | (1.7)
Issued and outstanding, end of year, prior to ASPP (in shares) |  | 297.5 | 306.9
Issued and outstanding, end of year |  | $ 3,285 | $ 2,863
Reversal of provision for repurchase of common shares under ASPP |  | 19 | 0
Purchased and cancelled under the NCIB |  | (146) | (80)
Share-based payment plans |  | 9 | 6
Stock options exercised |  | 12 | 5
Issued for acquisition of TransAlta Renewables |  | 0 | 510
Provision for repurchase of common shares under ASPP |  | 0 | (19)
Issued and outstanding, end of year |  | $ 3,179 | $ 3,285
Common shares | Prior To Automatic Share Purchase Plan |  |  |
Common shares |  |  |
Issued and outstanding, beginning of period (in shares) |  | 308.6 |
Issued and outstanding, end of year, prior to ASPP (in shares) |  | 297.5 | 308.6
Issued and outstanding, end of year |  | $ 3,304 |
Issued and outstanding, end of year |  | $ 3,179 | $ 3,304

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- Definition The amount of acquisition-related costs for transactions recognised separately from the acquisition of assets and the assumption of liabilities in business combinations. [Refer: Total for all business combinations [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 3 -IssueDate 2024-01-01 -Paragraph B64 -Subparagraph m -URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=3&code=ifrs-tx-2024-en-r&anchor=para_B64_m&doctype=Appendix&subtype=B -URIDate 2024-03-27 + Details
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- Definition Adjustments for share-based payments to reconcile profit (loss) to net cash flow from (used in) operating activities. [Refer: Profit (loss)] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 7 -IssueDate 2024-01-01 -Paragraph 20 -Subparagraph b -URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=7&code=ifrs-tx-2024-en-r&anchor=para_20_b&doctype=Standard -URIDate 2024-03-27 + Details
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