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Investments - Debt Securities, Available-for-Sale (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Available-for-Sale
Cost	$ 0.0	$ 405.4
Unrealized gains	0.0	0.0
Unrealized losses	0.0	(0.1)
Fair value	0.0	405.3
Trading
Cost	24.6	17.9
Unrealized gains	0.0	0.0
Unrealized losses	(0.3)	(0.1)
Fair value	$ 24.3	$ 17.8

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Debt Securities, Trading, Accumulated Gross Unrealized Gain Before Tax

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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