Other long-term obligations - Summary of Other Long-Term Obligations (Detail) - CAD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Other Liabilities Disclosure [Abstract]
Employee retirement benefits	$ 932	$ 954
Asset retirement obligations and other environmental liabilities	2,575	2,564
Share-based incentive compensation liabilities	128	90
Operating lease liability	107	111
Other obligations	118	132
Total other long-term obligations	$ 3,860	$ 3,851