EARNINGS PER COMMON SHARE

BASIC

Earnings per common share is calculated by dividing earnings attributable to common shareholders by the weighted average number of common shares outstanding. The weighted average number of common shares outstanding has been reduced by our pro-rata weighted average interest in our own common shares of 13 million for the three and nine months ended September 30, 2018 and 2017, resulting from our reciprocal investment in Noverco Inc.

DILUTED

The treasury stock method is used to determine the dilutive impact of stock options. This method assumes any proceeds from the exercise of stock options would be used to purchase common shares at the average market price during the period.

Weighted average shares outstanding used to calculate basic and diluted earnings per share are as follows:



	Three months ended September 30,		Nine months ended September 30,
	2018	2017	2018	2017
(number of common shares in millions)
Weighted average shares outstanding	1,705	1,635	1,695	1,482
Effect of dilutive options	3	7	4	8
Diluted weighted average shares outstanding	1,708	1,642	1,699	1,490

For the three months ended September 30, 2018 and 2017, 21,081,642 and 12,917,175, respectively, anti-dilutive stock options with a weighted average exercise price of $52.17 and $56.79, respectively, were excluded from the diluted earnings per common share calculation.

For the nine months ended September 30, 2018 and 2017, 27,069,810 and 13,293,044, respectively, anti-dilutive stock options with a weighted average exercise price of $50.37 and $57.50, respectively, were excluded from the diluted earnings per common share calculation.