Litigation	6 Months Ended
Jun. 30, 2017
Loss Contingency, Information about Litigation Matters [Abstract]
Litigation	Litigation We are currently involved in various claims and legal proceedings, including the matters described below. For information as to our accounting policies relating to claims and legal proceedings, including use of estimates and contingencies, please read Note 1, Summary of Significant Accounting Policies, to our consolidated financial statements included in our 2016 Form 10-K. With respect to some loss contingencies, an estimate of the possible loss or range of loss cannot be made until management has further information, including, for example, (i) which claims, if any, will survive dispositive motion practice; (ii) information to be obtained through discovery; (iii) information as to the parties' damages claims and supporting evidence; (iv) the parties’ legal theories; and (v) the parties' settlement positions. The claims and legal proceedings in which we are involved also include challenges to the scope, validity or enforceability of the patents relating to our products, pipeline or processes, and challenges to the scope, validity or enforceability of the patents held by others. These include claims by third parties that we infringe their patents. An adverse outcome in any of these proceedings could result in one or more of the following and have a material impact on our business or consolidated results of operations and financial position: (i) loss of patent protection; (ii) inability to continue to engage in certain activities; and (iii) payment of significant damages, royalties, penalties and/or license fees to third parties. Loss Contingencies Qui Tam Litigation On July 6, 2015, a qui tam action filed on behalf of the United States and certain states was unsealed by the U.S. District Court for the District of Massachusetts. The action alleges sales and promotional activities in violation of the federal False Claims Act and state law counterparts, and seeks single and treble damages, civil penalties, interest, attorneys’ fees and costs. Our motion to dismiss is pending. The United States has not made an intervention decision. An estimate of the possible loss or range of loss cannot be made at this time. Securities Litigation We and certain current and former officers were defendants in In re Biogen Inc. Securities Litigation, filed by a shareholder on August 18, 2015, in the U.S. District Court for the District of Massachusetts. The amended complaint alleged violations of federal securities laws under 15 U.S.C. §78j(b) and §78t(a) and 17 C.F.R. §240.10b-5 and the lead plaintiff sought a declaration of the action as a class action, certification as a representative of the class and its counsel as class counsel, and an award of damages, interest and attorneys' fees. The U.S. District Court dismissed the case in 2016 and the U.S. Court of Appeals for the First Circuit affirmed the dismissal in May 2017. We and certain current and former officers are also defendants in an action filed by another shareholder on October 20, 2016, in the U.S. District Court for the District of Massachusetts related to the matter described above. The complaint alleges violations of federal securities laws under 15 U.S.C §78j(b) and §78t(a) and 17 C.F.R. §240.10b-5 and seeks a declaration of the action as a class action and an award of damages, interest and attorneys' fees. An estimate of the possible loss or range of loss cannot be made at this time. Other Matters Abbreviated New Drug Application Litigation relating to TECFIDERA In June and July 2017 we filed patent infringement actions pursuant to the Hatch-Waxman Act against parties who filed Abbreviated New Drug Applications (ANDAs) for generic versions of TECFIDERA. We have sued the following parties in the United States District Court for the District of Delaware: Amneal Pharmaceuticals LLC, Aurobindo Pharma U.S.A., Inc., Hetero USA, Inc., Impax Laboratories, Inc., Prinston Pharmaceuticals, Inc., Slayback Pharma LLC, Teva Pharmaceuticals USA, Inc., Alkem Laboratories Ltd., Cipla Limited, Glenmark Pharmaceuticals Pvt. Ltd., Lupin Atlantis Holdings SA, Macleods Pharmaceuticals, Ltd., MSN Laboratories Pvt. Ltd., Pharmathen S.A., Shipla Medicare Limited, Sun Pharma Global FZE, Torren Pharmaceuticals, Ltd., TWI Pharmaceuticals, Inc., Windlas Healthcare Pvt., Ltd., Accord Healthcare Inc., Par Pharmaceuticals, Sandoz Inc., Sawai (USA), Inc., and Zydus Pharmaceuticals (USA), Inc. We have also filed actions against Stason Pharmaceuticals, Inc. in the United States District Court for the Central District of California, Zydus Pharmaceuticals (USA), Inc. in the United States District Court for the District of New Jersey, and Mylan Pharmaceuticals in the United States District Court for the District of West Virginia. No trial has been scheduled in any of these matters. Interference Proceeding with Forward Pharma In April 2015 the U.S. Patent and Trademark Office (USPTO) declared an interference between Forward Pharma’s pending U.S. Patent Application No. 11/576,871 and our U.S. Patent No. 8,399,514 (the '514 patent). The '514 patent includes claims covering the treatment of MS with 480 mg of dimethyl fumarate as provided for in our TECFIDERA label. In March 2017 the USPTO ruled against Forward Pharma. Forward Pharma has appealed to the U.S. Court of Appeals for the Federal Circuit and the appeal is pending. For additional information regarding this matter, please read Note 6, Intangibles Assets and Goodwill, to these condensed consolidated financial