v3.25.4

Indebtedness - 2023 Term Loan Credit Agreement (Details) - Line of Credit - USD ($) $ in Millions		1 Months Ended
	Sep. 26, 2023	Sep. 30, 2023	Jun. 30, 2024	Mar. 31, 2024
2023 Term Loan
Debt Instrument
Senior unsecured revolving credit facility maximum borrowing capacity		$ 1,500.0
Unused borrowing capacity, amount		500.0
2023 Term Loan \| Floating Rate 364-Day Tranche
Debt Instrument
Senior unsecured revolving credit facility maximum borrowing capacity				$ 150.0
Debt instrument, term	364 days
Repayments of short-term debt, maturing in more than three months	$ 350.0
2023 Term Loan \| Term Loan 2023 Three-Year Tranche
Debt Instrument
Senior unsecured revolving credit facility maximum borrowing capacity			$ 250.0
2023 Term Loan \| Reata Pharmaceuticals, Inc
Debt Instrument
Proceeds from long-term lines of credit		1,000.0
2023 Term Loan \| Reata Pharmaceuticals, Inc \| 3.625% Senior Notes due September 15, 2022
Debt Instrument
Proceeds from long-term lines of credit		500.0
2023 Term Loan \| Reata Pharmaceuticals, Inc \| 2023 Term Loan Three-Year Tranche
Debt Instrument
Proceeds from long-term lines of credit		$ 500.0
Debt instrument, term		3 years
The Credit Facility Floating Rate Three-Year Tranche \| Floating Rate 364-Day Tranche
Debt Instrument
Senior unsecured revolving credit facility maximum borrowing capacity				$ 250.0

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.

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BIOGEN INC. 10-K