Earnings Per Share

12 Months Ended

Dec. 31, 2014

Earnings Per Share [Abstract]

Earnings Per Share

Earnings Per Share

Basic earnings per common share is computed by dividing net income available to common stockholders by the weighted-average number of common shares outstanding for the period. Diluted earnings per share adjusts basic earnings per common share for the effects of potentially dilutive common shares, if the effect is not anti-dilutive. Potentially dilutive common shares include the dilutive effects of shares issuable under the Stock Option and Performance Award Plan and shares issuable upon the conversion of preferred stock to common stock.

The following table reconciles the basic earnings per share computation to the diluted earnings per share computation (in millions, except share and per share amounts):

	2014		2013		2012
Net income available to common stockholders for purposes of computing basic and diluted earnings per share	$	502.4	$	351.2	$	377.1
Weighted-average number of shares outstanding (in thousands):
Basic shares	110,163		109,973		109,712
Effect of dilution	270		367		368
Diluted shares	110,433		110,340		110,080
Earnings per share:
Basic earnings per share	$	4.56	$	3.19	$	3.44
Diluted earnings per share	$	4.55	$	3.18	$	3.43
Potentially dilutive shares excluded from the calculation (in thousands):	2014		2013		2012
Stock options excluded as their inclusion would be anti-dilutive	57		57		—