Diluted earnings per share is calculated by dividing Net income attributable to common shareholders by the weighted average number of shares of common stock outstanding, including shares to be issued upon exercise of stock options, performance share awards and restricted stock outstanding under Exelon's LTIPs considered to be common stock equivalents. The following table sets forth the components of basic and diluted earnings per share and shows the effect of these stock options, performance share awards and restricted stock on the weighted average number of shares outstanding (in millions) used in calculating diluted earnings per share:

	Three Months Ended March 31,
	2014		2013
Net income (loss) attributable to common shareholders	$	90	$	(4)

Weighted average common shares outstanding - basic		858		855
Assumed exercise and/or distributions of stock based awards		3		0

Weighted average common shares outstanding - diluted		861		855

The number of stock options not included in the calculation of diluted common shares outstanding due to their antidilutive effect was approximately 18 million for the three months ended March 31, 2014. For the three months ended March 31, 2013 in which there was a net loss attributable to common shareholders, no potentially dilutive securities are included in the calculation of diluted loss per share, as inclusion of these securities would have reduced the net loss per share.

Under share repurchase programs, 35 million shares of common stock are held as treasury stock with a cost of $2.3 billion as of March 31, 2014. In 2008, Exelon management decided to defer indefinitely any share repurchases.