Allowance for Expected Credit Losses on Premiums Receivable (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Jan. 01, 2020
Credit Loss [Abstract]
Premium Receivable, Allowance for Credit Loss	$ 32.6	$ 41.1	$ 32.6	$ 41.1	$ 31.0	$ 38.8	$ 47.5	$ 23.8
Premiums Receivable, Gross	575.8	597.3	575.8	597.3	$ 576.3	$ 525.8	$ 627.0	$ 543.0
Premium Receivable, Credit Loss Expense (Reversal)	1.6	$ (6.4)	(6.2)	17.3
Impairment Loss on ROU Asset	$ 0.0		$ 13.9	$ 12.7