Stock-based compensation - Narrative (Details) - CAD ($) $ / shares in Units, $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024	Dec. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 34	$ 59
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options issued (in shares)	967,335
Options issued, weighted average price per share (In cad per share)	$ 110.48
Expiration period (in years)	7 years
Stock options grant date fair value	$ 28
Stock Options | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)	12 months
Stock Options | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)	48 months
Performance Share Units (PSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units issued (in shares)	594,802			415,660
Grant date fair value	$ 66
Number of trading days	30 days
Cash payout of associated shares (in shares)	381,759
Performance Share Units (PSUs) | Share-based Payment Arrangement, Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
PSU payout percentage	120.00%
Cash payout	$ 48
Performance Deferred Share Units (PDSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units issued (in shares)	24,149			13,506
Grant date fair value	$ 3
Number of units that can be granted as percentage of shares acquired	25.00%
Vested in period (in shares)			9,774
Payout in future periods			$ 2
PSUs and PDSUs | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)	3 years
PSUs and PDSUs | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)	4 years