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Employee Future Benefits - Narrative (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2023
age
Dec. 31, 2023
Dec. 31, 2023
Rate
Mar. 31, 2023
CAD ($)
Disclosure of defined benefit plans [line items]          
Weighted average duration of defined benefit obligation 10 years 4 months 24 days        
Minimum          
Disclosure of defined benefit plans [line items]          
Employer contribution (as percent)     500.00%    
Maximum          
Disclosure of defined benefit plans [line items]          
Employer contribution (as percent)     1100.00%    
Registered | Letter of credit          
Disclosure of defined benefit plans [line items]          
Letter of credit, posted         $ 88
Registered | Surety Bonds          
Disclosure of defined benefit plans [line items]          
Letter of credit, posted         $ 70
Other          
Disclosure of defined benefit plans [line items]          
Maximum age disabled and retired members eligible for benefits   65   65