Inventory (Details 1) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Components of inventory
Total finished goods and work in process	$ 544,000,000	$ 345,600,000
Raw materials	115,000,000	101,800,000
Total inventory	659,003,000	447,373,000
AVONEX
Components of inventory
Total finished goods and work in process	176,900,000	144,000,000
TYSABRI
Components of inventory
Total finished goods and work in process	170,900,000	114,800,000
TECFIDERA
Components of inventory
Total finished goods and work in process	33,600,000	0
Other
Components of inventory
Total finished goods and work in process	$ 162,600,000	$ 86,800,000

The aggregated amount of merchandise or goods held by the entity and readily available for future sale plus items held by the entity which are partially complete or in the process of being readied for future sale. This amount is net of valuation reserves and adjustments.

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

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 5

-Section BB

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 330

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SAB TOPIC 5.BB)

-URI http://asc.fasb.org/extlink&oid=27011343&loc=d3e100047-122729

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 6

-Article 5

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.6(a)(1),(3))

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

Name:	us-gaap_InventoryFinishedGoodsAndWorkInProcessNetOfReserves
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant