Consolidated Statements of Income - USD ($) shares in Millions, $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Total Revenues	$ 13,452.9	$ 12,273.9	$ 11,448.8
Cost and expenses:
Cost of sales, excluding amortization and impairment of acquired intangible assets	1,816.3	1,630.0	1,478.7
Research and development	2,597.2	2,253.6	1,973.3
Selling, general and administrative	2,106.3	1,933.9	1,946.6
Amortization and impairment of acquired intangible assets	747.3	814.7	385.6
Collaboration profit (loss) sharing	185.0	112.3	10.2
Acquired in-process research and development	112.5	120.0	0.0
Restructuring charges	12.0	0.9	33.1
(Gain) loss on fair value remeasurement of contingent consideration	(12.3)	62.7	14.8
TECFIDERA litigation settlement charge	0.0	0.0	454.8
Total cost and expenses	7,564.3	6,928.1	6,297.1
Income from operations	5,888.6	5,345.8	5,151.7
Other income (expense), net	11.0	(217.0)	(218.7)
Income before income tax expense and equity in loss of investee, net of tax	5,899.6	5,128.8	4,933.0
Income tax expense	1,425.6	2,458.7	1,237.3
Equity in loss of investee, net of tax	0.0	0.0	0.0
Net income	4,474.0	2,670.1	3,695.7
Net income (loss) attributable to noncontrolling interests, net of tax	43.3	131.0	(7.1)
Net income attributable to Biogen Inc.	$ 4,430.7	$ 2,539.1	$ 3,702.8
Net income per share:
Basic earnings per share attributable to Biogen Inc.	$ 21.63	$ 11.94	$ 16.96
Diluted earnings per share attributable to Biogen Inc.	$ 21.58	$ 11.92	$ 16.93
Weighted-average shares used in calculating:
Basic earnings per share attributable to Biogen Inc.	204.9	212.6	218.4
Diluted earnings per share attributable to Biogen Inc.	205.3	213.0	218.8
Product, net
Total Revenues	$ 10,886.8	$ 10,354.7	$ 9,817.9
Revenues from anti-cd20 therapeutic programs
Total Revenues	1,980.2	1,559.2	1,314.5
Other revenue
Total Revenues	$ 585.9	$ 360.0	$ 316.4

Amortization and Impairment of Acquired Intangible Assets

No definition available.

Name:	biib_AmortizationandImpairmentofAcquiredIntangibleAssets
Namespace Prefix:	biib_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Payments are made to Elan for their share of rest of world net operating profits to effect an equal sharing of collaboration operating profit. These payments include the reimbursement of our portion of third-party royalties that Elan pays on behalf of the collaboration, relating to sales outside of the U.S. These amounts are reflected in the collaboration profit sharing line in our consolidated statement of income. As sales of TYSABRI outside the U.S. increase, our collaboration profit sharing expense will increase.

+ References

No definition available.