Earnings Per Share

The Company’s basic earnings per share calculations are based on the weighted average number of common shares outstanding during the period. Potentially dilutive securities include outstanding stock options, restricted share units, deferred stock units and performance-based restricted share units. The effect of potentially dilutive securities is reflected in diluted earnings per common share by application of the treasury method. Diluted earnings per share gives effect to all potentially dilutive common shares outstanding during the period.



	Three Months Ended				Nine Months Ended
	September 30,				September 30,
(in millions, except per share data)	2018		2017		2018		2017
Net income attributable to common shareholders	$	97.0	$	68.2	$	246.4	$	200.5

Average basic shares outstanding	59.7		59.5		59.7		59.4
Effect of dilutive stock options	1.4		0.9		1.4		1.0
Average diluted shares outstanding	61.1		60.4		61.1		60.4

Earnings per basic share	$	1.62	$	1.15	$	4.13	$	3.38
Earnings per diluted share	$	1.59	$	1.13	$	4.04	$	3.32

The computation of diluted earnings per share excludes the effect of the potential exercise of stock options when the average market price of the common stock is lower than the exercise price of the related stock options. For the three month periods ended September 30, 2018 and 2017, the number of stock options excluded from the computation was 0.4 million and 0.6 million, respectively. For each of the nine month periods ended September 30, 2018 and 2017, the number of stock options excluded from the computation was 0.4 million.