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Note 4 - Investments - Investment Gains (Losses), Net (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2025 | Jun. 30, 2024 | Jun. 30, 2025 | Jun. 30, 2024
Investment gains, net | $ 52.6 | $ 6.4 | $ 47.1 | $ 28.9
Seeded Investment Products and Hedges, Net [Member] |  |  |  |
Investment gains, net | 13.8 | 4.6 | 19.6 | 16.5
Third-party Ownership Interests in Seeded Investment Products [Member] |  |  |  |
Investment gains, net | 36.7 | 3.8 | 33.4 | 14.3
Equity Method Investments [Member] |  |  |  |
Investment gains, net | (1.6) | (2.1) | (3.3) | (3.5)
Other Security Investments [Member] |  |  |  |
Investment gains, net | $ 3.7 | $ 0.1 | $ (2.6) | $ 1.6

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