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Note 6 - Derivative Instruments - Change in Fair Value of Derivatives (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Gain (losses) from derivative instruments	$ (16.4)	$ (17.9)	$ 56.2
Futures [Member]
Gain (losses) from derivative instruments	(10.5)	(7.0)	40.8
Credit Default Swaps [Member]
Gain (losses) from derivative instruments	(3.0)	(6.5)	3.7
Total Return Swaps [Member]
Gain (losses) from derivative instruments	(9.3)	(12.8)	21.3
Foreign Currency, Forward Contracts and Swaps [Member]
Gain (losses) from derivative instruments	$ 6.4	$ 8.4	$ (9.6)

X

- Definition

Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4A

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Details

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Namespace Prefix:
Data Type:	na
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- Details

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X

- Details

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- Details

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- Details

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