Financial and derivative instruments - Summary of estimated fair value of financial instruments (Detail) - CAD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Assets
Derivative Asset	$ 77	$ 46
Liabilities
Derivative liabilities	114	47
Effect of counterparty netting
Assets
Derivative Asset	(50)	(16)
Liabilities
Derivative liabilities	(50)	(16)
Effect of collateral netting
Assets
Derivative Asset	0	(12)
Liabilities
Derivative liabilities	(4)	0
Net carrying value
Assets
Derivative Asset	27	18
Liabilities
Derivative liabilities	60	31
Level 1
Assets
Derivative Asset	50	28
Liabilities
Derivative liabilities	54	16
Level 2
Assets
Derivative Asset	27	18
Liabilities
Derivative liabilities	60	31
Level 3
Assets
Derivative Asset	0	0
Liabilities
Derivative liabilities	$ 0	$ 0