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Credit Facilities, Long-Term Debt and Lease Liabilities - Restricted Cash and Letters of Credit (Details) - CAD ($) $ in Millions | Dec. 31, 2024 | Jun. 30, 2024 | Dec. 31, 2023
--- | --- | --- | ---
Letter of credit |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |
Outstanding letters of credit | $ 865 |  | $ 782
Exercised amount | 0 |  | 0
Committed |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |
Facility size | 2,916 |  |
Outstanding letters of credit | 645 |  |
Committed | Syndicated credit facility |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |
Facility size | 1,950 |  |
Outstanding letters of credit | 456 |  |
Committed | Bilateral credit facilities |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |
Facility size | 240 |  |
Outstanding letters of credit | 161 |  |
Non-committed |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |
Facility size | 400 |  |
Outstanding letters of credit | 220 |  |
TransAlta OCP |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |
Restricted cash | 17 |  | 17
TEC |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |
Restricted cash | 52 |  | $ 52
TransAlta Renewables Inc. | Non-committed | Demand facilities |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |
Facility size |  | $ 400 |
Outstanding letters of credit | $ 220 |  |

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