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Note 6 - Derivative Instruments - Derivative Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Futures [Member]
Notional value of derivative	$ 789.0	$ 1,018.0
Futures [Member] | Seeded Investment Products [Member]
Notional value of derivative	160.5	1,555.1
Foreign Currency, Forward Contracts and Swaps [Member]
Notional value of derivative	328.2	176.2
Foreign Currency, Forward Contracts and Swaps [Member] | Not Designated as Hedging Instrument, Economic Hedge [Member]
Notional value of derivative	38.4	65.3
Foreign Currency, Forward Contracts and Swaps [Member] | Seeded Investment Products [Member]
Notional value of derivative	196.6	135.3
Credit Default Swaps [Member]
Notional value of derivative	148.5	199.7
Credit Default Swaps [Member] | Seeded Investment Products [Member]
Notional value of derivative	4.3	13.2
Total Return Swaps [Member]
Notional value of derivative	69.7	51.8
Total Return Swaps [Member] | Seeded Investment Products [Member]
Notional value of derivative	10.3	0.3
Interest Rate Swap [Member] | Seeded Investment Products [Member]
Notional value of derivative	13.9	2.2
Other [Member] | Seeded Investment Products [Member]
Notional value of derivative	$ 0.0	$ 0.3

X

- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1B

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1A

+ Details

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X

- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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