Allowance for Expected Credit Losses on Premiums Receivable (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2021
Credit Loss [Abstract]
Premium Receivable, Allowance for Credit Loss	$ 28.7	$ 34.3	$ 28.7	$ 31.6	$ 32.5	$ 35.0	$ 34.2
Premiums Receivable, Gross	660.3	593.4	660.3	$ 635.6	$ 557.6	$ 600.9	$ 530.7
Premium Receivable, Credit Loss Expense (Reversal)	$ (2.9)	$ (0.7)	$ (3.8)