Condensed Consolidated Statements of Income (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Total revenue	$ 2,290.5	$ 2,463.0
Cost and expenses:
Cost of sales, excluding amortization and impairment of acquired intangible assets	542.2	662.8
Research and development	452.9	570.6
Selling, general and administrative	581.5	605.0
Amortization and impairment of acquired intangible assets	78.3	50.2
Collaboration profit sharing/(loss reimbursement)	65.6	57.1
Restructuring charges	11.5	9.6
Other (income) expense, net	93.7	69.4
Total cost and expense	1,825.7	2,024.7
Income before income tax (benefit) expense	464.8	438.3
Income tax (benefit) expense	71.4	50.7
Net income	393.4	387.6
Net income (loss) attributable to noncontrolling interests, net of tax	0.0	(0.3)
Net income attributable to Biogen Inc.	$ 393.4	$ 387.9
Net income per share:
Basic earnings per share attributable to Biogen Inc.	$ 2.71	$ 2.69
Diluted earnings per share attributable to Biogen Inc.	$ 2.70	$ 2.67
Weighted-average shares used in calculating:
Basic earnings per share attributable to Biogen Inc.	145.2	144.4
Diluted earnings per share attributable to Biogen Inc.	145.9	145.2
Product, net
Total revenue	$ 1,711.9	$ 1,763.3
Revenue from anti-CD20 therapeutic programs
Total revenue	394.0	399.5
Contract manufacturing, royalty and other revenue
Total revenue	$ 184.6	$ 300.2