Allowance for Expected Credit Losses on Premiums Receivable (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023
Credit Loss [Abstract]
Premium Receivable, Allowance for Credit Loss	$ 27.6	$ 26.8	$ 27.6	$ 26.8	$ 27.0	$ 26.8	$ 30.0	$ 29.5
Premiums Receivable, Gross	691.7	659.8	691.7	659.8	$ 631.8	$ 584.1	$ 676.9	$ 612.4
Premium Receivable, Credit Loss Expense (Reversal)	$ 0.6	$ (3.2)	$ 0.8	$ (2.7)