Acquisitions	12 Months Ended
Dec. 31, 2011
Acquisitions [Abstract]
Acquisitions	2. Acquisitions *Noncontrolling Interest in Joint Ventures* On September 6, 2011, we completed the purchase of the noncontrolling interest in our joint venture investments in Biogen Dompé SRL and Biogen Dompé Switzerland GmbH, our respective sales affiliates in Italy and Switzerland, from our joint venture partners, Dompé Farmaceutici SpA and Dompé International SA, respectively. This transaction was funded from our existing cash on hand and has been accounted for as the acquisition of a noncontrolling interest. The purchase price of these shares was comprised of cash payments totaling $152.9 million plus up to $42.5 million in contingent consideration payable upon the achievement of commercial and regulatory milestones using exchange rates at the time of the transaction. As these amounts reflect payments to acquire a noncontrolling interest, these payments and the accrual of a liability related to the contingent consideration were recorded as a reduction in the noncontrolling interest for these entities with the remainder to additional paid in capital. Upon acquisition, we recorded a liability of $38.8 million representing the acquisition date fair value of the contingent consideration. This amount was estimated through a valuation model that incorporates probability weighted assumptions relating to the achievement of these milestones and thus the likelihood of us making payments. Subsequent changes in the fair value of this obligation will be recognized as adjustments to contingent consideration within our consolidated statements of income. For additional information related to our valuation of this obligation, please read Note 8, Fair Value Measurements to these consolidated financial statements. In connection with our purchase of the noncontrolling interest in our joint venture investment in Biogen Dompé SRL, we entered into a credit assignment agreement with Dompé Farmaceutici SpA. Under the terms of this agreement, Dompé Farmaceutici SpA purchased all of Biogen Dompé SRL’s outstanding receivables as of June 30, 2011, adjusted for cash received through September 5, 2011, for $104.6 million. We have no retained interests in the receivables and have accounted for this transaction as a sale. The carrying value of these receivables exceeded their fair value, which was determined by management using significant inputs not observable in the market and thus represents a Level 3 fair value measurement, and accordingly we recognized a loss of $1.8 million upon their disposition. In addition, balances outstanding under Biogen Dompé SRL’s credit line from Dompé Farmaceutici SpA, as described in Note 12, Indebtedness to these consolidated financial statements, were repaid in September 2011. *Biogen Idec International Neuroscience GmbH* In December 2010, we acquired 100% of the stock of Biogen Idec International Neuroscience GmbH (BIN), formerly Panima Pharmaceuticals AG, an affiliate of Neurimmune AG. The purchase price was comprised of a $32.5 million cash payment plus up to $395.0 million in contingent consideration payable upon the achievement of development milestones. BIN is a business involved in the discovery of antibodies designed to treat neurological disorders. Upon acquisition, we recorded a liability of $81.2 million representing the acquisition date fair value of the contingent consideration. Subsequent changes in the fair value of this obligation are recognized as adjustments to contingent consideration within our consolidated statements of income. We allocated $110.9 million and $25.6 million of the total purchase price to acquired IPR&D and goodwill, respectively. The amount allocated to acquired IPR&D represented the fair value of the IPR&D programs acquired. The goodwill recognized is primarily attributable to establishing a deferred tax liability for the acquired IPR&D asset, which is not deductible for income tax purposes. For additional information related to our valuation of our contingent consideration obligation, please read Note 8, Fair Value Measurements to these consolidated financial statements. *Biogen Idec Hemophilia Inc.* In connection with our acquisition of Biogen Idec Hemophilia Inc. (BIH), formerly Syntonix Pharmaceuticals, Inc. (Syntonix), in January 2007, we agreed to pay up to an additional $80.0 million if certain milestone events associated with the development of BIH’s lead product, long-lasting recombinant Factor IX, a product for the treatment of hemophilia B, are achieved. The first $40.0 million contingent payment was achieved in the first quarter of 2010 upon initiation of patient enrollment in a registrational trial of Factor IX. We recorded this payment as a charge to acquired in-process research and development within our consolidated statement of income in 2010, in accordance with the accounting standards applicable to business combinations when we acquired BIH. An additional $20.0 million contingent payment will occur if prior to the tenth anniversary of the closing date, the FDA grants approval of a Biologic License Application for Factor IX. A second $20.0 million contingent payment will occur if prior to the tenth anniversary of the closing date, a marketing authorization is granted by the EMA for Factor IX. These payments will be capitalized as an intangible asset when the related milestones are achieved.

