No definition available.

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Net minimum lease payments thereafter.

No definition available.

Name:	biib_NetMinimumLeasePaymentsThereafter
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Net minimum lease payments with in five year.

No definition available.

Name:	biib_NetMinimumLeasePaymentsWithInFiveYear
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Net minimum lease payments with in four year.

No definition available.

Name:	biib_NetMinimumLeasePaymentsWithInFourYear
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Net minimum lease payments with in one year.

No definition available.

Name:	biib_NetMinimumLeasePaymentsWithInOneYear
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Net minimum lease payments with in three year.

No definition available.

Name:	biib_NetMinimumLeasePaymentsWithInThreeYear
Namespace Prefix:	biib_
Data Type:	xbrli:monetaryItemType
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Net minimum lease payments with in two year.

No definition available.

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

Amount of minimum sublease rentals to be received by the seller-lessee for sale-leaseback transactions accounted for using the deposit method or as a financing.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 40

-Section 50

-Paragraph 2

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6456377&loc=d3e50824-112756

Name:	us-gaap_FutureMinimumSubleaseRentalsSaleLeasebackTransactions
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Amount of minimum sublease rentals to be received by the seller-lessee after the fifth fiscal year following the latest fiscal year for sale-leaseback transactions accounted for using the deposit method or as a financing.

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Amount of minimum sublease rentals to be received by the seller-lessee in the fifth fiscal year following the latest fiscal year for sale-leaseback transactions accounted for using the deposit method or as a financing.

Name:	us-gaap_FutureMinimumSubleaseRentalsSaleLeasebackTransactionsWithinFiveYears
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Amount of minimum sublease rentals to be received by the seller-lessee in the fourth fiscal year following the latest fiscal year for sale-leaseback transactions accounted for using the deposit method or as a financing.

Name:	us-gaap_FutureMinimumSubleaseRentalsSaleLeasebackTransactionsWithinFourYears
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Amount of minimum sublease rentals to be received by the seller-lessee in the next fiscal year following the latest fiscal year for sale-leaseback transactions accounted for using the deposit method or as a financing.

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Amount of minimum sublease rentals to be received by the seller-lessee in the third fiscal year following the latest fiscal year for sale-leaseback transactions accounted for using the deposit method or as a financing.

Name:	us-gaap_FutureMinimumSubleaseRentalsSaleLeasebackTransactionsWithinThreeYears
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Amount of minimum sublease rentals to be received by the seller-lessee in the second fiscal year following the latest fiscal year for sale-leaseback transactions accounted for using the deposit method or as a financing.

Name:	us-gaap_FutureMinimumSubleaseRentalsSaleLeasebackTransactionsWithinTwoYears
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Amount of required minimum rental payments for leases having an initial or remaining non-cancelable letter-terms in excess of one year.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 10

-Section 55

-Paragraph 40

-Subparagraph (Note 3)

-URI http://asc.fasb.org/extlink&oid=6584154&loc=d3e38371-112697

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 50

-Paragraph 2

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6453985&loc=d3e41502-112717

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Amount of required minimum rental payments maturing in the next fiscal year following the latest fiscal year for operating leases having an initial or remaining non-cancelable letter-terms in excess of one year.

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Amount of required minimum rental payments maturing in the fifth fiscal year following the latest fiscal year for operating leases having an initial or remaining non-cancelable letter-terms in excess of one year.

Name:	us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears
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Amount of required minimum rental payments maturing in the forth fiscal year following the latest fiscal year for operating leases having an initial or remaining non-cancelable letter-terms in excess of one year.

Name:	us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears
Namespace Prefix:	us-gaap_
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Amount of required minimum rental payments maturing in the third fiscal year following the latest fiscal year for operating leases having an initial or remaining non-cancelable letter-terms in excess of one year.

Name:	us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears
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Amount of required minimum rental payments maturing in the second fiscal year following the latest fiscal year for operating leases having an initial or remaining non-cancelable letter-terms in excess of one year.

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Amount of required minimum rental payments maturing after the fifth fiscal year following the latest fiscal year for operating leases having an initial or remaining non-cancelable letter-terms in excess of one year.