Investments in Variable Interest Entities	12 Months Ended
Dec. 31, 2015
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. The following are our significant variable interest entities. 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, aducanumab (BIIB037), for the treatment of Alzheimer’s disease resulted from this collaboration. In September 2015, we announced that the first patient had been enrolled in a Phase 3 trial for aducanumab, which triggered a $60.0 million milestone payment due to Neurimmune. As we consolidate the financial results of Neurimmune, we recognized this payment as a charge to noncontrolling interest in the third quarter of 2015. Based upon our current development plans for aducanumab, we may pay Neurimmune up to $275.0 million in remaining milestone payments. 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. During the years ending December 31, 2015, 2014 and 2013, these amounts were immaterial. Future milestone payments and royalties, if any, will be reflected in our consolidated statements of income as a charge to noncontrolling interest, net of tax, when such milestones are achieved. 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. Rodin Therapeutics, Inc. In December 2015, we paid $8.0 million for preferred stock in Rodin Therapeutics, Inc. (Rodin) and entered into an option and collaboration agreement which gives us the right to purchase all remaining outstanding shares of Rodin, at any time until 35 days after acceptance of an Investigational New Drug (IND) application by the FDA. Rodin is a discovery-stage biotechnology company developing novel therapeutics for neurological disorders. We committed to make additional investments in Rodin’s preferred shares of $4.0 million, if certain development milestones are achieved. If we exercise our option to purchase the outstanding shares of Rodin, we could pay additional amounts upon achievement of clinical and commercial milestones. Through our fixed price option to purchase Rodin, purchases of equity, our collaboration and presence on the program advisory committee and Rodin Board of Directors, we are deemed to be the primary beneficiary of Rodin, a variable interest entity. Therefore, we consolidate the results of Rodin. As part of the initial consolidation of Rodin, we recorded an IPR&D intangible asset of approximately $8.7 million and assigned approximately $10.9 million to minority interest in our stockholder's equity. The assets and liabilities of Rodin 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 Rodin 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 and research collaboration agreements. As of December 31, 2015 and 2014, the total carrying value of our investments in biotechnology companies totaled $29.2 million and $7.9 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 collaboration agreements with certain variable interest entities where we are required to fund certain development activities. These development activities are included in research and development expense in 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. The following are our significant variable interest entities.

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, aducanumab (BIIB037), for the treatment of Alzheimer’s disease resulted from this collaboration. In September 2015, we announced that the first patient had been enrolled in a Phase 3 trial for aducanumab, which triggered a $60.0 million milestone payment due to Neurimmune. As we consolidate the financial results of Neurimmune, we recognized this payment as a charge to noncontrolling interest in the third quarter of 2015. Based upon our current development plans for aducanumab, we may pay Neurimmune up to $275.0 million in remaining milestone payments. 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. During the years ending December 31, 2015, 2014 and 2013, these amounts were immaterial. Future milestone payments and royalties, if any, will be reflected in our consolidated statements of income as a charge to noncontrolling interest, net of tax, when such milestones are achieved.

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.

Rodin Therapeutics, Inc.

In December 2015, we paid $8.0 million for preferred stock in Rodin Therapeutics, Inc. (Rodin) and entered into an option and collaboration agreement which gives us the right to purchase all remaining outstanding shares of Rodin, at any time until 35 days after acceptance of an Investigational New Drug (IND) application by the FDA. Rodin is a discovery-stage biotechnology company developing novel therapeutics for neurological disorders. We committed to make additional investments in Rodin’s preferred shares of $4.0 million, if certain development milestones are achieved. If we exercise our option to purchase the outstanding shares of Rodin, we could pay additional amounts upon achievement of clinical and commercial milestones.

Through our fixed price option to purchase Rodin, purchases of equity, our collaboration and presence on the program advisory committee and Rodin Board of Directors, we are deemed to be the primary beneficiary of Rodin, a variable interest entity. Therefore, we consolidate the results of Rodin. As part of the initial consolidation of Rodin, we recorded an IPR&D intangible asset of approximately $8.7 million and assigned approximately $10.9 million to minority interest in our stockholder's equity.

The assets and liabilities of Rodin 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 Rodin 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 and research collaboration agreements.

As of December 31, 2015 and 2014, the total carrying value of our investments in biotechnology companies totaled $29.2 million and $7.9 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 collaboration agreements with certain variable interest entities where we are required to fund certain development activities. These development activities are included in research and development expense in 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.