Other comprehensive income (loss) and Accumulated other comprehensive income (loss) - Changes in Accumulated Other Comprehensive Loss by Component (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 41,492
Other comprehensive income (loss) before reclassifications	3,258	$ (741)
Amounts reclassified from AOCI	40	32
Net of tax amount	3,298	(709)	$ 2,194
Ending balance	47,892	41,492
Accumulated other comprehensive (loss) income
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(618)	91
Ending balance	2,680	(618)	91
Foreign currency net of hedging activities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	837	1,505
Other comprehensive income (loss) before reclassifications	2,576	(668)
Amounts reclassified from AOCI	0	0
Net of tax amount	2,576	(668)
Ending balance	3,413	837	1,505
Derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	5	0
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from AOCI	5	5
Net of tax amount	5	5
Ending balance	10	5	0
Pension and post- retirement defined benefit plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,463)	(1,410)
Other comprehensive income (loss) before reclassifications	690	(79)
Amounts reclassified from AOCI	35	26
Net of tax amount	725	(53)
Ending balance	(738)	(1,463)	(1,410)
Equity accounted investments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	3	(4)
Other comprehensive income (loss) before reclassifications	(8)	6
Amounts reclassified from AOCI	0	1
Net of tax amount	(8)	7
Ending balance	$ (5)	$ 3	$ (4)