Investments in Variable Interest Entities (Tables)

12 Months Ended

Dec. 31, 2011

Investments in Variable Interest Entities [Abstract]

Summary of activity related to collaboration with Knopp

	For the Years Ended December 31,
(In millions)	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	$	44.8	$	5.0
Biogen Idec’s share of expense reflected within our consolidated statements of income	$	54.8	$	31.4
Collaboration expense attributed to noncontrolling interests, net of tax	$	8.6	$	—

Summary of activity related to collaboration with Knopp along with an estimate of additional future development expense

(In millions)	As of December 31, 2011
Total upfront and milestone payments made to Knopp	$	36.4
Total development expense incurred by Biogen Idec, excluding upfront and milestone payments	$	49.8
Estimate of additional amounts to be incurred by us in development of dexpramipexole	$	260.0

Summary of activity related to collaboration with Neurimmune

	For the Years Ended December 31,
(In millions)	2011		2010		2009
Milestone payments made to Neurimmune	$	15.0	$	—	$	7.5
Total development expense incurred by the collaboration, excluding upfront and milestone payments	$	9.0	$	15.5	$	9.0
Biogen Idec’s share of expense reflected within our consolidated statements of income	$	24.0	$	15.5	$	16.5
Collaboration expense attributed to noncontrolling interests, net of tax	$	14.7	$	1.0	$	—

Summary of activity related to collaboration with Neurimmune along with an estimate of additional future development expense

(In millions)	As of December 31, 2011
Total upfront and milestone payments made to Neurimmune	$	35.0
Total development expense incurred by Biogen Idec, excluding upfront and milestone payments	$	40.0
Estimate of additional amounts to be incurred by us in development of the lead compound	$	800.0