Other Consolidated Financial Statement Detail (Details Textuals) (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Other Consolidated Financial Statement Detail (Textuals) [Abstract]
Other Current Assets	$ 26.4	$ 10.8
Other Accrued Expenses and Other	178.8	130.0
Dompe Farmaceutici Spa [Member]
Other Consolidated Financial Statement Detail (Textuals) [Abstract]
Outstanding Trade Receivables	13.3
Biogen Dompe SRL and Biogen Dompe Switzerland GmbH [Member]
Other Consolidated Financial Statement Detail (Textuals) [Abstract]
Final Upfront Amount Payable	$ 57.7

The total amount due to the entity within one year of the balance sheet date (or one operating cycle, if longer) from outside sources, including trade accounts receivable, notes and loans receivable, as well as any other types of receivables, net of allowances established for the purpose of reducing such receivables to an amount that approximates their net realizable value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 4

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 3

-Subparagraph a

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.3,4)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_ReceivablesNetCurrent
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant