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Note 5 - Investments - Investment Gains (Losses), Net (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Gain (Loss) on Investments | $ 70.8 | $ 43.4 | $ (113.3)
Seeded Investment Products and Hedges, Net [Member] |  |  |
Gain (Loss) on Investments | 36.4 | 20.3 | (15.2)
Third-party Ownership Interests in Seeded Investment Products [Member] |  |  |
Gain (Loss) on Investments | 37.5 | 34.7 | (97.9)
Equity Method Investments [Member] |  |  |
Gain (Loss) on Investments | (5.6) | (13.5) | 2.9
Other Security Investments [Member] |  |  |
Gain (Loss) on Investments | $ 2.5 | $ 1.9 | $ (3.1)

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- Definition Amount of realized and unrealized gain (loss) on investment. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(9)(a)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(7)(c)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2 Reference 3: http://www.xbrl.org/2003/role/recommendedDisclosureRef -Topic 230 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 28 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482740/230-10-45-28 + Details
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