Expected additional milestone payments when meeting certain sales threshold.

No definition available.

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Namespace Prefix:	biib_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Foreign sales required to trigger milestone.

+ References

No definition available.

+ Details

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- Definition

Intangible assets gross, excluding goodwill.

+ References

No definition available.

+ Details

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Namespace Prefix:	biib_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Definition

Milestones payments made to collaborative partners.

+ References

No definition available.

+ Details

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Namespace Prefix:	biib_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Expected total payments including upfront and milestone payments as well as the greater of an annual maintenance fee or usage-based royalty payments under the terms of collaboration agreement.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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- Definition

The amount of acquisition cost of a business combination allocated to an identifiable intangible asset that will be amortized.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141

-Paragraph 51

-Subparagraph e

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141

-Paragraph 52

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of goodwill arising from a business combination, which is the excess of the cost of the acquired entity over the amounts assigned to assets acquired and liabilities assumed.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141

-Paragraph 52

-Subparagraph c

-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.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141

-Paragraph 53

-Subparagraph d

-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.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The accumulated impairment losses related to goodwill as of the balance sheet date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (a,h)

-URI http://asc.fasb.org/extlink&oid=14024403&loc=d3e13816-109267

+ Details

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Intangible Assets and Goodwill (Details Textual) (USD $) In Millions, unless otherwise specified			3 Months Ended	12 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Sep. 30, 2011 Acorda	Dec. 31, 2012 Acorda	Mar. 08, 2012 Stromedix, Inc.	Dec. 31, 2012 VP One Protein	Dec. 31, 2011 VP One Protein
Collaborative arrangements and non-collaborative arrangement transactions
Business acquisition purchase price allocation to IPR&D					$ 219.2
Business acquisition purchase price allocation goodwill amount					48.2
Expected usage-based royalties to be earned through 2016 from license agreement						71.5
Intangible asset recognized to reflect the total of upfront and other time-based milestone payments expected to be made	4,033.2	3,807.5				25.7	19.2
Total milestone payments			25.0
Expected additional milestone payments when certain sales threshold is met				15.0
Foreign sales required to trigger milestone				100.0
Accumulated impairment losses related to goodwill	$ 0