Investments in Variable Interest Entities	6 Months Ended
Jun. 30, 2015
Investments in Variable Interest Entities [Abstract]
Investments in Variable Interest Entities	Investments in Variable Interest Entities Consolidated Variable Interest Entities Our condensed consolidated financial statements include the financial results of variable interest entities in which we are the primary beneficiary. 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 December 2014, we reported positive interim data from the Phase 1b trial of aducanumab. 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 payable upon dosing of the first patient in a Phase 3 trial for aducanumab. We may also pay royalties in the low-to-mid-teens on sales of any resulting commercial products. 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 condensed consolidated statements of income. Future milestone payments, if any, will be reflected within our condensed consolidated statements of income as a charge to noncontrolling interest, net of tax, when such milestones are achieved. For the three and six months ended June 30, 2015, the collaboration incurred expenses totaling $35.0 million and $47.8 million, respectively, which is included in total costs and expenses within our condensed consolidated statements of income, as compared to $10.6 million and $21.7 million, respectively, in the prior year comparative periods. 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 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 June 30, 2015 and December 31, 2014, the total carrying value of our investments in biotechnology companies totaled $8.5 million and $7.9 million, respectively. Our maximum exposure to losses 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 within our condensed consolidated statements of income, as they are incurred. We have provided no financing to these variable interest entities other than previously contractually required amounts. For additional information related to our investments in variable interest entities, please read Note 19, Investments in Variable Interest Entities to our consolidated financial statements included within our 2014 Form 10-K.

Investments in Variable Interest Entities

Consolidated Variable Interest Entities

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

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 December 2014, we reported positive interim data from the Phase 1b trial of aducanumab. 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 payable upon dosing of the first patient in a Phase 3 trial for aducanumab. We may also pay royalties in the low-to-mid-teens on sales of any resulting commercial products.

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 condensed consolidated statements of income. Future milestone payments, if any, will be reflected within our condensed consolidated statements of income as a charge to noncontrolling interest, net of tax, when such milestones are achieved.

For the three and six months ended June 30, 2015, the collaboration incurred expenses totaling $35.0 million and $47.8 million, respectively, which is included in total costs and expenses within our condensed consolidated statements of income, as compared to $10.6 million and $21.7 million, respectively, in the prior year comparative periods.

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 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 June 30, 2015 and December 31, 2014, the total carrying value of our investments in biotechnology companies totaled $8.5 million and $7.9 million, respectively. Our maximum exposure to losses 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 within our condensed consolidated statements of income, as they are incurred. We have provided no financing to these variable interest entities other than previously contractually required amounts.

For additional information related to our investments in variable interest entities, please read Note 19, Investments in Variable Interest Entities to our consolidated financial statements included within our 2014 Form 10-K.