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Earnings per Share (Tables)

12 Months Ended

Dec. 31, 2018

Earnings Per Share [Abstract]

Basic and diluted earnings per share

Basic and diluted earnings per share are calculated as follows:

	For the Years Ended December 31,
(In millions)	2018				2017				2016
Numerator:
Net income attributable to Biogen Inc.	$	4,430.7			$	2,539.1			$	3,702.8
Denominator:
Weighted average number of common shares outstanding	204.9				212.6				218.4
Effect of dilutive securities:
Stock options and employee stock purchase plan	—				0.1				0.1
Time-vested restricted stock units	0.3				0.2				0.2
Market stock units	0.1				0.1				0.1
Performance stock units settled in stock	—				—				—
Dilutive potential common shares	0.4				0.4				0.4
Shares used in calculating diluted earnings per share	205.3				213.0				218.8

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- References

No definition available.

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- Definition

Tabular disclosure of an entity's basic and diluted earnings per share calculations, including a reconciliation of numerators and denominators of the basic and diluted per-share computations for income from continuing operations.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

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