statements. Inter Partes Review Petitions and Proceeding On March 22, 2016, the USPTO instituted inter partes review of the '514 patent on the petition of the Coalition for Affordable Drugs V LLC, an entity associated with a hedge fund. In March 2017 the USPTO ruled against the petitioner and in May 2017 denied its request for rehearing. European Patent Office Oppositions In June 2016 the European Patent Office (EPO) issued a written decision confirming its earlier revocation of our European patent number 2 137 537 (the '537 patent), which we have appealed. The '537 patent includes claims covering the treatment of MS with 480 mg of dimethyl fumarate as provided for in our TECFIDERA label. The EPO has scheduled a hearing for January 2018 on Biogen’s and others’ oppositions to Forward Pharma’s European Patent No. 2 801 355, which was issued in May 2015 and expires in October 2025. The settlement and license agreement that we entered with Forward Pharma in January 2017 did not resolve the issues pending in this proceeding and we and Forward Pharma intend to permit the EPO and the Technical Board of Appeal and the Enlarged Board of Appeal, as applicable, to make a final determination. For additional information regarding this matter, please read Note 6, Intangibles Assets and Goodwill, to these condensed consolidated financial statements. Patent Revocation Matter Swiss Pharma International AG filed actions in the District Court of The Hague (on January 11, 2016) and the German Patents Court (on March 3, 2016) to invalidate the Dutch and German counterparts of our European Patent Number 1 485 127 (“Administration of agents to treat inflammation”), which was issued in June 2011 and concerns administration of natalizumab (TYSABRI) to treat MS. The patent expires in February 2023. In July 2017 the District Court of The Hague ruled that the Dutch counterpart of the patent is invalid. We have a right of appeal. A hearing has been scheduled in the German action for early 2018. '755 Patent Litigation On May 28, 2010, Biogen MA Inc. (formerly Biogen Idec MA Inc.) filed a complaint in the U.S. District Court for the District of New Jersey alleging infringement by Bayer Healthcare Pharmaceuticals Inc. (Bayer) (manufacturer, marketer and seller of BETASERON and manufacturer of EXTAVIA), EMD Serono, Inc. (EMD Serono) (manufacturer, marketer and seller of REBIF), Pfizer Inc. (co-marketer of REBIF) and Novartis Pharmaceuticals Corp. (Novartis) (marketer and seller of EXTAVIA) of our U.S. Patent No. 7,588,755 ('755 Patent), which claims the use of interferon beta for immunomodulation or treating a viral condition, viral disease, cancers or tumors. The complaint seeks monetary damages, including lost profits and royalties. Bayer had previously filed a complaint against us in the same court, on May 27, 2010, seeking a declaratory judgment that it does not infringe the '755 Patent and that the patent is invalid, and seeking monetary relief in the form of attorneys' fees, costs and expenses. The court has consolidated the two lawsuits, and we refer to the two actions as the “Consolidated '755 Patent Actions.” Bayer, Pfizer, Novartis and EMD Serono have all filed counterclaims in the Consolidated '755 Patent Actions seeking declaratory judgments of patent invalidity and non-infringement, and seeking monetary relief in the form of costs and attorneys' fees, and EMD Serono and Bayer have each filed a counterclaim seeking a declaratory judgment that the '755 Patent is unenforceable based on alleged inequitable conduct. Bayer has also amended its complaint to seek such a declaration. We expect that the trial will be set for the first quarter of 2018. Government Matters We have learned that state and federal governmental authorities are investigating our sales and promotional practices and have received related subpoenas. We are cooperating with the government. On March 4, 2016, we received a subpoena from the federal government for documents relating to our relationship with non-profit organizations that provide assistance to patients taking drugs sold by Biogen. We are cooperating with the government. On July 1, 2016, we received civil investigative demands from the federal government for documents and information relating to our treatment of certain service agreements with wholesalers when calculating and reporting Average Manufacturer Prices in connection with the Medicaid Drug Rebate Program. We are cooperating with the government. On December 5, 2016, we received a subpoena from the federal government for documents relating to government price reporting, rebate payments and Biogen's co-pay assistance programs for AVONEX, TECFIDERA, TYSABRI and PLEGRIDY. We are cooperating with the government. On December 29, 2016, we received a civil investigative demand from the federal government for documents and information relating to our relationships with entities providing clinical education and reimbursement support services. We are cooperating with the government. In July 2017 we learned that the Prosecution Office of Milan is investigating our interactions with certain healthcare providers in Italy. We are cooperating with the government. Product Liability and Other Legal Proceedings We are also involved in product liability claims and other legal proceedings generally incidental to our normal business activities. While the outcome of any of these proceedings cannot be accurately predicted, we do not believe the ultimate resolution of any of these existing matters would have a material adverse effect on our business or financial condition.

