Subsequent Events (Details) (TYSABRI product [Member], USD $) In Billions, unless otherwise specified	Apr. 02, 2013
TYSABRI product [Member]
Subsequent Event [Line Items]
Future contingent payment for the first 12 months	12.00%
Future contingent payment for annual worldwide net sales up to $2.0 billion	18.00%
Future contingent payment threshold	$ 2.0
Future contingent payment for annual worldwide net sales that exceed $2.0 billion	25.00%
Acquired Finite-lived Intangible Asset, Amount	$ 3.25

The aggregate amount assigned to a major class of finite-lived intangible assets acquired either individually or as part of a group of assets (in either an asset acquisition or business combination). A major class is composed of intangible assets that can be grouped together because they are similar, either by their nature or by their use in the operations of a company.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=7658586&loc=d3e16265-109275

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 142

-Paragraph 44

-Subparagraph a(1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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