Stock-based compensation (Tables)

3 Months Ended

Mar. 31, 2021

Share-based Payment Arrangement [Abstract]

Schedule of components of stock-based compensation expense

The following table presents the components of stock-based compensation expense:

(in millions)	Classification	Three months ended March 31,
		2021		2020
Stock options	Equity	$	4.6	$	3.9
RSUs	Equity	5.7		4.9
Optionholder awards	Liability	—		0.3
Other	Both	1.1		(0.7)
Total		$	11.4	$	8.4
Balance sheet classification:
Equity		$	10.8	$	9.2
Liability		0.6		(0.8)

Schedule of information about outstanding stock options

The following table presents information about outstanding stock options:

(options and intrinsic value in millions)	Number of options	Weighted average exercise price per option		Aggregate intrinsic value		Weighted average remaining term
Balance at December 31, 2020	20.0	$	18.80
Granted	1.5	27.70
Exercised	(1.0)	21.40
Forfeited	(0.1)	15.88
Balance at March 31, 2021	20.4	19.32		$	197.0	7.5 years
Expected to vest	9.0	19.80		83.2		8.6 years
Vested	11.4	18.93		113.7		6.6 years

Schedule of information about unvested RSUs

The following table presents information about unvested RSUs:

(awards in millions)	Number of awards	Weighted average grant date fair value per award
Balance at December 31, 2020	4.9	$	15.31
Granted	1.1	29.17
Vested	(0.7)	15.38
Forfeited	—	18.51
Balance at March 31, 2021	5.3	18.73