Allowance for Expected Credit Losses on Premiums Receivable (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021	Dec. 31, 2020
Credit Loss [Abstract]
Premium Receivable, Allowance for Credit Loss	$ 31.4	$ 32.6	$ 31.4	$ 32.6	$ 34.3	$ 34.2	$ 31.0	$ 38.8
Premiums Receivable, Gross	561.1	575.8	561.1	575.8	$ 593.4	$ 530.7	$ 576.3	$ 525.8
Premium Receivable, Credit Loss Expense (Reversal)	$ (2.9)	$ 1.6	$ (2.8)	$ (6.2)