Share Plans (Tables)

12 Months Ended

Dec. 31, 2017

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 [Table Text Block]

Total share-based compensation expense for 2017, 2016 and 2015 was as follows:

	December 31
In millions	2017		2016		2015
Restricted stock units	$	17.5	$	17.3	$	21.6
Stock options	10.5		10.4		11.4
Performance share units	11.6		6.5		—
Total share-based compensation expense	$	39.6	$	34.2	$	33.0

Stock Option Activity

The following table summarizes stock option activity under all plans for the year ended December 31, 2017:

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, 2017	5.7		$	45.72
Granted	0.9		59.09
Exercised	(1.2	)	37.00
Forfeited	(0.2	)	60.03
Expired	—		—
Outstanding as of December 31, 2017	5.2		$	49.49	5.5	$	113.7
Options exercisable as of December 31, 2017	3.4		$	46.00	4.0	$	87.5
Options expected to vest as of December 31, 2017	1.8		$	56.13	8.3	$	25.8

Stock Option Fair Value Assumptions

We estimated the fair value of each stock option award on the date of grant using a Black-Scholes option pricing model, modified for dividends and using the following weighted average assumptions:

	December 31
	2017		2016		2015
Risk-free interest rate	1.65	%	1.56	%	1.60	%
Expected dividend yield	2.35	%	2.49	%	1.97	%
Expected share price volatility	26.9	%	27.3	%	30.4	%
Expected term (years)	6.3		5.9		6.0

Restricted Stock Activity

The following table summarizes restricted stock unit activity under all plans for the year ended December 31, 2017:

Shares in millions	Number of shares		Weighted average grant date fair value
Outstanding as of January 1, 2017	0.7		$	55.31
Granted	0.4		61.27
Vested	(0.4	)	56.73
Forfeited	(0.1	)	54.35
Outstanding as of December 31, 2017	0.6		$	57.96

Share-based Compensation, Performance Shares Award Outstanding Activity [Table Text Block]

The following table summarizes performance share unit activity under all plans for the year ended December 31, 2017:

Shares in millions	Number of shares	Weighted average grant date fair value
Outstanding as of January 1, 2017	0.3	$	49.54
Granted	0.2	58.40
Vested	—	—
Forfeited	—	—
Outstanding as of December 31, 2017	0.5	$	53.56