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Decommissioning and Other Provisions - Decommissioning and Restoration (Details) $ in Millions, $ in Millions | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | ---
Dec. 31, 2021 CAD ($) | Dec. 31, 2020 CAD ($) | Dec. 31, 2019 CAD ($) | Dec. 31, 2021 USD ($) | Sep. 30, 2021 CAD ($) | Dec. 31, 2020 USD ($) | Sep. 30, 2020 CAD ($)
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |
Undiscounted cash flows required for future removal of facilities | $ 1,600 |  |  |  |  |  |
Provision for decommissioning, restoration and rehabilitation costs |  |  |  |  | $ 120 |  |
Onerous contracts provision |  | $ 29 |  |  |  |  |
Onerous contract provisions | (14) | (29) | $ 0 |  |  |  |
Gas And Energy Transition |  |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |
Provision for decommissioning, restoration and rehabilitation costs | 47 |  |  |  |  |  |
Centralia Coal Mine |  |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |
Onerous contract provisions | (14) |  |  |  |  |  |
Centralia Coal Mine | Surety Bonds |  |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |
Bonds issued |  |  |  | $ 147 |  | $ 147 |
Alberta Mine | Decommissioning and restoration |  |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |
Provision for decommissioning, restoration and rehabilitation costs |  |  |  |  |  |  | $ 75
Alberta Mine | Letters Of Credit |  |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |
Bonds issued | $ 188 | 131 |  |  |  |  |
Sarnia | Decommissioning and restoration |  |  |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |  |  |
Provision for decommissioning, restoration and rehabilitation costs |  | $ 15 |  |  |  |  |

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