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Credit Facilities, Long-Term Debt and Lease Liabilities - Restrictions on Non-Recourse Debt and Security (Details) $ in Millions, $ in Millions |  | 12 Months Ended
--- | --- | ---
Jul. 20, 2018 CAD ($) | Dec. 31, 2021 CAD ($) | Dec. 31, 2021 AUD ($) | Dec. 31, 2020 CAD ($) | Dec. 31, 2019 CAD ($)
Disclosure of detailed information about borrowings [line items] |  |  |  |  |
Other borrowings |  | $ 735 |  | $ 730 |
Borrowings |  | 3,267 |  | 3,361 |
PP&E |  | 5,320 |  | 5,822 | $ 6,207
Intangible assets |  | 256 |  | 313 | 318
Alberta Off-Coal Agreement | $ 40 | 40 |  | 40 | $ 40
Alberta off-coal agreement, annual cash payments, net |  | 37 |  |  |
TransAlta OCP |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |
Restricted cash (Note 22) |  | 17 |  | 17 |
Renewable generation facilities |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |
PP&E |  | 1,500 |  | 1,000 |
Intangible assets |  | 78 |  | 88 |
Non-recourse debt |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |
Other borrowings |  | 1,900 |  | 1,800 |
Restricted cash (Note 22) |  | 67 |  | 73 |
Borrowings |  | 221 |  |  |
Borrowings, make-whole amount |  | 39 |  |  |
Adjustments for undistributed profits of associates |  | 6 |  |  |
Non-recourse debt | Secured by first rate ranking charge over subsidiaries |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |
Notional amount |  | 1,500 |  | 1,400 |
Non-recourse debt | Secured by equity interests of the issuer |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |
Notional amount |  | 103 |  | 111 |
Restricted Use Debt |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |
Proceeds from issue of bonds, notes and debentures |  | 3 | $ 4 |  |
Secured Debt | TransAlta OCP |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |
Notional amount |  | $ 263 |  | $ 285 |

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