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Employee Future Benefits - Sensitivity Analysis (Details)
$ in Millions
Dec. 31, 2022
CAD ($)
1% decrease in the discount rate  
Disclosure of sensitivity analysis for actuarial assumptions [line items]  
Percentage of reasonably possible increase in actuarial assumption (as percent) 1.00%
1% increase in the salary scale  
Disclosure of sensitivity analysis for actuarial assumptions [line items]  
Percentage of reasonably possible increase in actuarial assumption (as percent) 1.00%
1% increase in the health-care cost trend rate  
Disclosure of sensitivity analysis for actuarial assumptions [line items]  
Percentage of reasonably possible increase in actuarial assumption (as percent) 1.00%
10% improvement in mortality rates  
Disclosure of sensitivity analysis for actuarial assumptions [line items]  
Percentage of reasonably possible increase in actuarial assumption (as percent) 10.00%
Registered Pension Plan | Canada | 1% decrease in the discount rate  
Disclosure of sensitivity analysis for actuarial assumptions [line items]  
Increase in defined benefit obligation $ 31
Registered Pension Plan | Canada | 1% increase in the salary scale  
Disclosure of sensitivity analysis for actuarial assumptions [line items]  
Increase in defined benefit obligation 1
Registered Pension Plan | Canada | 1% increase in the health-care cost trend rate  
Disclosure of sensitivity analysis for actuarial assumptions [line items]  
Increase in defined benefit obligation 0
Registered Pension Plan | Canada | 10% improvement in mortality rates  
Disclosure of sensitivity analysis for actuarial assumptions [line items]  
Increase in defined benefit obligation 12
Registered Pension Plan | US | 1% decrease in the discount rate  
Disclosure of sensitivity analysis for actuarial assumptions [line items]  
Increase in defined benefit obligation 2
Registered Pension Plan | US | 1% increase in the salary scale  
Disclosure of sensitivity analysis for actuarial assumptions [line items]  
Increase in defined benefit obligation 0
Registered Pension Plan | US | 1% increase in the health-care cost trend rate  
Disclosure of sensitivity analysis for actuarial assumptions [line items]  
Increase in defined benefit obligation 0
Registered Pension Plan | US | 10% improvement in mortality rates  
Disclosure of sensitivity analysis for actuarial assumptions [line items]  
Increase in defined benefit obligation 1
Supplemental | Canada | 1% decrease in the discount rate  
Disclosure of sensitivity analysis for actuarial assumptions [line items]  
Increase in defined benefit obligation 10
Supplemental | Canada | 1% increase in the salary scale  
Disclosure of sensitivity analysis for actuarial assumptions [line items]  
Increase in defined benefit obligation 0
Supplemental | Canada | 1% increase in the health-care cost trend rate  
Disclosure of sensitivity analysis for actuarial assumptions [line items]  
Increase in defined benefit obligation 0
Supplemental | Canada | 10% improvement in mortality rates  
Disclosure of sensitivity analysis for actuarial assumptions [line items]  
Increase in defined benefit obligation 2
Other | Canada | 1% decrease in the discount rate  
Disclosure of sensitivity analysis for actuarial assumptions [line items]  
Increase in defined benefit obligation 2
Other | Canada | 1% increase in the salary scale  
Disclosure of sensitivity analysis for actuarial assumptions [line items]  
Increase in defined benefit obligation 0
Other | Canada | 1% increase in the health-care cost trend rate  
Disclosure of sensitivity analysis for actuarial assumptions [line items]  
Increase in defined benefit obligation 1
Other | Canada | 10% improvement in mortality rates  
Disclosure of sensitivity analysis for actuarial assumptions [line items]  
Increase in defined benefit obligation $ 0