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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