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-Name Statement of Financial Accounting Standard (FAS)
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-Paragraph 205G
Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 44C
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-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 205G
Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 44C
-Subparagraph b
-Clause 3
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-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
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-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 44C
-Subparagraph a
-Clause 1
false1340natruenanaNo definition available.falsetruefalsefalsefalsefalsefalsefalsefalsefalsefalsehttp://biogenidec.com/role/derivativeinstrumentsdetailsfalse1falsefalsefalsefalse00falsefalsefalse2falsefalsefalsefalse00falsefalsefalse3falsefalsefalsefalse00falsefalsefalse4falsefalsefalsefalse00falsefalsefalse5falsefalsefalsefalse00falsefalsefalse6falsefalsefalsefalse00falsefalsefalsefalse25USDtruefalsefalsefalseAccrued Expenses and Other Liabilities [Member]us-gaap_DerivativesFairValueByBalanceSheetLocationAxisxbrldihttp://xbrl.org/2006/xbrldibiib_AccruedExpensesAndOtherLiabilitiesMemberus-gaap_DerivativesFairValueByBalanceSheetLocationAxisexplicitMemberUSDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170$false26USDtruefalsefalsefalseAccrued Expenses and Other Liabilities [Member]us-gaap_DerivativesFairValueByBalanceSheetLocationAxisxbrldihttp://xbrl.org/2006/xbrldibiib_AccruedExpensesAndOtherLiabilitiesMemberus-gaap_DerivativesFairValueByBalanceSheetLocationAxisexplicitMemberUSDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170$naNo definition available.No authoritative reference available.false1372us-gaap_DerivativeInstrumentsInStatementOfFinancialPositionFairValueAbstractus-gaaptruenadurationNo definition available.falsefalsefalsefalsefalsetruefalsefalsefalsefalsefalseverboselabelfalse1falsefalsefalsefalse00falsefalsefalse2falsefalsefalsefalse00falsefalsefalse3falsefalsefalsefalse00falsefalsefalse4falsefalsefalsefalse00falsefalsefalse5falsefalsefalsefalse00falsefalsefalse6falsefalsefalsefalse00falsefalsefalsexbrli:stringItemTypestringNo definition available.false1392us-gaap_DerivativeLiabilityDesignatedAsHedgingInstrumentFairValueus-gaaptruecreditinstantNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truetruefalsefalse1650000016.5falsefalsefalse2falsefalsefalsefalse00falsefalsefalse3falsefalsefalsefalse00falsefalsefalse4falsefalsefalsefalse00falsefalsefalse5falsefalsefalsefalse00falsefalsefalse6truetruefalsefalse98000009.8falsefalsefalsexbrli:monetaryItemTypemonetaryFair value of a derivative liability (or nonderivative instrument) that is designated and qualifies as a hedging instrument, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 205G
Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 44C
-Subparagraph a
-Clause 1
false632falseHundredThousandsUnKnownUnKnownfalsetrue