Reinsurance - Effects Of Reinsurance (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Premiums and other considerations:
Premiums and other considerations, Direct	$ 1,591.7	$ 1,395.7	$ 4,068.9	$ 3,803.2
Premiums and other considerations, Ceded	(105.2)	(165.2)	(328.8)	(467.9)
Net premiums and other considerations	1,486.5	1,230.5	3,740.1	3,335.3
Benefits, claims and settlement expenses:
Benefits, claims and settlement expenses, Direct	2,117.0	1,924.5	5,639.9	5,418.4
Benefits, claims and settlement expenses, Ceded	(382.2)	(153.6)	(1,166.6)	(460.0)
Net benefits, claims and settlement expenses	$ 1,734.8	$ 1,770.9	$ 4,473.3	$ 4,958.4