Accounts Receivable (Details Textual) (USD $) In Millions, unless otherwise specified	12 Months Ended		12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2011 Biogen Dompe SRL [Member]	Sep. 06, 2011 Biogen Dompe SRL [Member]	Dec. 31, 2011 Italy [Member]	Dec. 31, 2010 Italy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable In Countries With Deteriorated Credit And Economic Conditions					$ 68.1	$ 118.0
Receivables purchased as part of acquisition			104.6	104.6
Loss recognized upon disposition			1.8
Accounts Receivable (Textual) [Abstract]
Payment terms of accounts receivable arising from product sales	Between 30 and 90 days
Minimum term for accounts receivable	30 days
Maximum term for accounts receivable	90 days
Accounts receivable outstanding for greater than one year	$ 56.0	$ 45.0