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)	Three months ended September 30,				Nine months ended September 30,
(In millions except per share data)	2017		2016		2017		2016
Numerator:
Net income—basic and diluted	$	102	$	180	$	403	$	491
Denominator:
Basic weighted-average common shares outstanding	164.0		164.6		164.3		164.5
Effect of share-based awards:
Stock options	1.1		1.2		1.1		1.1
Nonvested shares	0.8		1.0		0.7		0.9
Diluted weighted-average shares	165.9		166.8		166.1		166.5
Earnings per share:
Basic	$	0.62	$	1.09	$	2.45	$	2.98
Diluted	0.61		1.08		2.42		2.95
Number of anti-dilutive share-based awards	0.6		—		0.7		0.3

The sources of dilution of our common shares are certain equity-based awards. See our 2016 Annual Report on Form 10-K, Item 8, Note 17, Share-Based Associate Compensation Plans, Page 160, for information about equity-based awards. The above table shows the number of anti-dilutive share-based awards for the three and nine months ended September 30, 2017 and 2016. 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.