Consolidated Statements of Income - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues:
Product, net	$ 9,817.9	$ 9,188.5	$ 8,203.4
Revenues from anti-CD20 therapeutic programs	1,314.5	1,339.2	1,195.4
Other	316.4	236.1	304.5
Total revenues	11,448.8	10,763.8	9,703.3
Cost and expenses:
Cost of sales, excluding amortization of acquired intangible assets	(1,478.7)	(1,240.4)	(1,171.0)
Research and development	(1,973.3)	(2,012.8)	(1,893.4)
Selling, general and administrative	(1,947.9)	(2,113.1)	(2,232.3)
Amortization of acquired intangible assets	(385.6)	(382.6)	(489.8)
Restructuring charges	(33.1)	(93.4)	0.0
Loss (gain) on fair value remeasurement of contingent consideration	14.8	30.5	(38.9)
Collaboration profit (loss) sharing	(10.2)	0.0	0.0
TECFIDERA litigation settlement and license charges	454.8	0.0	0.0
Total cost and expenses	6,298.4	5,872.8	5,747.7
Gain on sale of rights	0.0	0.0	16.8
Income from operations	5,150.4	4,891.0	3,972.4
Other income (expense), net	(217.4)	(123.7)	(25.8)
Income before income tax expense and equity in loss of investee, net of tax	4,933.0	4,767.3	3,946.6
Income tax expense	1,237.3	1,161.6	989.9
Equity in loss of investee, net of tax	0.0	12.5	15.1
Net income	3,695.7	3,593.2	2,941.6
Net (loss) income attributable to noncontrolling interests, net of tax	(7.1)	46.2	6.8
Net income attributable to Biogen Inc.	$ 3,702.8	$ 3,547.0	$ 2,934.8
Net income per share:
Basic earnings per share attributable to Biogen Inc.	$ 16.96	$ 15.38	$ 12.42
Diluted earnings per share attributable to Biogen Inc.	$ 16.93	$ 15.34	$ 12.37
Weighted-average shares used in calculating:
Basic earnings per share attributable to Biogen Inc.	218.4	230.7	236.4
Diluted earnings per share attributable to Biogen Inc.	218.8	231.2	237.2