XML 73 R51.htm IDEA: XBRL DOCUMENT
v3.24.3

Restructuring, Business Transformation and Other Cost Saving Initiatives - FIt for Growth Initiative (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2024 | Sep. 30, 2023
Restructuring Cost and Reserve [Line Items] |  |  |  |
Restructuring charges | $ 6.8 | $ 76.0 | $ 24.9 | $ 120.0
2023 Cost Saving Initiatives |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |
Severance Costs | 4.6 | 37.7 | 20.2 | 62.6
Accelerated Depreciation and Other Costs | 12.6 | 23.4 | 23.1 | 51.9
Restructuring charges | 17.2 | 61.1 | 43.3 | 114.5
Reata Integration |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |
Severance Costs | 0.7 | 21.0 | 3.2 | 21.0
Accelerated Depreciation and Other Costs | 4.5 | 0.0 | 13.8 | 0.0
Restructuring charges | 5.2 | 21.0 | 17.0 | 21.0
Selling, general and administrative | 2023 Cost Saving Initiatives |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |
Severance Costs | 0.0 | 0.0 | 0.0 | 0.0
Accelerated Depreciation and Other Costs | 9.1 | 5.9 | 12.5 | 17.4
Restructuring charges | 9.1 | 5.9 | 12.5 | 17.4
Selling, general and administrative | Reata Integration |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |
Severance Costs | 0.0 | 0.0 | 0.0 | 0.0
Accelerated Depreciation and Other Costs | 1.6 | 0.0 | 4.9 | 0.0
Restructuring charges | 1.6 | 0.0 | 4.9 | 0.0
Research and development | 2023 Cost Saving Initiatives |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |
Severance Costs | 0.0 | 0.0 | 0.0 | 0.0
Accelerated Depreciation and Other Costs | 3.5 | 0.2 | 10.6 | 0.7
Restructuring charges | 3.5 | 0.2 | 10.6 | 0.7
Research and development | Reata Integration |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |
Severance Costs | 0.0 | 0.0 | 0.0 | 0.0
Accelerated Depreciation and Other Costs | 2.9 | 0.0 | 8.9 | 0.0
Restructuring charges | 2.9 | 0.0 | 8.9 | 0.0
Restructuring charges | 2023 Cost Saving Initiatives |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |
Severance Costs | 4.6 | 37.7 | 20.2 | 62.6
Accelerated Depreciation and Other Costs | 0.0 | 17.3 | 0.0 | 33.8
Restructuring charges | 4.6 | 55.0 | 20.2 | 96.4
Restructuring charges | Reata Integration |  |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |  |
Severance Costs | 0.7 | 21.0 | 3.2 | 21.0
Accelerated Depreciation and Other Costs | 0.0 | 0.0 | 0.0 | 0.0
Restructuring charges | $ 0.7 | $ 21.0 | $ 3.2 | $ 21.0

X
- Definition Amount of other expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses associated with a discontinued operation or an asset retirement obligation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 45 -Paragraph 28 -Subparagraph (b) -SubTopic 10 -Topic 230 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482740/230-10-45-28 + Details
Name: | us-gaap_OtherRestructuringCosts
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 45 -Paragraph 28 -Subparagraph (b) -SubTopic 10 -Topic 230 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482740/230-10-45-28 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 420 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SAB Topic 5.P.4.b.1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479823/420-10-S99-2 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 420 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 3 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482047/420-10-45-3 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 420 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 5.P.3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479823/420-10-S99-1 + Details
Name: | us-gaap_RestructuringCharges
Namespace Prefix: | us-gaap_
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 Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 420 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SAB Topic 5.P.4.d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479823/420-10-S99-2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 420 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SAB Topic 5.P.4.b.1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479823/420-10-S99-2 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 420 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SAB Topic 5.P.4.b.2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479823/420-10-S99-2 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 420 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482017/420-10-50-1 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 420 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482017/420-10-50-1 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Topic 420 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482017/420-10-50-1 Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Topic 420 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482017/420-10-50-1 + Details
Name: | us-gaap_RestructuringCostAndReserveLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of expenses for special or contractual termination benefits provided to current employees involuntarily terminated under a benefit arrangement associated exit or disposal activities pursuant to an authorized plan. Excludes expenses related to one-time termination benefits, a discontinued operation or an asset retirement obligation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 45 -Paragraph 28 -Subparagraph (b) -SubTopic 10 -Topic 230 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482740/230-10-45-28 + Details
Name: | us-gaap_SeveranceCosts1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_RestructuringPlanAxis=biib_A2023CostSavingInitiativesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RestructuringPlanAxis=biib_ReataIntegrationMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IncomeStatementLocationAxis=us-gaap_SellingGeneralAndAdministrativeExpensesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IncomeStatementLocationAxis=us-gaap_ResearchAndDevelopmentExpenseMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IncomeStatementLocationAxis=us-gaap_RestructuringChargesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |