Share-based compensation plans (Tables)

3 Months Ended

Mar. 31, 2018

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 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)	2018			2017
Performance Share Units	$	3.9		2.6
Market Share Units	0.1			0.1
Restricted Stock Units	1.8			1.2
Deferred Stock Units and fees paid in stock	0.2			0.2
Stock Options	0.8			0.4
Share-based payment expense	6.8			4.5
Income tax benefit	(1.6		)	(1.6	)
Share-based payment expense, net of tax	$	5.2		2.9

Nonvested share activity

The following table summarizes all DSU activity during the first three months of 2018:

	Shares (in thousands)	Weighted-Average Grant-Date Fair Value
Nonvested balance as of December 31, 2017	10.9	$	60.80
Granted	0.7	74.81
Forfeited	—	—
Vested	—	—
Nonvested balance as of March 31, 2018	11.6	$	61.74

The following table summarizes RSU activity during the first three months of 2018: 

	Shares (in thousands)		Weighted-Average Grant-Date Fair Value
Nonvested balance as of December 31, 2017	265.8		$	39.80
Granted	79.0		72.28
Forfeited	(0.5	)	51.96
Vested	(90.1	)	36.11
Nonvested balance as of March 31, 2018	254.2		$	51.18

The following table summarizes all MSU activity during the first three months of 2018: 

	Shares (in thousands)		Weighted-Average Grant-Date Fair Value
Nonvested balance as of December 31, 2017	74.2		$	30.37
Granted	—		—
Forfeited	—		—
Vested(a)	(74.2	)	30.37
Nonvested balance as of March 31, 2018	—		$	—

(a) The vested MSUs 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, 2017 were 111.3. No additional compensation expense was required to be recognized for the additional shares distributed, as the market condition was included in the $30.37 grant date fair value.

The following table summarizes all PSU activity during the first three months of 2018:

	Shares (in thousands)		Weighted-Average Grant-Date Fair Value
Nonvested balance as of December 31, 2017	671.2		$	37.26
Granted	169.7		73.48
Forfeited	—		—
Vested(a)	(137.7	)	29.17
Nonvested balance as of March 31, 2018	703.2		$	47.57

(a) The vested Prior 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, 2017 were 344.3.

Option activity

The following table summarizes performance-based stock option activity during the first three months of 2018: 

	Shares (in thousands)	Weighted-Average Grant-Date Fair Value
Outstanding balance as of December 31, 2017	879.8	$	8.04
Granted	417.6	16.73
Forfeited	—	—
Exercised	—	—
Outstanding balance as of March 31, 2018	1,297.4	$	10.83

The following table summarizes time-based stock option activity during the first three months of 2018: 

	Shares (in thousands)	Weighted-Average Grant-Date Fair Value
Outstanding balance as of December 31, 2017	40.6	$	8.66
Granted	—	—
Forfeited	—	—
Exercised	—	—
Outstanding balance as of March 31, 2018	40.6	$	8.66