Stock-based compensation - stock option rollforward information (Details) - Common stock including paid-in capital $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($) $ / shares shares
Number of options outstanding
Beginning balance | shares	16.3
Granted | shares	1.3
Exercised | shares	(0.7)
Forfeited | shares	(0.8)
Ending balance | shares	16.1
Weighted average exercise price per outstanding option
Beginning balance | $ / shares	$ 19.83
Granted | $ / shares	31.52
Exercised | $ / shares	16.92
Forfeited | $ / shares	20.22
Ending balance | $ / shares	$ 20.90
Other information about options outstanding
Aggregate intrinsic value | $	$ 41.2
Weighted average remaining contractual term	6 years 1 month 6 days
Information about options expected to vest and exercisable
Options expected to vest, number | shares	4.6
Options expected to vest, weighted average exercise price per option | $ / shares	$ 23.35
Options expected to vest, aggregate intrinsic value | $	$ 10.0
Options expected to vest, weighted average remaining term	7 years 10 months 24 days
Options exercisable, number | shares	11.5
Options exercisable, weighted average exercise price per option | $ / shares	$ 19.93
Options exercisable, aggregate intrinsic value | $	$ 31.2
Options exercisable, weighted average remaining term	5 years 4 months 24 days