Investments in Variable Interest Entities	12 Months Ended
Dec. 31, 2014
Investments in Variable Interest Entities [Abstract]
Investments in Variable Interest Entities	Investments in Variable Interest Entities Consolidated Variable Interest Entities Our consolidated financial statements include the financial results of variable interest entities in which we are the primary beneficiary. Knopp In August 2010, we entered into a license agreement with Knopp Neurosciences, Inc. (Knopp), a subsidiary of Knopp Holdings, LLC, for the development, manufacture and commercialization of dexpramipexole. Under the terms of the license agreement we made a $26.4 million upfront payment and agreed to pay Knopp development and sales-based milestone payments as well as royalties on future commercial sales. In addition, we also purchased 30.0% of the Class B common shares of Knopp for $60.0 million. Upon entering into the license agreement, we began consolidating the results of Knopp as we determined that we had the power through the license agreement to direct the activities that most significantly impacted its economic performance and were therefore its primary beneficiary. At the end of December 2012, we learned that a Phase 3 trial investigating dexpramipexole in people with amyotrophic lateral sclerosis (ALS) did not meet its primary endpoint and failed to show efficacy in its key secondary endpoints. Based on these results, we discontinued development of dexpramipexole in ALS. In 2013, we terminated our license agreement and executed our put option on our Class B common shares. We deconsolidated the results of Knopp upon termination of the license agreement. During the year ended December 31, 2012, $113.0 million of expense was reflected within our consolidated statements of income. Neurimmune SubOne AG In 2007, we entered into a collaboration agreement with Neurimmune SubOne AG (Neurimmune), a subsidiary of Neurimmune AG, for the development and commercialization of antibodies for the treatment of Alzheimer’s disease. Neurimmune conducts research to identify potential therapeutic antibodies and we are responsible for the development, manufacturing and commercialization of all products. Our anti-amyloid beta antibody, BIIB037 program, for Alzheimer’s disease resulted from this collaboration. In December 2014, we reported positive interim data from the Phase 1b trial of BIIB037. Based upon our current development plans, we may pay Neurimmune up to $335.0 million in remaining milestone payments, of which $60.0 million is due upon the initiation of a late stage clinical trial. We may also pay royalties in the low-to-mid-teens on sales of any resulting commercial products. We determined that we are the primary beneficiary of Neurimmune because we have the power through the collaboration to direct the activities that most significantly impact the entity’s economic performance and are required to fund 100% of the research and development costs incurred in support of the collaboration agreement. Accordingly, we consolidate the results of Neurimmune. Amounts that are incurred by Neurimmune for research and development expenses in support of the collaboration that we reimburse are reflected in research and development expense in our consolidated statements of income. In the second quarter of 2014, we recorded a $10.0 million milestone payment in connection with the achievement of certain clinical goals in the Phase 1 trial of our BIIB037 program for Alzheimer’s disease, which was reflected as a charge to noncontrolling interests, net of tax, within our consolidated statements of income. Future milestone payments will be reflected within our consolidated statements of income as a charge to the noncontrolling interest, net of tax, when such milestones are achieved. During the years ending December 31, 2014, 2013 and 2012, $44.1 million, $27.2 million and $13.3 million, respectively, of expense was reflected within our consolidated statements of income. The assets and liabilities of Neurimmune are not significant to our financial position or results of operations as it is a research and development organization. We have provided no financing to Neurimmune other than previously contractually required amounts. Ataxion, Inc. In February 2014, we paid $1.6 million for preferred stock of Ataxion, Inc. (Ataxion) and entered into an option agreement which gives us the right to purchase all outstanding shares of Ataxion at any time until 30 days after delivery of a Phase 1 clinical trial study report. Ataxion is a discovery-stage biopharmaceutical company developing product candidates focused on a group of orphan genetic disorders referred to as hereditary ataxias. We committed to make additional investments in Ataxion's preferred shares of up to $6.2 million if certain development milestones are achieved. In December 2014, we made an additional investment of $2.3 million in Ataxion as the first development milestone was achieved. If we exercise our option to purchase the outstanding shares of Ataxion, we could pay additional amounts upon achievement of clinical and commercial milestones. In the Ataxion relationship, through our fixed price option to purchase the company, purchases of equity and presence on the program advisory committee, we are deemed to be the primary beneficiary of Ataxion, a variable interest entity. Therefore, we consolidate the results of Ataxion. As part of the initial consolidation of Ataxion, we recorded an IPR&D intangible asset of $3.5 million and assigned that amount to minority interest within our shareholders' equity. The assets and liabilities of Ataxion are not significant to our financial position or results of operations as it is a research and development organization. We have provided no financing to Ataxion other than contractually required amounts. Unconsolidated Variable Interest Entities We have relationships with other variable interest entities that we do not consolidate as we lack the power to direct the activities that significantly impact the economic success of these entities. These relationships include investments in certain biotechnology companies. As of December 31, 2014 and 2013, the total carrying value of our investments in biotechnology companies that we have determined to be variable interest entities, but do not consolidate as we do not have the power to direct their activities, totaled $7.9 million and $5.5 million, respectively. Our maximum exposure to loss related to these variable interest entities is limited to the carrying value of our investments. We have entered into research collaborations with certain variable interest entities where we are required to fund certain development activities. These development activities are included in research and development expense within our consolidated statements of income, as they are incurred. We have provided no financing to these variable interest entities other than previously contractually required amounts.

