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Decommissioning and Other Provisions - Decommissioning and Restoration - Narrative (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2024
CAD ($)
Dec. 31, 2023
CAD ($)
Dec. 31, 2024
USD ($)
Dec. 04, 2024
CAD ($)
Dec. 31, 2023
USD ($)
Disclosure of detailed information about borrowings [line items]          
Undiscounted cash amount $ 1,800,000,000        
Increase in PP&E 18,000,000 $ 31,000,000      
Increase through change in estimated cash flows 41,000,000 (89,000,000)      
Revisions in discount rates 35,000,000 52,000,000      
Reversal of impairment loss 17,000,000 21,000,000      
Heartland Generation          
Disclosure of detailed information about borrowings [line items]          
Decommissioning provisions       $ 101,000,000  
Other provisions       $ 55,000,000  
Heartland Generation | Gas          
Disclosure of detailed information about borrowings [line items]          
Other provisions 47,000,000        
Minimum          
Disclosure of detailed information about borrowings [line items]          
Revisions in discount rates 5.3 0.060      
Maximum          
Disclosure of detailed information about borrowings [line items]          
Revisions in discount rates 0.084 0.090      
Decommissioning and restoration          
Disclosure of detailed information about borrowings [line items]          
Decommissioning and restoration provision 35,000,000 52,000,000      
Gas          
Disclosure of detailed information about borrowings [line items]          
Decommissioning and restoration provision 14,000,000 34,000,000      
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 194,000,000 188,000,000      
Decommissioning and restoration          
Disclosure of detailed information about borrowings [line items]          
Increase in PP&E 7,000,000 55,000,000      
Increase through change in estimated cash flows 21,000,000 (89,000,000)      
Revisions in discount rates $ 35,000,000 $ 52,000,000