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Financial Instruments - Marketable debt and equity securities (Details) - USD ($) $ in Millions | Jun. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Net Investment Income [Line Items] |  |
Amortized Cost | $ 668.7 | $ 668.7
Gross Unrealized Gains | 0.0 | 0.0
Gross Unrealized Losses | (511.7) | (489.0)
Fair Value | 157.0 | 179.7
Equity Securities, Non-Current |  |
Net Investment Income [Line Items] |  |
Amortized Cost | 668.7 | 668.7
Gross Unrealized Gains | 0.0 | 0.0
Gross Unrealized Losses | (511.7) | (489.0)
Fair Value | $ 157.0 | $ 179.7

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