15. Earnings Per Share of Common Stock: The following table provides the computation of basic and diluted earnings per share of common stock for the three months ended March 31, 2018 and 2017.

	For the Three Months Ended
	March 31, 2018		March 31, 2017
Number of shares on which basic earnings per share is calculated:
Weighted-average shares outstanding during period	920,680,222		942,440,901
Add — Incremental shares under stock-based compensation plans	3,553,104		4,213,258
Add — Incremental shares associated with contingently issuable shares	1,176,108		1,182,047

Number of shares on which diluted earnings per share is calculated	925,409,434		947,836,207


Income from continuing operations (millions)	$	1,675	$	1,753
Income/(loss) from discontinued operations, net of tax (millions)	4		(3		)

Net income on which basic earnings per share is calculated (millions)	$	1,679	$	1,750

Income from continuing operations (millions)	$	1,675	$	1,753
Net income applicable to contingently issuable shares (millions)	—		—

Income from continuing operations on which diluted earnings per share is calculated (millions)	$	1,675	$	1,753
Income/(loss) from discontinued operations, net of tax, on which basic and diluted earnings per share is calculated (millions)	4		(3		)

Net income on which diluted earnings per share is calculated (millions)	$	1,679	$	1,750


Earnings/(loss) per share of common stock:
Assuming dilution
Continuing operations	$	1.81	$	1.85
Discontinued operations	0.00		0.00

Total	$	1.81	$	1.85

Basic
Continuing operations	$	1.82	$	1.86
Discontinued operations	0.00		0.00

Total	$	1.82	$	1.86

Stock options to purchase 16,869 shares and 17,917 shares were outstanding as of March 31, 2018 and 2017, respectively, but were not included in the computation of diluted earnings per share because the options’ exercise price during the respective period was greater than the average market price of the common shares, and, therefore, the effect would have been antidilutive.