Net Income Per Common Share

Basic earnings per share are computed based on the weighted average number of common shares outstanding. Diluted earnings per share are computed based on the weighted average number of common and dilutive potential common shares outstanding using the treasury stock method. The table shows calculations for basic and diluted earnings per share:



(In millions, except per share data)	Years ended December 31,
(In millions, except per share data)	2017		2016		2015
Numerator:
Net income—basic and diluted	$	1,045	$	591	$	634
Denominator:
Basic weighted-average common shares outstanding	164.2		164.5		164.0
Effect of share-based awards:
Stock options	1.1		1.1		1.0
Nonvested shares	0.7		0.9		0.6
Diluted weighted-average shares	166.0		166.5		165.6
Earnings per share:
Basic	$	6.36	$	3.59	$	3.87
Diluted	6.29		3.55		3.83
Number of anti-dilutive share-based awards	0.7		0.3		0.4

The current sources of dilution of our common shares are certain equity-based awards as discussed in Note 17, Share-Based Associate Compensation Plans. The above table includes the number of anti-dilutive share-based awards at year-end 2017, 2016 and 2015. We did not include these share-based awards in the computation of net income per common share (diluted) because their exercise would have anti-dilutive effects. Our 2017 net income and basic and diluted earnings per share were impacted by the Tax Act as discussed in Note 11, Income Taxes.