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Business Acquisitions - Alta Renewables (Details) $ / shares in Units, shares in Millions, $ in Millions |  | 12 Months Ended
--- | --- | ---
Oct. 05, 2023 CAD ($) shares $ / shares | Dec. 31, 2024 CAD ($) | Dec. 31, 2023 CAD ($)
Disclosure of detailed information about business combination [line items] |  |  |
Non-controlling Interests, reduced |  |  | $ 809
Committed |  |  |
Disclosure of detailed information about business combination [line items] |  |  |
Facility size |  | $ 2,916 |
Committed | Syndicated credit facility |  |  |
Disclosure of detailed information about business combination [line items] |  |  |
Facility size |  | 1,950 |
Deficit |  |  |
Disclosure of detailed information about business combination [line items] |  |  |
Non-controlling Interests, reduced |  |  | 625
Attributable to non-controlling interests |  |  |
Disclosure of detailed information about business combination [line items] |  |  |
Non-controlling Interests, reduced | $ 630 |  | 630
Other |  |  |
Disclosure of detailed information about business combination [line items] |  |  |
Change in ownership of TransAlta Renewables | 64 | 0 | $ (64)
TransAlta Renewables Inc. |  |  |
Disclosure of detailed information about business combination [line items] |  |  |
Total purchase consideration transferred | 1,300 |  |
Cash consideration | $ 800 |  |
Common shares issued (in shares) | shares | 46 |  |
Value of common shares issued | $ 514 |  |
Price per share of shares issued (in CAD per share) | $ / shares | $ 11.06 |  |
Transaction costs | $ 11 |  |
TransAlta Renewables Inc. | Committed | Syndicated credit facility |  |  |
Disclosure of detailed information about business combination [line items] |  |  |
Additional borrowings | 700 |  |
Facility size | 2,000 |  |
TransAlta Renewables Inc. | Issued capital |  |  |
Disclosure of detailed information about business combination [line items] |  |  |
Transaction costs | 4 | $ 4 |
TransAlta Renewables Inc. | Deficit |  |  |
Disclosure of detailed information about business combination [line items] |  |  |
Transaction costs | $ 7 |  |

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