v3.25.4
Pensions and other postretirement benefits (Derivative Financial Instruments) (Details) - Pensions - CAD ($)
Dec. 31, 2025
Dec. 31, 2024
Interest rate | Futures contracts    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Notional amount $ 259,000,000 $ 320,000,000
Asset/unrealized gain 0 0
Liability/unrealized loss 0 0
Interest rate | Bonds Forwards    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Notional amount 57,000,000 51,000,000
Asset/unrealized gain 4,000,000 2,000,000
Liability/unrealized loss (5,000,000) (2,000,000)
Interest rate | Bonds Forwards | Short    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Notional amount 154,000,000 135,000,000
Asset/unrealized gain 4,000,000 1,000,000
Liability/unrealized loss 0 0
Interest rate | Bond swaps    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Notional amount 464,000,000 353,000,000
Asset/unrealized gain 1,000,000 11,000,000
Liability/unrealized loss (3,000,000) (1,000,000)
Interest rate | Credit default swaps    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Notional amount 552,000,000 288,000,000
Asset/unrealized gain 0 0
Liability/unrealized loss (12,000,000) (6,000,000)
Foreign exchange | Futures contracts    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Notional amount 0 30,000,000
Asset/unrealized gain 0 0
Liability/unrealized loss 0 0
Foreign exchange | Forward contracts    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Notional amount 5,343,000,000 4,894,000,000
Asset/unrealized gain 63,000,000 37,000,000
Liability/unrealized loss (3,000,000) (139,000,000)
Foreign exchange | Options purchased    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Notional amount 299,000,000 286,000,000
Asset/unrealized gain 6,000,000 9,000,000
Liability/unrealized loss (1,000,000) 0
Foreign exchange | Options written    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Notional amount 81,000,000 196,000,000
Asset/unrealized gain 0 0
Liability/unrealized loss (1,000,000) (5,000,000)
Equity | Futures contracts    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Notional amount 183,000,000 166,000,000
Asset/unrealized gain 0 1,000,000
Liability/unrealized loss 0 0
Equity | Options purchased    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Notional amount 31,000,000 48,000,000
Asset/unrealized gain 10,000,000 12,000,000
Liability/unrealized loss 0 0
Equity | Options written    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Notional amount 2,000,000 0
Asset/unrealized gain 0 0
Liability/unrealized loss 0 0
Equity | Swaps    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Notional amount 1,430,000,000 2,062,000,000
Asset/unrealized gain 16,000,000 14,000,000
Liability/unrealized loss (14,000,000) (23,000,000)
Commodity | Forward contracts    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Notional amount 3,000,000 0
Asset/unrealized gain 0 0
Liability/unrealized loss 0 0
Commodity | Swaps    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Notional amount 0 37,000,000
Asset/unrealized gain 0 0
Liability/unrealized loss 0 (6,000,000)
Commodity | Index swaps    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Notional amount 195,000,000 144,000,000
Asset/unrealized gain 2,000,000 1,000,000
Liability/unrealized loss 0 (1,000,000)
Defined Benefit Plan, Derivative, Total    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Notional amount 8,899,000,000 8,875,000,000
Asset/unrealized gain 102,000,000 87,000,000
Liability/unrealized loss $ (39,000,000) $ (183,000,000)