Condensed Consolidated Statements of Income (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Total revenues	$ 3,489.8	$ 3,131.1
Cost and expenses:
Cost of sales, excluding amortization and impairment of acquired intangible assets	602.0	446.0
Research and development	563.7	496.7
Selling, general and administrative	567.7	501.3
Loss on assets and liabilities held for sale	115.5	0.0
Amortization and impairment of acquired intangible assets	68.2	103.9
Collaboration profit (loss) sharing	58.1	42.5
Acquired in-process research and development	0.0	10.0
Loss (gain) on fair value remeasurement of contingent consideration	11.5	(5.6)
Restructuring charges	0.4	1.6
Total cost and expenses	1,987.1	1,596.4
Income from operations	1,502.7	1,534.7
Other income (expense), net	357.3	(41.0)
Income before income tax expense and equity in loss of investee, net of tax	1,860.0	1,493.7
Income tax expense	422.5	322.5
Equity in loss of investee, net of tax	28.7	0.0
Net income	1,408.8	1,171.2
Net income (loss) attributable to noncontrolling interests, net of tax	0.0	(1.7)
Net income attributable to Biogen Inc.	$ 1,408.8	$ 1,172.9
Net income per share:
Basic earnings per share attributable to Biogen Inc.	$ 7.17	$ 5.55
Diluted earnings per share attributable to Biogen Inc.	$ 7.15	$ 5.54
Weighted-average shares used in calculating:
Basic earnings per share attributable to Biogen Inc.	196.6	211.4
Diluted earnings per share attributable to Biogen Inc.	197.0	211.7
Product, net
Total revenues	$ 2,680.0	$ 2,523.5
Revenues from anti-CD20 therapeutic programs
Total revenues	517.4	443.2
Other
Total revenues	$ 292.4	$ 164.4