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Fair Value (Available-For-Sale Securities) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2024	Jun. 30, 2025	Dec. 31, 2024
Fair Value Disclosure [Line Items]
Amortized Cost			$ 147.9	$ 91.9
Gross Unrealized Gains			1.4	0.5
Gross Unrealized Losses			(4.3)	(5.6)
Allowance for Credit Loss			(0.1)	(0.1)
Fair Value			144.9	86.7
Debt Securities, Available-for-Sale, Realized Gain	$ 0.1	$ 0.5
U.S. Treasury debt securities
Fair Value Disclosure [Line Items]
Amortized Cost			4.3
Gross Unrealized Gains			0.0
Gross Unrealized Losses			0.0
Allowance for Credit Loss			0.0
Fair Value			4.3
Corporate/Other debt securities
Fair Value Disclosure [Line Items]
Amortized Cost			143.6	91.9
Gross Unrealized Gains			1.4	0.5
Gross Unrealized Losses			(4.3)	(5.6)
Allowance for Credit Loss			(0.1)	(0.1)
Fair Value			140.6	86.7
Debt Securities, Available-for-sale, Unrealized Loss Position			61.6	$ 70.1
US Treasury Securities
Fair Value Disclosure [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position			$ 2.7