Acquisitions

12 Months Ended

Dec. 31, 2011

2. Acquisitions

Noncontrolling Interest in Joint Ventures

On September 6, 2011, we completed the purchase of the noncontrolling interest in our joint venture investments in Biogen Dompé SRL and Biogen Dompé Switzerland GmbH, our respective sales affiliates in Italy and Switzerland, from our joint venture partners, Dompé Farmaceutici SpA and Dompé International SA, respectively. This transaction was funded from our existing cash on hand and has been accounted for as the acquisition of a noncontrolling interest. The purchase price of these shares was comprised of cash payments totaling $152.9 million plus up to $42.5 million in contingent consideration payable upon the achievement of commercial and regulatory milestones using exchange rates at the time of the transaction. As these amounts reflect payments to acquire a noncontrolling interest, these payments and the accrual of a liability related to the contingent consideration were recorded as a reduction in the noncontrolling interest for these entities with the remainder to additional paid in capital.

Upon acquisition, we recorded a liability of $38.8 million representing the acquisition date fair value of the contingent consideration. This amount was estimated through a valuation model that incorporates probability weighted assumptions relating to the achievement of these milestones and thus the likelihood of us making payments. Subsequent changes in the fair value of this obligation will be recognized as adjustments to contingent consideration within our consolidated statements of income. For additional information related to our valuation of this obligation, please read Note 8, Fair Value Measurements to these consolidated financial statements.

In connection with our purchase of the noncontrolling interest in our joint venture investment in Biogen Dompé SRL, we entered into a credit assignment agreement with Dompé Farmaceutici SpA. Under the terms of this agreement, Dompé Farmaceutici SpA purchased all of Biogen Dompé SRL’s outstanding receivables as of June 30, 2011, adjusted for cash received through September 5, 2011, for $104.6 million. We have no retained interests in the receivables and have accounted for this transaction as a sale. The carrying value of these receivables exceeded their fair value, which was determined by management using significant inputs not observable in the market and thus represents a Level 3 fair value measurement, and accordingly we recognized a loss of $1.8 million upon their disposition.

In addition, balances outstanding under Biogen Dompé SRL’s credit line from Dompé Farmaceutici SpA, as described in Note 12, Indebtedness to these consolidated financial statements, were repaid in September 2011.

Biogen Idec International Neuroscience GmbH

In December 2010, we acquired 100% of the stock of Biogen Idec International Neuroscience GmbH (BIN), formerly Panima Pharmaceuticals AG, an affiliate of Neurimmune AG. The purchase price was comprised of a $32.5 million cash payment plus up to $395.0 million in contingent consideration payable upon the achievement of development milestones. BIN is a business involved in the discovery of antibodies designed to treat neurological disorders. Upon acquisition, we recorded a liability of $81.2 million representing the acquisition date fair value of the contingent consideration. Subsequent changes in the fair value of this obligation are recognized as adjustments to contingent consideration within our consolidated statements of income. We allocated $110.9 million and $25.6 million of the total purchase price to acquired IPR&D and goodwill, respectively. The amount allocated to acquired IPR&D represented the fair value of the IPR&D programs acquired. The goodwill recognized is primarily attributable to establishing a deferred tax liability for the acquired IPR&D asset, which is not deductible for income tax purposes. For additional information related to our valuation of our contingent consideration obligation, please read Note 8, Fair Value Measurements to these consolidated financial statements.

Biogen Idec Hemophilia Inc.

In connection with our acquisition of Biogen Idec Hemophilia Inc. (BIH), formerly Syntonix Pharmaceuticals, Inc. (Syntonix), in January 2007, we agreed to pay up to an additional $80.0 million if certain milestone events associated with the development of BIH’s lead product, long-lasting recombinant Factor IX, a product for the treatment of hemophilia B, are achieved. The first $40.0 million contingent payment was achieved in the first quarter of 2010 upon initiation of patient enrollment in a registrational trial of Factor IX. We recorded this payment as a charge to acquired in-process research and development within our consolidated statement of income in 2010, in accordance with the accounting standards applicable to business combinations when we acquired BIH.

An additional $20.0 million contingent payment will occur if prior to the tenth anniversary of the closing date, the FDA grants approval of a Biologic License Application for Factor IX. A second $20.0 million contingent payment will occur if prior to the tenth anniversary of the closing date, a marketing authorization is granted by the EMA for Factor IX. These payments will be capitalized as an intangible asset when the related milestones are achieved.