Share Plans (Tables)

12 Months Ended

Dec. 31, 2021

Share-based Payment Arrangement [Abstract]

Schedule of Compensation Cost

Total share-based compensation expense for 2021, 2020 and 2019 was as follows:

	December 31
In millions	2021		2020		2019
Restricted stock units	$	13.0	$	12.5	$	11.2
Stock options	3.4		3.0		4.5
Performance share units	13.4		4.8		5.7
Total share-based compensation expense	$	29.8	$	20.3	$	21.4

Stock Option Activity

The following table summarizes stock option activity under all plans for the year ended December 31, 2021:

Shares and intrinsic value in millions	Number of shares	Weighted- average exercise price		Weighted- average remaining contractual life (years)	Aggregate intrinsic value
Outstanding as of January 1, 2021	2.8	$	40.47
Granted	0.3	53.25
Exercised	(0.9)	38.88
Outstanding as of December 31, 2021	2.2	$	42.86	5.5	$	66.4
Options exercisable as of December 31, 2021	1.6	$	40.90	4.5	$	50.9
Options expected to vest as of December 31, 2021	0.6	$	47.83	8.0	$	14.9

Stock Option Fair Value Assumptions

We estimated the fair value of each stock option award issued in the annual share-based compensation grant using a Black-Scholes option pricing model, modified for dividends and using the following assumptions:

	December 31
	2021		2020		2019
Risk-free interest rate	0.37	%	1.61	%	2.89	%
Expected dividend yield	1.56	%	1.80	%	1.78	%
Expected share price volatility	29.60	%	24.10	%	23.30	%
Expected term (years)	6.5		6.8		6.1

Restricted Stock Activity

The following table summarizes restricted stock unit activity under all plans for the year ended December 31, 2021:

Shares in millions	Number of shares	Weighted average grant date fair value
Outstanding as of January 1, 2021	0.7	$	42.52
Granted	0.3	56.42
Vested	(0.3)	41.56
Forfeited	(0.1)	47.06
Outstanding as of December 31, 2021	0.6	$	47.78

Performance Shares Award Outstanding Activity

The following table summarizes performance share unit activity under all plans for the year ended December 31, 2021:

Shares in millions	Number of shares	Weighted average grant date fair value
Outstanding as of January 1, 2021	0.4	$	42.78
Granted	0.1	52.56
Vested	(0.1)	45.42
Outstanding as of December 31, 2021	0.4	$	45.55