Share-based compensation plans (Tables)

3 Months Ended

Mar. 31, 2021

Share-based Payment Arrangement [Abstract]

Compensation expense by plan

Compensation expenses are classified as selling, general and administrative expenses in the condensed consolidated statements of operations. Compensation expenses for the share-based awards were as follows:

	Compensation Expense
	Three Months Ended March 31,
(in millions)	2021		2020
Performance share units	$	5.1	4.6
Restricted stock units	1.7		1.3
Deferred stock units and fees paid in stock	0.1		0.3
Performance-based stock options	0.3		0.7
Time-based vesting stock options	0.4		0.3
Cash based awards	0.8		—
Share-based payment expense	8.4		7.2
Income tax benefit	(1.9)		(1.6)
Share-based payment expense, net of tax	$	6.5	5.6

Option activity

The following table summarizes performance-based stock option activity during the first three months of 2021:

	Shares (in thousands)	Weighted-Average Grant-Date Fair Value
Outstanding balance as of December 31, 2020	1,165.0	$	11.17
Granted	—	—
Expired(a)	(184.7)	15.23
Exercised	(33.8)	14.72
Outstanding balance as of March 31, 2021	946.5	$	10.25

(a)Although the service condition had been met, these 2018 performance options expired in accordance with the terms of the underlying award agreement.

The following table summarizes time-based stock option activity during the first three months of 2021: 

	Shares (in thousands)	Weighted-Average Grant-Date Fair Value
Outstanding balance as of December 31, 2020	207.8	$	21.38
Granted	—	—
Forfeited	—	—
Exercised	—	—
Outstanding balance as of March 31, 2021	207.8	$	21.38

Nonvested share activity

The following table summarizes RSU activity during the first three months of 2021: 

	Shares (in thousands)	Weighted-Average Grant-Date Fair Value
Nonvested balance as of December 31, 2020	251.8	$	72.30
Granted	85.6	79.02
Forfeited	(2.4)	78.33
Vested	(65.3)	77.82
Nonvested balance as of March 31, 2021	269.7	$	73.05

The following table summarizes all PSU activity during the first three months of 2021:

	Shares (in thousands)	Weighted-Average Grant-Date Fair Value
Nonvested balance as of December 31, 2020	576.7	$	80.43
Granted	266.9	81.04
Forfeited	(7.1)	78.05
Vested(a)	(149.5)	74.03
Nonvested balance as of March 31, 2021	687.0	$	82.09

(a)The vested PSUs presented are based on the target amount of the award. In accordance with the terms of the underlying award agreements, the actual shares earned and distributed for the performance period ended December 31, 2020 were 246.9 thousand, compared to target shares of 149.5 thousand.

The following table summarizes all DSU activity during the first three months of 2021:

	Shares (in thousands)	Weighted-Average Grant-Date Fair Value
Nonvested balance as of December 31, 2020	21.6	$	40.46
Granted	0.2	82.57
Forfeited	(3.0)	40.46
Vested	—	—
Nonvested balance as of March 31, 2021	18.8	$	40.95