Reinsurance - Effects Of Reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Premiums and other considerations:
Premiums and other considerations, Direct	$ 5,796.1	$ 5,492.1	$ 6,647.1
Premiums and other considerations, Ceded	(456.4)	(650.6)	(609.7)
Net premiums and other considerations	5,339.7	4,841.5	6,037.4
Benefits, claims and settlement expenses:
Benefits, claims and settlement expenses, Direct	7,947.0	7,766.2	8,810.1
Benefits, claims and settlement expenses, Ceded	(1,576.2)	(669.2)	(528.6)
Net benefits, claims and settlement expenses	$ 6,370.8	$ 7,097.0	$ 8,281.5