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Earnings per Share
6 Months Ended
Jun. 30, 2013
Earnings Per Share [Abstract]  
Earnings per Share
Earnings per Share
Basic and diluted earnings per share are calculated as follows:
 
For the Three Months
Ended June 30,
 
For the Six Months
Ended June 30,
(In millions)
2013
 
2012
 
2013
 
2012
Numerator:
 
 
 
 
 
 
 
Net income attributable to Biogen Idec Inc.
$
490.7

 
$
386.8

 
$
917.4

 
$
689.5

Denominator:
 
 
 
 
 
 
 
Weighted average number of common shares outstanding
237.5

 
239.0

 
237.2

 
239.4

Effect of dilutive securities:
 
 
 
 
 
 
 
Stock options and employee stock purchase plan
0.3

 
0.6

 
0.4

 
0.6

Time-vested restricted stock units
0.6

 
0.8

 
0.7

 
1.0

Market stock units
0.3

 
0.2

 
0.3

 
0.2

Dilutive potential common shares
1.2

 
1.6

 
1.4

 
1.8

Shares used in calculating diluted earnings per share
238.7

 
240.6

 
238.5

 
241.2


Amounts excluded from the calculation of net income per diluted share because their effects were anti-dilutive were insignificant.