Allowance for Expected Credit Losses on Premiums Receivable (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Jan. 01, 2020
Credit Loss [Abstract]
Premium Receivable, Allowance for Credit Loss	$ 31.0	$ 47.5	$ 31.0	$ 47.5	$ 33.7	$ 38.8	$ 32.6	$ 23.8
Premiums Receivable, Gross	576.3	627.0	576.3	627.0	$ 602.9	$ 525.8	$ 607.2	$ 543.0
Premium Receivable, Credit Loss Expense (Reversal)	2.7	$ 14.9	$ 7.8	23.7
Impairment Loss on ROU Asset	$ 13.9			$ 12.7