Litigation

We are currently involved in various claims and legal proceedings, including the matters described below. For information as to our accounting policies relating to claims and legal proceedings, including use of estimates and contingencies, please read Note 1, Summary of Significant Accounting Policies, to our consolidated financial statements included in our 2016 Form 10-K.

With respect to some loss contingencies, an estimate of the possible loss or range of loss cannot be made until management has further information, including, for example, (i) which claims, if any, will survive dispositive motion practice; (ii) information to be obtained through discovery; (iii) information as to the parties' damages claims and supporting evidence; (iv) the parties’ legal theories; and (v) the parties' settlement positions.

The claims and legal proceedings in which we are involved also include challenges to the scope, validity or enforceability of the patents relating to our products, pipeline or processes, and challenges to the scope, validity or enforceability of the patents held by others. These include claims by third parties that we infringe their patents. An adverse outcome in any of these proceedings could result in one or more of the following and have a material impact on our business or consolidated results of operations and financial position: (i) loss of patent protection; (ii) inability to continue to engage in certain activities; and (iii) payment of significant damages, royalties, penalties and/or license fees to third parties.

Loss Contingencies

Qui Tam Litigation

On July 6, 2015, a qui tam action filed on behalf of the United States and certain states was unsealed by the U.S. District Court for the District of Massachusetts. The action alleges sales and promotional activities in violation of the federal False Claims Act and state law counterparts, and seeks single and treble damages, civil penalties, interest, attorneys’ fees and costs. Our motion to dismiss is pending. The United States has not made an intervention decision. An estimate of the possible loss or range of loss cannot be made at this time.

Securities Litigation

We and certain current and former officers were defendants in In re Biogen Inc. Securities Litigation, filed by a shareholder on August 18, 2015, in the U.S. District Court for the District of Massachusetts. The amended complaint alleged violations of federal securities laws under 15 U.S.C. §78j(b) and §78t(a) and 17 C.F.R. §240.10b-5 and the lead plaintiff sought a declaration of the action as a class action, certification as a representative of the class and its counsel as class counsel, and an award of damages, interest and attorneys' fees. The U.S. District Court dismissed the case in 2016 and the U.S. Court of Appeals for the First Circuit affirmed the dismissal in May 2017.

