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Collaborative and Other Relationships - Collaborations (Details) $ in Millions | 1 Months Ended | 3 Months Ended | 6 Months Ended
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Apr. 30, 2022 USD ($) | Aug. 31, 2021 USD ($) | Jun. 30, 2021 USD ($) | Dec. 31, 2019 product | Mar. 31, 2023 USD ($) | Jun. 30, 2022 USD ($) | Mar. 31, 2022 USD ($) | Dec. 31, 2021 USD ($) | Sep. 30, 2021 USD ($) | Jun. 30, 2021 USD ($) | Mar. 31, 2020 USD ($) | Jun. 30, 2022 USD ($) | Jun. 30, 2021 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Research and Development Expense (Excluding Acquired in Process Cost) |  |  |  |  |  | $ 528.6 |  |  |  | $ 585.1 |  | $ 1,080.3 | $ 1,099.3
Cost of sales, excluding amortization and impairment of acquired intangible assets |  |  |  |  |  | 484.0 |  |  |  | 459.7 |  | 1,237.9 | 937.8
(Gain) loss on equity method investments |  |  |  |  |  |  |  |  |  |  |  | 2.6 | 16.1
Samsung Bioepis |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
(Gain) loss on equity method investments |  |  |  |  |  | 13.0 |  |  |  | 41.6 |  | 17.0 | 30.6
Loss recorded on Samsung Bioepis joint venture |  |  |  |  |  | 5.9 |  |  |  | 34.3 |  | 2.6 | 16.1
Amortization |  |  |  |  |  | 7.1 |  |  |  | $ 7.3 |  | 14.4 | 14.5
ADUHELM |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Research and development expense |  |  |  |  |  |  |  |  |  |  |  | $ 275.0 |
Cost of sales, excluding amortization and impairment of acquired intangible assets |  |  |  |  |  | 275.0 |  |  |  |  |  |  |
ADUHELM | Maximum | Forecast |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Research and development expense |  |  |  |  | $ 335.0 |  |  |  |  |  |  |  |
Eisai |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of future development costs related to Eisai |  |  |  |  |  |  |  |  |  | 45.00% |  | 45.00% |
Collaboration agreement term |  |  |  |  |  |  | 5 years |  |  |  |  | 10 years |
Cost of Goods Sold, Capacity Charges |  |  |  |  |  |  |  |  |  |  |  | $ 45.0 |
(Gain) loss on equity method investments |  |  |  |  |  | 28.9 |  |  |  | $ 40.1 |  | 210.6 | 40.1
Due from Related Parties |  |  |  |  |  | 250.8 |  | $ 285.4 |  |  |  | 250.8 |
Due to Related Parties |  |  |  |  |  | 56.0 |  | 46.5 |  |  |  | 56.0 |
Eisai | BAN2401 and Elenbecestat |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Expense Incurred By Collaboration |  |  |  |  |  | 78.6 |  |  |  | 62.2 |  | 155.6 | 117.7
Expense reflected within statements of income |  |  |  |  |  | 39.3 |  |  |  | 31.1 |  | 77.8 | 58.8
Eisai | ADUHELM |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Expense reflected within statements of income |  |  |  |  |  | 0.0 |  |  |  | 45.0 |  | 0.0 | 45.0
Additional milestone payment |  |  | $ 100.0 |  |  | 0.0 |  |  |  | 100.0 |  | $ 0.0 | 100.0
(Gain) loss on equity method investments |  |  |  |  |  | 160.0 |  | 59.0 | $ 45.0 | 45.0 |  |  |
Samsung Bioepis |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Upfront and milestone payments made to collaborative partner |  |  |  |  |  |  |  |  |  |  | $ 100.0 |  |
Collaboration agreement term |  |  |  |  |  |  |  |  |  |  |  | 5 years |
Research and development expense |  |  |  |  |  |  |  |  |  |  | $ 63.0 |  |
Additional milestone payment | $ 50.0 |  |  |  |  |  |  |  |  |  |  |  |
Due from Related Parties |  |  |  |  |  | 3.1 |  | 4.1 |  |  |  | $ 3.1 |
Due to Related Parties |  |  |  |  |  | 121.1 |  | $ 148.7 |  |  |  | $ 121.1 |
Contingent Commercialized Rights, Number Of Products | product |  |  |  | 2 |  |  |  |  |  |  |  |  |
Sangamo Therapeutics, Inc. Agreement |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Term of collaboration agreement |  |  |  |  |  |  |  |  |  |  |  | 5 years |
Other research and discovery |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Research and Development Expense (Excluding Acquired in Process Cost) |  |  |  |  |  | 18.0 |  |  |  | 77.2 |  | $ 37.5 |
InnoCare Pharma Limited (InnoCare) Agreement |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Upfront and milestone payments made to collaborative partner |  | $ 125.0 |  |  |  |  |  |  |  |  |  |  |
Contingent additional milestone payment |  | $ 812.5 |  |  |  |  |  |  |  |  |  |  |
Research and development | Eisai | ADUHELM |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Expense incurred by the collaboration |  |  |  |  |  | 37.2 |  |  |  | 42.1 |  | 81.4 | 89.1
Expense reflected within statements of income |  |  |  |  |  | 20.5 |  |  |  | 23.2 |  | 44.8 | 49.0
Research and development | Denali Therapeutics |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Expense incurred by the collaboration |  |  |  |  |  | 23.2 |  |  |  | 10.4 |  | 38.1 | 18.7
Expense reflected within statements of income |  |  |  |  |  | 13.2 |  |  |  | 6.2 |  | 22.1 | 11.2
Research and development | Samsung Bioepis |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Expense incurred by the collaboration |  |  |  |  |  | 2.6 | $ 10.2 |  |  | 5.4 |  | 10.9 |
Expense reflected within statements of income |  |  |  |  |  | 1.6 | $ 7.6 |  |  | 3.4 |  | 7.1 |
Research and development | Sage Therapeutics Inc. |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Expense incurred by the collaboration |  |  |  |  |  | 50.8 |  |  |  | 54.0 |  | 89.5 | 93.8
Expense reflected within statements of income |  |  |  |  |  | 25.3 |  |  |  | 27.0 |  | 44.7 | 46.9
Research and development | UCB Pharma S.A. [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Expense incurred by the collaboration |  |  |  |  |  | 15.6 |  |  |  | 16.1 |  | 33.2 | 33.0
Expense reflected within statements of income |  |  |  |  |  | 7.8 |  |  |  | 8.1 |  | 16.6 | 16.5
Selling, general and administrative | Eisai | BAN2401 and Elenbecestat |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Expense incurred by the collaboration |  |  |  |  |  | 23.4 |  |  |  | 4.3 |  | 39.3 | 10.0
Expense reflected within statements of income |  |  |  |  |  | 11.7 |  |  |  | 2.1 |  | 19.7 | 5.0
Selling, general and administrative | Eisai | ADUHELM |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Expense incurred by the collaboration |  |  |  |  |  | 40.8 |  |  |  | 125.6 |  | 135.8 | 237.4
Expense reflected within statements of income |  |  |  |  |  | 21.1 |  |  |  | 67.6 |  | 72.0 | 127.9
Selling, general and administrative | Sage Therapeutics Inc. |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Expense incurred by the collaboration |  |  |  |  |  | 23.0 |  |  |  | 10.5 |  | 41.4 | 15.8
Expense reflected within statements of income |  |  |  |  |  | $ 11.5 |  |  |  | $ 5.2 |  | $ 20.7 | $ 7.9

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