XML 165 R83.htm IDEA: XBRL DOCUMENT
v3.22.4

Derivative Instruments - Summary of Unrealized Gain (Loss) on Derivative Instruments Included in AOCI (Details) - Foreign Exchange Forward - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Unrealized gains | $ 29.9 | $ 60.8 | $ 0.0
Unrealized (losses) | (21.3) | (7.0) | (212.5)
Net unrealized gains (losses) | $ 8.6 | $ 53.8 | $ (212.5)

X
- Definition Unrealized Gain on Derivatives + References No definition available. + Details
Name: | biib_UnrealizedGainOnDerivatives
Namespace Prefix: | biib_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Unrealized Loss on Derivatives + References No definition available. + Details
Name: | biib_UnrealizedLossOnDerivatives
Namespace Prefix: | biib_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_DerivativeInstrumentsGainLossLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3602-108585 + Details
Name: | us-gaap_UnrealizedGainLossOnDerivatives
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForeignExchangeForwardMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |