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Note 5 - Investments - Investment Gains (Losses), Net (Details) - USD ($) $ in Millions	12 Months Ended
	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)

X

- 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

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