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Collaborative and Other Relationships - Equity Method Investments (Details) ₩ in Millions, $ in Millions | 1 Months Ended | 3 Months Ended | 9 Months Ended |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Apr. 30, 2022 USD ($) | Dec. 31, 2019 | Sep. 30, 2022 USD ($) | Mar. 31, 2022 USD ($) | Dec. 31, 2021 USD ($) | Sep. 30, 2021 USD ($) | Mar. 31, 2020 USD ($) | Sep. 30, 2022 USD ($) | Sep. 30, 2021 USD ($) | Sep. 30, 2022 KRW (₩) | Jun. 30, 2022 KRW (₩) | Jan. 31, 2022 USD ($) | Dec. 31, 2021 KRW (₩) | Jan. 31, 2020 USD ($) | Nov. 07, 2018 USD ($)
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income (loss) from equity method investments |  |  |  |  |  |  |  | $ 2.6 | $ 17.2 |  |  |  |  |  |
Collaboration profit (loss) sharing |  |  | $ 45.3 |  |  | $ 21.2 |  | (42.6) | 74.5 |  |  |  |  |  |
ADUHELM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Research and development expense |  |  |  |  |  |  |  | $ 300.0 |  |  |  |  |  |  |
Samsung Bioepis |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of stake in entity maximum |  |  | 49.90% |  |  |  |  | 49.90% |  | 49.90% |  |  |  |  |
Amortization of basis differences |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 675.0
Loss recorded on Samsung Bioepis joint venture |  |  |  |  |  | 1.1 |  | $ 2.6 | 17.2 |  |  |  |  |  |
Income (loss) from equity method investments |  |  |  |  |  | 8.9 |  | 17.0 | 39.5 |  |  |  |  |  |
Investment in Samsung Bioepis |  |  |  |  | $ 599.9 |  |  |  |  | ₩ 0.0 |  |  | ₩ 713,300.0 |  |
Collaboration profit (loss) sharing |  |  | $ 48.7 |  |  | 71.8 |  | 171.4 | 210.2 |  |  |  |  |  |
Eisai |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income (loss) from equity method investments |  |  | 3.4 |  |  | 50.6 |  | 214.0 | $ 90.7 |  |  |  |  |  |
Due to Related Parties |  |  | 81.7 |  | 46.5 |  |  | 81.7 |  |  |  |  |  |  |
Eisai | ADUHELM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income (loss) from equity method investments |  |  |  | $ 59.0 | 45.0 | $ 45.0 |  | $ 177.0 |  |  |  |  |  |  |
Samsung Bioepis |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from divestiture of interest in joint venture | $ 1,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment in Samsung Bioepis | ₩ |  |  |  |  |  |  |  |  |  |  | ₩ 581.6 |  |  |  |
Payables to divestiture of interest in joint venture |  |  |  |  |  |  |  |  |  |  |  | $ 1,300.0 |  |  |
Equity Method Investments, Expected Profit Share |  | 45.00% |  |  |  |  |  | 50.00% |  |  |  |  |  |  |
Upfront and milestone payments made to collaborative partner |  |  |  |  |  |  | $ 100.0 |  |  |  |  |  |  |  |
Research and development expense |  |  |  |  |  |  | $ 63.0 |  |  |  |  |  |  |  |
Prepaid research and development expenses |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 37.0 |
Accrued milestone payments |  |  | 15.0 |  |  |  |  |  |  |  |  |  |  |  |
Estimated additional payments upon achievement of development and commercial milestones |  |  |  |  |  |  |  | $ 180.0 |  |  |  |  |  |  |
Contract Option Exercise Fee |  |  |  |  |  |  |  | 60.0 |  |  |  |  |  |  |
Due to Related Parties |  |  | $ 53.8 |  | $ 148.7 |  |  | $ 53.8 |  |  |  |  |  |  |
Samsung Bioepis | Payment Due At First Anniversary |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payables to divestiture of interest in joint venture |  |  |  |  |  |  |  |  |  |  |  | 812.5 |  |  |
Samsung Bioepis | Payment Due At Second Anniversary |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payables to divestiture of interest in joint venture |  |  |  |  |  |  |  |  |  |  |  | $ 437.5 |  |  |
Inventory | Samsung Bioepis |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity method investment basis difference amortization period |  |  |  |  |  |  |  | 1 year 6 months |  |  |  |  |  |  |
Developed technology | Samsung Bioepis |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity method investment basis difference amortization period |  |  |  |  |  |  |  | 15 years |  |  |  |  |  |  |

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