v3.25.4
Accumulated other comprehensive loss (Details) - CAD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Accumulated other comprehensive loss, before tax, beginning balance $ (1,682) $ (3,075) $ (2,736)
Income tax recovery (expense), beginning balance 662 796 767
Accumulated other comprehensive loss, net of tax, beginning balance (1,020) (2,279) (1,969)
Other comprehensive income (loss) before reclassifications:      
Translation of net investment, before tax (834) 1,377 (363)
Translation of net investment, income tax recovery (expense) 0 0 0
Translation of net investment, net of tax (834) 1,377 (363)
Translation of US dollar debt, before tax 548 (989) 262
Translation of US dollar debt, income tax recovery (expense) (72) 130 (33)
Translation of US dollar debt, net of tax 476 (859) 229
Derivative instruments, before tax (46) (15) 97
Derivative instruments, income tax recovery (expense) 4 4 (25)
Derivative instruments, net of tax (42) (11) 72
Actuarial gain (loss) arising during the year, before tax 376 973 (331)
Actuarial gain (loss) arising during the year, income tax recovery (expense) (99) (255) 86
Actuarial gain (loss) arising during the year, net of tax 277 718 (245)
Amounts reclassified from Accumulated other comprehensive loss:      
Amortization of net actuarial loss, before tax 52 56  
Amortization of net actuarial loss, income tax recovery (expense) (14) (14)  
Amortization of net actuarial loss, net of tax 38 42  
Amortization of prior service credit, before tax (4) (4) (3)
Amortization of prior service credit, income tax recovery (expense) 1 0 1
Amortization of prior service credit, net of tax (3) (4) (2)
Amortization of gain on treasury lock, before tax 44 (5) (1)
Amortization of gain on treasury lock, income tax recovery (expense) (3) 1 0
Amortization of gain on treasury lock, net of tax 41 (4) (1)
Other comprehensive income (loss) before income taxes 136 1,393 (339)
Income tax recovery (expense) (183) (134) 29
Other comprehensive income (loss) (47) 1,259 (310)
Accumulated other comprehensive loss, before tax, ending balance (1,546) (1,682) (3,075)
Income tax recovery (expense), ending balance 479 662 796
Accumulated other comprehensive loss, net of tax, ending balance (1,067) (1,020) (2,279)
Treasury Lock      
Amounts reclassified from Accumulated other comprehensive loss:      
Amortization of treasury locks 4    
Foreign currency translation adjustments      
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Accumulated other comprehensive loss, before tax, beginning balance 217 (171) (70)
Other comprehensive income (loss) before reclassifications:      
Translation of net investment, before tax (834) 1,377 (363)
Translation of US dollar debt, before tax 548 (989) 262
Amounts reclassified from Accumulated other comprehensive loss:      
Other comprehensive income (loss) before income taxes (286) 388 (101)
Accumulated other comprehensive loss, before tax, ending balance (69) 217 (171)
Pension and other postretirement benefit plans      
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Accumulated other comprehensive loss, before tax, beginning balance (1,978) (3,003) (2,669)
Other comprehensive income (loss) before reclassifications:      
Actuarial gain (loss) arising during the year, before tax 376 973 (331)
Amounts reclassified from Accumulated other comprehensive loss:      
Amortization of net actuarial loss, before tax 52 56  
Amortization of prior service credit, before tax (4) (4) (3)
Other comprehensive income (loss) before income taxes 424 1,025 (334)
Accumulated other comprehensive loss, before tax, ending balance (1,554) (1,978) (3,003)
Derivative instruments      
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Accumulated other comprehensive loss, before tax, beginning balance 79 99 3
Other comprehensive income (loss) before reclassifications:      
Derivative instruments, before tax (46) (15) 97
Amounts reclassified from Accumulated other comprehensive loss:      
Amortization of gain on treasury lock, before tax 44 (5) (1)
Other comprehensive income (loss) before income taxes (2) (20) 96
Accumulated other comprehensive loss, before tax, ending balance $ 77 $ 79 $ 99