Collaborative and Other Relationships (Tables)

3 Months Ended

Mar. 31, 2021

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Summary of Activity Related to BAN2401 and Elenbecestat Collaboration

	For the Three Months Ended March 31,
(In millions)	2021		2020
Total development expense incurred by the collaboration related to the advancement of BAN2401 and elenbecestat	$	55.5	$	43.5
Biogen's share of BAN2401 and elenbecestat development expense reflected in research and development expense in our condensed consolidated statements of income	27.7		21.8
Total sales and marketing expense incurred by the BAN2401 collaboration	5.7		4.9
Biogen's share of BAN2401 and elenbecestat sales and marketing expense reflected in selling, general and administrative expense in our condensed consolidated statements of income	2.9		2.4

Summary of Activity Related to Aducanumab Collaboration

A summary of development and sales and marketing expense related to the Aducanumab Collaboration Agreement is as follows:

	For the Three Months Ended March 31,
(In millions)	2021		2020
Total aducanumab development expense	$	47.0	$	19.1
Biogen's share of aducanumab development expense reflected in research and development expense in our condensed consolidated statements of income	25.8		10.5
Total aducanumab sales and marketing expense incurred by the Aducanumab Collaboration Agreement	111.8		22.7
Biogen's share of aducanumab sales and marketing expense reflected in selling, general and administrative expense in our condensed consolidated statements of income	60.3		12.3