Allowance for Expected Credit Losses on Premiums Receivable (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2021	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Credit Loss [Abstract]
Premium Receivable, Allowance for Credit Loss	$ 34.3	$ 31.0	$ 31.0	$ 35.0	$ 34.2	$ 33.7	$ 38.8
Premiums Receivable, Gross	593.4	576.3	576.3	$ 600.9	$ 530.7	$ 602.9	$ 525.8
Premium Receivable, Credit Loss Expense (Reversal)	$ (0.7)	$ (2.7)	$ (7.8)