Income taxes - Summary of Major Components of Company's Income Tax Expense (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Current income tax expense (Note 6)	$ 909	$ 492	$ 526
Reversal of outside basis deferred tax (Note 11)	(7,832)	0	0
Origination and reversal of temporary differences	53	101	259
Effect of tax rate decrease	(72)	(25)	(11)
Effect of hedge of net investment in foreign subsidiaries and equity-method investees (Note 8)	(22)	59	(3)
Other	(12)	1	(3)
Total deferred income tax (recovery) expense	(7,885)	136	242
Total income tax (recovery) expense	(6,976)	628	768
(Loss) income before income tax (recovery) expense
Canada	2,359	2,236	2,899
Foreign	(5,412)	1,909	721
(Loss) income before income tax (recovery) expense	(3,053)	4,145	3,620
Current
Canada	377	333	404
Foreign	532	159	122
Total current income tax expense	909	492	526
Deferred
Canada	238	177	(179)
Foreign	(8,123)	(41)	421
Total deferred income tax (recovery) expense	(7,885)	136	242
Total income tax (recovery) expense	$ (6,976)	$ 628	$ 768