We and certain current and former officers are also defendants in an action filed by another shareholder on October 20, 2016, in the U.S. District Court for the District of Massachusetts related to the matter described above. The complaint alleges violations of federal securities laws under 15 U.S.C §78j(b) and §78t(a) and 17 C.F.R. §240.10b-5 and seeks a declaration of the action as a class action and an award of damages, interest and attorneys' fees. An estimate of the possible loss or range of loss cannot be made at this time.

Other Matters

Abbreviated New Drug Application Litigation relating to TECFIDERA

In June and July 2017 we filed patent infringement actions pursuant to the Hatch-Waxman Act against parties who filed Abbreviated New Drug Applications (ANDAs) for generic versions of TECFIDERA. We have sued the following parties in the United States District Court for the District of Delaware: Amneal Pharmaceuticals LLC, Aurobindo Pharma U.S.A., Inc., Hetero USA, Inc., Impax Laboratories, Inc., Prinston Pharmaceuticals, Inc., Slayback Pharma LLC, Teva Pharmaceuticals USA, Inc., Alkem Laboratories Ltd., Cipla Limited, Glenmark Pharmaceuticals Pvt. Ltd., Lupin Atlantis Holdings SA, Macleods Pharmaceuticals, Ltd., MSN Laboratories Pvt. Ltd., Pharmathen S.A., Shipla Medicare Limited, Sun Pharma Global FZE, Torren Pharmaceuticals, Ltd., TWI Pharmaceuticals, Inc., Windlas Healthcare Pvt., Ltd., Accord Healthcare Inc., Par Pharmaceuticals, Sandoz Inc., Sawai (USA), Inc., and Zydus Pharmaceuticals (USA), Inc. We have also filed actions against Stason Pharmaceuticals, Inc. in the United States District Court for the Central District of California, Zydus Pharmaceuticals (USA), Inc. in the United States District Court for the District of New Jersey, and Mylan Pharmaceuticals in the United States District Court for the District of West Virginia. No trial has been scheduled in any of these matters.

Interference Proceeding with Forward Pharma

In April 2015 the U.S. Patent and Trademark Office (USPTO) declared an interference between Forward Pharma’s pending U.S. Patent Application No. 11/576,871 and our U.S. Patent No. 8,399,514 (the '514 patent). The '514 patent includes claims covering the treatment of MS with 480 mg of dimethyl fumarate as provided for in our TECFIDERA label. In March 2017 the USPTO ruled against Forward Pharma. Forward Pharma has appealed to the U.S. Court of Appeals for the Federal Circuit and the appeal is pending. For additional information regarding this matter, please read Note 6, Intangibles Assets and Goodwill, to these condensed consolidated financial statements.

Inter Partes Review Petitions and Proceeding

On March 22, 2016, the USPTO instituted inter partes review of the '514 patent on the petition of the Coalition for Affordable Drugs V LLC, an entity associated with a hedge fund. In March 2017 the USPTO ruled against the petitioner and in May 2017 denied its request for rehearing.

European Patent Office Oppositions

In June 2016 the European Patent Office (EPO) issued a written decision confirming its earlier revocation of our European patent number 2 137 537 (the '537 patent), which we have appealed. The '537 patent includes claims covering the treatment of MS with 480 mg of dimethyl fumarate as provided for in our TECFIDERA label.

The EPO has scheduled a hearing for January 2018 on Biogen’s and others’ oppositions to Forward Pharma’s European Patent No. 2 801 355, which was issued in May 2015 and expires in October 2025. The settlement and license agreement that we entered with Forward Pharma in January 2017 did not resolve the issues pending in this proceeding and we and Forward Pharma intend to permit the EPO and the Technical Board of Appeal and the Enlarged Board of Appeal, as applicable, to make a final determination. For additional information regarding this matter, please read Note 6, Intangibles Assets and Goodwill, to these condensed consolidated financial statements.

