Share-based compensation plans (Tables)

3 Months Ended

Mar. 31, 2019

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan

Compensation expenses for the share-based awards were as follows:

	Compensation Expense
	Three Months Ended March 31,
(in millions)	2019			2018
Performance Share Units	$	5.8		3.9
Market Share Units	—			0.1
Restricted Stock Units	2.0			1.8
Deferred Stock Units and fees paid in stock	0.3			0.2
Stock Options	1.3			0.8
Share-based payment expense	9.4			6.8
Income tax benefit	(2.2		)	(1.6	)
Share-based payment expense, net of tax	$	7.2		5.2

Option activity

The following table summarizes performance-based stock option activity during the first three months of 2019: 

	Shares (in thousands)	Weighted-Average Grant-Date Fair Value
Outstanding balance as of December 31, 2018	1,287.0	$	10.88
Granted	—	—
Forfeited	—	—
Exercised	—	—
Outstanding balance as of March 31, 2019	1,287.0	$	10.88

The following table summarizes time-based stock option activity during the first three months of 2019: 

	Shares (in thousands)	Weighted-Average Grant-Date Fair Value
Outstanding balance as of December 31, 2018	2.7	$	21.09
Granted	129.9	21.60
Forfeited	—	—
Exercised	—	—
Outstanding balance as of March 31, 2019	132.6	$	21.59

Nonvested share activity

The following table summarizes RSU activity during the first three months of 2019: 

	Shares (in thousands)		Weighted-Average Grant-Date Fair Value
Nonvested balance as of December 31, 2018	235.8		$	52.63
Granted	80.4		77.99
Forfeited	(2.9	)	64.37
Vested	(108.0	)	45.24
Nonvested balance as of March 31, 2019	205.3		$	66.28

The following table summarizes all PSU activity during the first three months of 2019:

	Shares (in thousands)		Weighted-Average Grant-Date Fair Value
Nonvested balance as of December 31, 2018	697.3		$	47.74
Granted	191.0		81.43
Forfeited	(4.0	)	63.18
Vested(a)(b)	(187.0	)	29.76
Nonvested balance as of March 31, 2019	697.3		$	61.76

(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, 2018 were 225.9.

The following table summarizes all DSU activity during the first three months of 2019:

	Shares (in thousands)		Weighted-Average Grant-Date Fair Value
Nonvested balance as of December 31, 2018	12.5		$	74.43
Granted	—		—
Forfeited	—		—
Vested	(0.7	)	74.81
Nonvested balance as of March 31, 2019	11.8		$	74.41