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Decommissioning and Other Provisions - Decommissioning and Restoration - Narrative (Details) $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2023 CAD ($) | Dec. 31, 2022 CAD ($) | Dec. 31, 2021 CAD ($) | Dec. 31, 2023 USD ($) | Dec. 31, 2022 USD ($)
Disclosure of detailed information about borrowings [line items] |  |  |  |  |
Undiscounted cash amount | $ 1,700,000,000 |  |  |  |
Increase (decrease) in PP&E | 31,000,000 | $ (123,000,000) |  |  |
Reversal of impairment loss | (21,000,000) | (102,000,000) |  |  |
Revisions in discount rates | 52,000,000 | (225,000,000) |  |  |
Increase (decrease) through change in estimated cash flows | (89,000,000) | 100,000,000 |  |  |
Onerous contract provisions | 0 | 0 | $ (14,000,000) |  |
Gas |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |
Decommissioning and restoration provision | 34,000,000 | 46,000,000 |  |  |
Centralia Coal Mine | Surety Bonds |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |
Bonds issued |  |  |  | $ 147 | $ 147
Alberta Mine | Letters Of Credit |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |
Bonds issued | 188,000,000 | 187,000,000 |  |  |
Minimum |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |
Revisions in discount rates | 6.0 | 7.0 |  |  |
Maximum |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |
Revisions in discount rates | 0.090 | 9.7 |  |  |
Decommissioning and restoration |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |
Decommissioning and restoration provision | 52,000,000 | 225,000,000 |  |  |
Decommissioning and restoration |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |
Increase (decrease) in PP&E | 55,000,000 | 49,000,000 |  |  |
Revisions in discount rates | 52,000,000 | (225,000,000) |  |  |
Increase (decrease) through change in estimated cash flows | $ (89,000,000) | $ 95,000,000 |  |  |

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