Equity

9 Months Ended

Sep. 30, 2011

Equity and Comprehensive Income [Abstract]

Equity

12.   Equity

Total equity as of September 30, 2011 increased $784.2 million compared to December 31, 2010. This increase was primarily driven by net income attributable to Biogen Idec Inc. of $934.2 million and the increase in additional paid in capital resulting from the issuance of stock under our share based compensation arrangements totaling $299.5 million. These increases were offset by repurchases of our common stock totaling $386.6 million and a $187.3 million reduction in additional paid in capital and noncontrolling interests resulting from our purchase of the noncontrolling interest in the Dompé joint ventures, as described in Note 2, Acquisitions to these condensed consolidated financial statements.

Preferred Stock

In March 2011, the remaining 8,221 shares of our Series A Preferred Stock were converted into 493,260 shares of common stock by the holder pursuant to the conversion terms of the Series A Preferred Stock. As of September 30, 2011, there are no shares of preferred stock issued and outstanding.

Share Repurchase Activity

In February 2011, our Board of Directors authorized the repurchase of up to 20.0 million shares of our common stock. We expect to use this repurchase program principally to offset common stock issued under our share-based compensation plans. This repurchase program does not have an expiration date. Under this authorization, we repurchased approximately 5.0 million shares of our common stock at a cost of $386.6 million during the nine months ended September 30, 2011

During the nine months ended September 30, 2010, we repurchased approximately 40.3 million shares of our common stock at a cost of approximately $2.1 billion under our 2010 and 2009 stock repurchase authorizations. We retired all of these shares as they were acquired. In connection with this retirement, in accordance with our policy, we recorded a reduction in additional paid-in-capital by the same amount.