v2.3.0.11
Earnings Per Share
 6 Months Ended
Jun. 30, 2011
Earnings Per Share  
Earnings Per Share

10. Earnings Per Share

Basic earnings per share is calculated by dividing net income by the weighted average number of shares outstanding during the reported period. The calculation of diluted earnings per share is similar to basic earnings per share, except that the weighted average number of shares outstanding includes the dilution from potential shares resulting from stock options and unvested restricted stock awards.

The components of basic and diluted earnings per share are as follows:

 

     Three Months Ended
June 30,		      Six Months Ended
June 30,		  
In millions, except per share amounts    2011      2010      2011      2010  

Net income available for common stockholders

    $ 103       $ 74       $ 168       $ 141   
                                   

Weighted average outstanding shares of common stock

      168.7         167.0         168.5         167.4   

Dilutive effect of employee stock options and restricted stock

      3.7         2.8         3.6         2.8   
                                   

Common stock and common stock equivalents

      172.4         169.8         172.1         170.2   
                                   

Earnings per share:

            

Basic

    $ 0.61       $ 0.44       $ 1.00       $ 0.84   

Diluted

    $ 0.60       $ 0.44       $ 0.98       $ 0.83   

Employee stock options to purchase 0.6 million shares of common stock for the six months ended June 30, 2010 were not included in the computation of diluted earnings per share because their exercise prices were greater than the average market price of the common shares for the period and, therefore, the effect would have been anti-dilutive. No stock options were excluded from the computation of diluted earnings per share for the three and six months ended June 30, 2011, or the three months ended June 30, 2010.