Share-based compensation plans (Tables)

6 Months Ended

Jun. 30, 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 for the share-based awards were as follows:

	Compensation Expense					Compensation Expense
	Three Months Ended June 30,					Six Months Ended June 30,
(in millions)	2018			2017		2018			2017
Performance Share Units	$	2.7		1.9		$	6.6		4.5
Market Share Units	—			—		0.1			0.1
Restricted Stock Units	1.5			1.2		3.3			2.4
Deferred Stock Units and fees paid in stock	0.3			0.3		0.5			0.5
Stock Options	1.2			0.6		2.0			1.0
Share-based payment expense	5.7			4.0		12.5			8.5
Income tax benefit	(1.3		)	(1.5	)	(2.9		)	(3.1	)
Share-based payment expense, net of tax	$	4.4		2.5		$	9.6		5.4

Option activity

The following table summarizes time-based stock option activity during the first six 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	(37.9	)	7.77
Outstanding balance as of June 30, 2018	2.7		$	21.09

The following table summarizes performance-based stock option activity during the first six 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 June 30, 2018	1,297.4	$	10.83

Nonvested share activity

The following table summarizes all MSU activity during the first six 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 June 30, 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 RSU activity during the first six months of 2018: 

	Shares (in thousands)		Weighted-Average Grant-Date Fair Value
Nonvested balance as of December 31, 2017	265.8		$	39.80
Granted	81.8		72.33
Forfeited	(3.2	)	54.85
Vested	(94.6	)	35.83
Nonvested balance as of June 30, 2018	249.8		$	51.77

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

	Shares (in thousands)		Weighted-Average Grant-Date Fair Value
Nonvested balance as of December 31, 2017	10.9		$	60.80
Granted	12.5		74.43
Forfeited	—		—
Vested	(10.9	)	60.80
Nonvested balance as of June 30, 2018	12.5		$	74.43

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

	Shares (in thousands)		Weighted-Average Grant-Date Fair Value
Nonvested balance as of December 31, 2017	671.2		$	37.26
Granted	171.7		73.49
Forfeited	(5.4	)	49.00
Vested(a)	(137.7	)	29.17
Nonvested balance as of June 30, 2018	699.8		$	47.64

(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.