Condensed Consolidated Statements of Income (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Revenues:
Product, net	$ 2,539.6	$ 2,391.7	$ 7,315.0	$ 6,762.6
Revenues from anti-CD20 therapeutic programs	317.6	337.2	996.3	1,005.3
Other	98.6	49.0	265.5	156.6
Total revenues	2,955.8	2,777.9	8,576.8	7,924.5
Cost and expenses:
Cost of sales, excluding amortization of acquired intangible assets	416.9	310.0	1,100.2	908.6
Research and development	529.0	519.9	1,439.4	1,471.1
Selling, general and administrative	462.7	477.8	1,452.4	1,530.1
Amortization of acquired intangible assets	99.7	98.1	281.4	286.0
Restructuring charges	11.6	0.0	21.3	0.0
(Gain) loss on fair value remeasurement of contingent consideration	5.9	0.2	18.8	5.9
Collaboration profit (loss) sharing	4.7	0.0	(0.9)	0.0
Total cost and expenses	1,530.5	1,406.0	4,312.6	4,201.7
Income from operations	1,425.3	1,371.8	4,264.2	3,722.8
Other income (expense), net	(58.1)	(15.4)	(169.4)	(41.3)
Income before income tax expense and equity in loss of investee, net of tax	1,367.2	1,356.4	4,094.8	3,681.5
Income tax expense	337.0	330.1	1,047.0	904.5
Equity in loss of investee, net of tax	0.0	6.8	0.0	12.5
Net income	1,030.2	1,019.5	3,047.8	2,764.5
Net income (loss) attributable to noncontrolling interests, net of tax	(2.7)	53.9	(5.8)	49.1
Net income attributable to Biogen Inc.	$ 1,032.9	$ 965.6	$ 3,053.6	$ 2,715.4
Net income per share:
Basic earnings per share attributable to Biogen Inc.	$ 4.72	$ 4.16	$ 13.95	$ 11.60
Diluted earnings per share attributable to Biogen Inc.	$ 4.71	$ 4.15	$ 13.92	$ 11.57
Weighted-average shares used in calculating:
Basic earnings per share attributable to Biogen Inc.	218.9	232.2	219.0	234.1
Diluted earnings per share attributable to Biogen Inc.	219.4	232.6	219.4	234.7