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Asset Impairment (Details) $ in Millions, $ in Millions | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Sep. 30, 2021 CAD ($) | Dec. 31, 2021 CAD ($) MW | Dec. 31, 2020 CAD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 CAD ($) | Oct. 01, 2019 MW
Disclosure of impairment loss recognised or reversed [line items] |  |  |  |  |  |
Asset impairment charge |  | $ 648 | $ 84 |  | $ 25 |
Estimated salvage value |  | 33 |  |  |  |
Impairment charges |  | 345 | 79 |  |  |
Provision for decommissioning, restoration and rehabilitation costs | $ 120 |  |  |  |  |
Assets |  | 9,226 | 9,747 |  |  |
Gross carrying amount |  |  |  |  |  |
Disclosure of impairment loss recognised or reversed [line items] |  |  |  |  |  |
Write-downs (reversals of write-downs) of property, plant and equipment |  | $ 589 | $ 81 |  |  |
Discount rate, measurement input |  |  |  |  |  |
Disclosure of impairment loss recognised or reversed [line items] |  |  |  |  |  |
Significant unobservable input, assets |  | 5,000,000.0 | 5,300,000 |  |  |
Assets Held for Sale |  |  |  |  |  |
Disclosure of impairment loss recognised or reversed [line items] |  |  |  |  |  |
Estimated salvage value |  | $ 25 |  |  |  |
Impairment charges |  | 0 | $ 0 |  | 15 |
Energy Transition |  |  |  |  |  |
Disclosure of impairment loss recognised or reversed [line items] |  |  |  |  |  |
Asset impairment charge |  | 191 |  |  |  |
Keephills Unit 1 | Energy Transition |  |  |  |  |  |
Disclosure of impairment loss recognised or reversed [line items] |  |  |  |  |  |
Asset impairment charge |  | 94 |  |  |  |
Sundance Unit 4 | Energy Transition |  |  |  |  |  |
Disclosure of impairment loss recognised or reversed [line items] |  |  |  |  |  |
Asset impairment charge |  | 56 |  |  |  |
Centralia Thermal Facility |  |  |  |  |  |
Disclosure of impairment loss recognised or reversed [line items] |  |  |  |  |  |
Provision for decommissioning, restoration and rehabilitation costs |  |  |  |  | 141 |
Reversal of impairment loss |  |  |  |  | 151 |
Wind Facilities |  |  |  |  |  |
Disclosure of impairment loss recognised or reversed [line items] |  |  |  |  |  |
Impairment charges | $ 10 |  |  |  |  |
Wind Facilities | Level III | Investment property [member] | Non-recurring fair value measurement [member] |  |  |  |  |  |
Disclosure of impairment loss recognised or reversed [line items] |  |  |  |  |  |
Assets |  | 65 |  |  |  |
Kent Hills Wind L.P. |  |  |  |  |  |
Disclosure of impairment loss recognised or reversed [line items] |  |  |  |  |  |
Impairment charges |  | $ 2 |  |  |  |
Capacity of facility (in megawatts) | MW |  | 167 |  |  |  |
Property, plant and equipment | Sundance Unit 3 |  |  |  |  |  |
Disclosure of impairment loss recognised or reversed [line items] |  |  |  |  |  |
Impairment loss |  |  | 70 |  |  |
Land |  |  |  |  |  |
Disclosure of impairment loss recognised or reversed [line items] |  |  |  |  |  |
Impairment loss |  |  | 9 | $ 7 |  |
Land | Gross carrying amount |  |  |  |  |  |
Disclosure of impairment loss recognised or reversed [line items] |  |  |  |  |  |
Write-downs (reversals of write-downs) of property, plant and equipment |  | $ 0 | 9 |  |  |
Kaybob Cogeneration Project |  |  |  |  |  |
Disclosure of impairment loss recognised or reversed [line items] |  |  |  |  |  |
Capacity of facility (in megawatts) | MW |  |  |  |  |  | 40
Mining assets | Highvale Mine |  |  |  |  |  |
Disclosure of impairment loss recognised or reversed [line items] |  |  |  |  |  |
Impairment charges |  | $ 195 | $ 0 |  | $ 0 |

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