Stock-based compensation - Stock Option Plan (Details) - Stock Option Plan - CAD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Number of options, Options outstanding (in shares)
Outstanding, January 1, Options (in shares)	6,936,830
Granted, Options (in shares)	1,346,358
Exercised, Options (in shares)	(723,276)
Forfeited, Options (in shares)	(167,724)
Outstanding, December 31, Options (in shares)	7,392,188	6,936,830
Vested or expected to vest at December 31, Options (in shares)	7,340,397
Exercisable, December 31, Options (in shares)	3,643,205
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Outstanding, January 1 (cad per share)	$ 45.04
Granted (cad per share)	87.51
Exercised (cad per share)	35.20
Forfeited (cad per share)	54.54
Outstanding at December 31 (cad per share)	53.36	$ 45.04
Vested or expected to vest as at December 31 (cad per share)	53.21
Exercisable at December 31 (cad per share)	$ 41.64
Number of options, Nonvested options (in shares)
Non-vested, Outstanding January 1, Options (in shares)	3,885,385
Granted, Options (in shares)	1,346,358
Vested, Options (in shares)	(1,315,036)
Non-vested, Forfeited, Options (in shares)	(167,724)
Non-vested, Outstanding December 31, Options (in shares)	3,748,983	3,885,385
Weighted average grant date fair value, Nonvested options
Non-vested, Outstanding, January 1 (cad per share)	$ 11.68
Non-vested, Granted (cad per share)	19.06	$ 13.80	$ 12.74
Vested (cad per share)	11.83
Non-vested, Forfeited (cad per share)	12.23
Non-vested, Outstanding, December 31 (cad per share)	$ 14.25	$ 11.68
Weighted average remaining term of vested or expected to vest options	4 years 3 months 18 days
Aggregate intrinsic value of vested or expected to vest options	$ 277