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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