Patent Revocation Matter

Swiss Pharma International AG filed actions in the District Court of The Hague (on January 11, 2016) and the German Patents Court (on March 3, 2016) to invalidate the Dutch and German counterparts of our European Patent Number 1 485 127 (“Administration of agents to treat inflammation”), which was issued in June 2011 and concerns administration of natalizumab (TYSABRI) to treat MS. The patent expires in February 2023. In July 2017 the District Court of The Hague ruled that the Dutch counterpart of the patent is invalid. We have a right of appeal. A hearing has been scheduled in the German action for early 2018.

'755 Patent Litigation

On May 28, 2010, Biogen MA Inc. (formerly Biogen Idec MA Inc.) filed a complaint in the U.S. District Court for the District of New Jersey alleging infringement by Bayer Healthcare Pharmaceuticals Inc. (Bayer) (manufacturer, marketer and seller of BETASERON and manufacturer of EXTAVIA), EMD Serono, Inc. (EMD Serono) (manufacturer, marketer and seller of REBIF), Pfizer Inc. (co-marketer of REBIF) and Novartis Pharmaceuticals Corp. (Novartis) (marketer and seller of EXTAVIA) of our U.S. Patent No. 7,588,755 ('755 Patent), which claims the use of interferon beta for immunomodulation or treating a viral condition, viral disease, cancers or tumors. The complaint seeks monetary damages, including lost profits and royalties. Bayer had previously filed a complaint against us in the same court, on May 27, 2010, seeking a declaratory judgment that it does not infringe the '755 Patent and that the patent is invalid, and seeking monetary relief in the form of attorneys' fees, costs and expenses. The court has consolidated the two lawsuits, and we refer to the two actions as the “Consolidated '755 Patent Actions.”

Bayer, Pfizer, Novartis and EMD Serono have all filed counterclaims in the Consolidated '755 Patent Actions seeking declaratory judgments of patent invalidity and non-infringement, and seeking monetary relief in the form of costs and attorneys' fees, and EMD Serono and Bayer have each filed a counterclaim seeking a declaratory judgment that the '755 Patent is unenforceable based on alleged inequitable conduct. Bayer has also amended its complaint to seek such a declaration. We expect that the trial will be set for the first quarter of 2018.

Government Matters

We have learned that state and federal governmental authorities are investigating our sales and promotional practices and have received related subpoenas. We are cooperating with the government.

On March 4, 2016, we received a subpoena from the federal government for documents relating to our relationship with non-profit organizations that provide assistance to patients taking drugs sold by Biogen. We are cooperating with the government.

On July 1, 2016, we received civil investigative demands from the federal government for documents and information relating to our treatment of certain service agreements with wholesalers when calculating and reporting Average Manufacturer Prices in connection with the Medicaid Drug Rebate Program. We are cooperating with the government.

On December 5, 2016, we received a subpoena from the federal government for documents relating to government price reporting, rebate payments and Biogen's co-pay assistance programs for AVONEX, TECFIDERA, TYSABRI and PLEGRIDY. We are cooperating with the government.

On December 29, 2016, we received a civil investigative demand from the federal government for documents and information relating to our relationships with entities providing clinical education and reimbursement support services. We are cooperating with the government.

In July 2017 we learned that the Prosecution Office of Milan is investigating our interactions with certain healthcare providers in Italy. We are cooperating with the government.

Product Liability and Other Legal Proceedings

We are also involved in product liability claims and other legal proceedings generally incidental to our normal business activities. While the outcome of any of these proceedings cannot be accurately predicted, we do not believe the ultimate resolution of any of these existing matters would have a material adverse effect on our business or financial condition.