Investments in Variable Interest Entities (Tables)

12 Months Ended

Dec. 31, 2012

Investments in Variable Interest Entities [Abstract]

Summary Of Activity Related To Collaboration With Knopp

	For the Years Ended December 31,
(In millions)	2012		2011		2010
Total upfront payments made to Knopp	$	—	$	—	$	26.4
Milestone payments made to Knopp	$	—	$	10.0	$	—
Total development expense incurred by the collaboration excluding upfront and milestone payments	$	96.3	$	44.8	$	5.0
Total expense incurred by the collaboration associated with commercial capabilities in preparation for the potential product launch	$	16.7	$	—	$	—
Biogen Idec’s share of expense reflected within our consolidated statements of income	$	113.0	$	54.8	$	31.4
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)	2012		2011		2010
Milestone payments made to Neurimmune	$	—	$	15.0	$	—
Total development expense incurred by the collaboration, excluding upfront and milestone payments	$	13.3	$	9.2	$	15.5
Biogen Idec’s share of expense reflected within our consolidated statements of income	$	13.3	$	24.2	$	15.5
Collaboration expense attributed to noncontrolling interests, net of tax	$	—	$	14.7	$	1.0

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

(In millions)	As of December 31, 2012
Total upfront and milestone payments made to Neurimmune	$	35.0
Total expense incurred by Biogen Idec, excluding upfront and milestone payments	$	53.5
Estimate of additional amounts to be incurred by us in development of the lead compound	$	783.1