Income taxes - Summary of Major Components of Company's Income Tax Expense (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Current income tax expense	$ 1,031	$ 909	$ 492
Reversal of outside basis deferred income tax (Note 10)	0	(7,832)	0
Origination and reversal of temporary differences	65	53	101
Effect of tax rate decrease	(70)	(72)	(25)
Effect of hedge of net investment in foreign subsidiaries and equity-method investees (Note 8)	36	(22)	59
Other	(3)	(12)	1
Total deferred income tax expense (recovery)	28	(7,885)	136
Total income tax expense (recovery)	1,059	(6,976)	628
Income (loss) before income tax expense (recovery)
Canada	2,426	2,359	2,236
Foreign	2,346	(5,412)	1,909
Income (loss) before income tax expense (recovery)	4,772	(3,053)	4,145
Current
Canada	409	377	333
Foreign	622	532	159
Total current income tax expense	1,031	909	492
Deferred
Canada	206	238	177
Foreign	(178)	(8,123)	(41)
Total deferred income tax expense (recovery)	28	(7,885)	136
Total income tax expense (recovery)	$ 1,059	$ (6,976)	$ 628