Earnings per Share

12 Months Ended

Dec. 31, 2014

Earnings Per Share [Abstract]

Earnings per Share

Earnings per Share

Basic and diluted earnings per share are calculated as follows:

	For the Years Ended December 31,
(In millions)	2014		2013		2012
Numerator:
Net income attributable to Biogen Idec Inc.	$	2,934.8	$	1,862.3	$	1,380.0
Denominator:
Weighted average number of common shares outstanding	236.4		236.9		237.9
Effect of dilutive securities:
Stock options and employee stock purchase plan	0.1		0.3		0.5
Time-vested restricted stock units	0.5		0.8		1.0
Market stock units	0.2		0.3		0.3
Dilutive potential common shares	0.8		1.4		1.8
Shares used in calculating diluted earnings per share	237.2		238.3		239.7

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

Earnings per share for the years ended December 31, 2014, 2013 and 2012, reflects, on a weighted average basis, the repurchase of 1.0 million shares, 0.9 million shares and 5.8 million shares, respectively, of our common stock under our share repurchase authorizations.