Investments in Variable Interest Entities

Consolidated Variable Interest Entities

Our consolidated financial statements include the financial results of variable interest entities in which we are the primary beneficiary.

Knopp

In August 2010, we entered into a license agreement with Knopp Neurosciences, Inc. (Knopp), a subsidiary of Knopp Holdings, LLC, for the development, manufacture and commercialization of dexpramipexole. Under the terms of the license agreement we made a $26.4 million upfront payment and agreed to pay Knopp development and sales-based milestone payments as well as royalties on future commercial sales. In addition, we also purchased 30.0% of the Class B common shares of Knopp for $60.0 million. Upon entering into the license agreement, we began consolidating the results of Knopp as we determined that we had the power through the license agreement to direct the activities that most significantly impacted its economic performance and were therefore its primary beneficiary.

At the end of December 2012, we learned that a Phase 3 trial investigating dexpramipexole in people with amyotrophic lateral sclerosis (ALS) did not meet its primary endpoint and failed to show efficacy in its key secondary endpoints. Based on these results, we discontinued development of dexpramipexole in ALS. In 2013, we terminated our license agreement and executed our put option on our Class B common shares. We deconsolidated the results of Knopp upon termination of the license agreement.

During the year ended December 31, 2012, $113.0 million of expense was reflected within our consolidated statements of income.

Neurimmune SubOne AG

In 2007, we entered into a collaboration agreement with Neurimmune SubOne AG (Neurimmune), a subsidiary of Neurimmune AG, for the development and commercialization of antibodies for the treatment of Alzheimer’s disease. Neurimmune conducts research to identify potential therapeutic antibodies and we are responsible for the development, manufacturing and commercialization of all products. Our anti-amyloid beta antibody, BIIB037 program, for Alzheimer’s disease resulted from this collaboration. In December 2014, we reported positive interim data from the Phase 1b trial of BIIB037. Based upon our current development plans, we may pay Neurimmune up to $335.0 million in remaining milestone payments, of which $60.0 million is due upon the initiation of a late stage clinical trial. We may also pay royalties in the low-to-mid-teens on sales of any resulting commercial products.

We determined that we are the primary beneficiary of Neurimmune because we have the power through the collaboration to direct the activities that most significantly impact the entity’s economic performance and are required to fund 100% of the research and development costs incurred in support of the collaboration agreement. Accordingly, we consolidate the results of Neurimmune.

Amounts that are incurred by Neurimmune for research and development expenses in support of the collaboration that we reimburse are reflected in research and development expense in our consolidated statements of income. In the second quarter of 2014, we recorded a $10.0 million milestone payment in connection with the achievement of certain clinical goals in the Phase 1 trial of our BIIB037 program for Alzheimer’s disease, which was reflected as a charge to noncontrolling interests, net of tax, within our consolidated statements of income. Future milestone payments will be reflected within our consolidated statements of income as a charge to the noncontrolling interest, net of tax, when such milestones are achieved. During the years ending December 31, 2014, 2013 and 2012, $44.1 million, $27.2 million and $13.3 million, respectively, of expense was reflected within our consolidated statements of income.

The assets and liabilities of Neurimmune are not significant to our financial position or results of operations as it is a research and development organization. We have provided no financing to Neurimmune other than previously contractually required amounts.

Ataxion, Inc.

In February 2014, we paid $1.6 million for preferred stock of Ataxion, Inc. (Ataxion) and entered into an option agreement which gives us the right to purchase all outstanding shares of Ataxion at any time until 30 days after delivery of a Phase 1 clinical trial study report. Ataxion is a discovery-stage biopharmaceutical company developing product candidates focused on a group of orphan genetic disorders referred to as hereditary ataxias. We committed to make additional investments in Ataxion's preferred shares of up to $6.2 million if certain development milestones are achieved. In December 2014, we made an additional investment of $2.3 million in Ataxion as the first development milestone was achieved. If we exercise our option to purchase the outstanding shares of Ataxion, we could pay additional amounts upon achievement of clinical and commercial milestones.

In the Ataxion relationship, through our fixed price option to purchase the company, purchases of equity and presence on the program advisory committee, we are deemed to be the primary beneficiary of Ataxion, a variable interest entity. Therefore, we consolidate the results of Ataxion. As part of the initial consolidation of Ataxion, we recorded an IPR&D intangible asset of $3.5 million and assigned that amount to minority interest within our shareholders' equity.

The assets and liabilities of Ataxion are not significant to our financial position or results of operations as it is a research and development organization. We have provided no financing to Ataxion other than contractually required amounts.

Unconsolidated Variable Interest Entities

We have relationships with other variable interest entities that we do not consolidate as we lack the power to direct the activities that significantly impact the economic success of these entities. These relationships include investments in certain biotechnology companies.

As of December 31, 2014 and 2013, the total carrying value of our investments in biotechnology companies that we have determined to be variable interest entities, but do not consolidate as we do not have the power to direct their activities, totaled $7.9 million and $5.5 million, respectively. Our maximum exposure to loss related to these variable interest entities is limited to the carrying value of our investments.

We have entered into research collaborations with certain variable interest entities where we are required to fund certain development activities. These development activities are included in research and development expense within our consolidated statements of income, as they are incurred. We have provided no financing to these variable interest entities other than previously contractually required amounts.