v3.25.4
PENSION AND POST-RETIREMENT AND POST-EMPLOYMENT BENEFITS - Summary of Pension Plan Assets Measured and Recorded at Fair Value on Recurring Basis (Details) - CAD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]      
Interest and dividend receivable excluded from fair value of pension plan assets $ 62 $ 57  
Sale of investments receivable excluded from fair value of pension plan assets 4 1  
Accruals for pension administration expense excluded from fair value of pension plan assets (5) 6  
Taxes payable excluded from pension plan assets fair value (2) 2  
Payable to participants excluded from fair value of pension plan assets 0 3  
Purchase of investments payable excluded from fair value of pension plan assets (2) 1  
Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 3,277 3,142 $ 2,769
Fair Value, Recurring      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 9,461 9,290  
Total fair value of plan liabilities 1 3  
Fair Value, Recurring | Pooled funds      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 3,277 3,142  
Fair Value, Recurring | Cash and cash equivalents      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 124 106  
Fair Value, Recurring | Short-term securities      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 182 171  
Fair Value, Recurring | Derivative instruments      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 2 1  
Fair Value, Recurring | Corporate shares - Canadian      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 102 116  
Fair Value, Recurring | Corporate shares - Foreign      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 2,991 2,942  
Fair Value, Recurring | Bonds and debentures - Canadian      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 2,677 2,717  
Fair Value, Recurring | Bonds and debentures - Foreign      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 106 95  
Fair Value, Recurring | Derivative instruments      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan liabilities 1 3  
Fair Value, Recurring | Level 1      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 2,962 2,917  
Total fair value of plan liabilities 0 0  
Fair Value, Recurring | Level 1 | Pooled funds      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 0 0  
Fair Value, Recurring | Level 1 | Cash and cash equivalents      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 124 106  
Fair Value, Recurring | Level 1 | Short-term securities      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 0 0  
Fair Value, Recurring | Level 1 | Derivative instruments      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 0 0  
Fair Value, Recurring | Level 1 | Corporate shares - Canadian      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 102 116  
Fair Value, Recurring | Level 1 | Corporate shares - Foreign      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 2,736 2,695  
Fair Value, Recurring | Level 1 | Bonds and debentures - Canadian      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 0 0  
Fair Value, Recurring | Level 1 | Bonds and debentures - Foreign      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 0 0  
Fair Value, Recurring | Level 1 | Derivative instruments      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan liabilities 0 0  
Fair Value, Recurring | Level 2      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 3,222 3,231  
Total fair value of plan liabilities 1 3  
Fair Value, Recurring | Level 2 | Pooled funds      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 0 0  
Fair Value, Recurring | Level 2 | Cash and cash equivalents      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 0 0  
Fair Value, Recurring | Level 2 | Short-term securities      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 182 171  
Fair Value, Recurring | Level 2 | Derivative instruments      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 2 1  
Fair Value, Recurring | Level 2 | Corporate shares - Canadian      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 0 0  
Fair Value, Recurring | Level 2 | Corporate shares - Foreign      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 255 247  
Fair Value, Recurring | Level 2 | Bonds and debentures - Canadian      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 2,677 2,717  
Fair Value, Recurring | Level 2 | Bonds and debentures - Foreign      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 106 95  
Fair Value, Recurring | Level 2 | Derivative instruments      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan liabilities 1 3  
Fair Value, Recurring | Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 3,277 3,142  
Total fair value of plan liabilities 0 0  
Fair Value, Recurring | Level 3 | Pooled funds      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 3,277 3,142  
Fair Value, Recurring | Level 3 | Cash and cash equivalents      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 0 0  
Fair Value, Recurring | Level 3 | Short-term securities      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 0 0  
Fair Value, Recurring | Level 3 | Derivative instruments      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 0 0  
Fair Value, Recurring | Level 3 | Corporate shares - Canadian      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 0 0  
Fair Value, Recurring | Level 3 | Corporate shares - Foreign      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 0 0  
Fair Value, Recurring | Level 3 | Bonds and debentures - Canadian      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 0 0  
Fair Value, Recurring | Level 3 | Bonds and debentures - Foreign      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan assets 0 0  
Fair Value, Recurring | Level 3 | Derivative instruments      
Defined Benefit Plan Disclosure [Line Items]      
Total fair value of plan liabilities $ 0 $ 0