Investments in Variable Interest Entities (Tables)

12 Months Ended

Dec. 31, 2013

Investments in Variable Interest Entities [Abstract]

Summary Of Activity Related To Collaboration With Knopp

	For the Years Ended December 31,
(In millions)	2013		2012		2011
Milestone payments made to Knopp	$	—	$	—	$	10.0
Biogen Idec’s share of expense reflected within our consolidated statements of income	$	—	$	113.0	$	54.8
Collaboration expense attributed to noncontrolling interests, net of tax	$	—	$	—	$	8.6

Summary Of Activity Related To Collaboration With Neurimmune

	For the Years Ended December 31,
(In millions)	2013		2012		2011
Milestone payments made to Neurimmune	$	—	$	—	$	15.0
Biogen Idec’s share of expense reflected within our consolidated statements of income	$	27.2	$	13.3	$	24.2
Collaboration expense attributed to noncontrolling interests, net of tax	$	—	$	—	$	14.7

Summary Of Activity Related To Collaboration With Neurimmune Along With Estimate Of Additional Future Development

(In millions)	As of December 31, 2013
Total expense incurred by Biogen Idec	$	115.7
Estimate of additional amounts to be incurred by us in development of the lead compound	$	800.9