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Fair Value (Available-For-Sale Securities) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Fair Value Disclosure [Line Items]
Amortized Cost		$ 160.4		$ 91.9
Gross Unrealized Gains		2.3		0.5
Gross Unrealized Losses		(3.6)		(5.6)
Allowance for Credit Loss		(0.1)		(0.1)
Fair Value		159.0		86.7
Debt Securities, Available-for-Sale, Realized Gain	$ 0.1	0.1	$ 0.5
U.S. Treasury debt securities
Fair Value Disclosure [Line Items]
Amortized Cost		10.6
Gross Unrealized Gains		0.0
Gross Unrealized Losses		0.0
Allowance for Credit Loss		0.0
Fair Value		10.6
Corporate/Other debt securities
Fair Value Disclosure [Line Items]
Amortized Cost		149.8		91.9
Gross Unrealized Gains		2.3		0.5
Gross Unrealized Losses		(3.6)		(5.6)
Allowance for Credit Loss		(0.1)		(0.1)
Fair Value		148.4		86.7
Debt Securities, Available-for-sale, Unrealized Loss Position		55.9		$ 70.1
US Treasury Securities
Fair Value Disclosure [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position		$ 1.5