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Asset Impairment - Detailed information about property, plant, and equipment (Details) - CAD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Disclosure of detailed information about property, plant and equipment [line items]      
Impairment charges $ 345 $ 79  
Impairment reversal     $ (151)
Asset impairment charge 648 84 25
Assets Held for Sale      
Disclosure of detailed information about property, plant and equipment [line items]      
Impairment charges 0 0 15
Decommissioning and restoration      
Disclosure of detailed information about property, plant and equipment [line items]      
Impairment charges 32 0 2
Wind      
Disclosure of detailed information about property, plant and equipment [line items]      
Impairment charges 12 0 0
Hydro      
Disclosure of detailed information about property, plant and equipment [line items]      
Impairment charges 5 2 0
Gas      
Disclosure of detailed information about property, plant and equipment [line items]      
Impairment charges 5 0 0
Coal Rights      
Disclosure of detailed information about property, plant and equipment [line items]      
Impairment charges 17 0 0
Project Development Costs      
Disclosure of detailed information about property, plant and equipment [line items]      
Impairment charges 10 0 18
Write-downs (reversals of write-downs) of property, plant and equipment 1 0 18
Project Development Costs | Hydro generation      
Disclosure of detailed information about property, plant and equipment [line items]      
Write-downs (reversals of write-downs) of property, plant and equipment 9    
Centralia Mine | Decommissioning and restoration      
Disclosure of detailed information about property, plant and equipment [line items]      
Impairment charges 0 3 141
Highvale Mine | Mining assets      
Disclosure of detailed information about property, plant and equipment [line items]      
Impairment charges 195 0 0
Kaybob Cogeneration Project      
Disclosure of detailed information about property, plant and equipment [line items]      
Impairment charges $ 27 $ 0 $ 0