Reinsurance - Effects Of Reinsurance (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Premiums and other considerations:
Premiums and other considerations, Direct	$ 1,563.3	$ 1,040.5
Premiums and other considerations, Ceded	(114.7)	(153.1)
Net premiums and other considerations	1,448.6	887.4
Benefits, claims and settlement expenses:
Benefits, claims and settlement expenses, Direct	2,107.8	1,629.5
Benefits, claims and settlement expenses, Ceded	(333.9)	(138.8)
Net benefits, claims and settlement expenses	1,773.9	1,490.7
Liability for future policy benefits remeasurement (gain) loss:
Liability for future policy benefits remeasurement (gain) loss, Direct	12.7	20.3
Liability for future policy benefits remeasurement (gain) loss, Ceded	(18.3)	(6.9)
Net liability for future policy benefits remeasurement (gain) loss	$ (5.6)	$ 13.4