Future Policy Benefits and Claims - Liability for Unpaid Claims (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Change in unpaid claims
Balance at beginning of period, unpaid claims	$ 1,395.0	$ 1,370.9
Balance at beginning of period, reinsurance recoverables for unpaid claims	68.6	68.7
Net balance at beginning of period	1,326.4	1,302.2
Incurred:
Incurred: Current year	429.4	404.6
Incurred: Prior years	(40.8)	(15.0)
Total incurred	388.6	389.6
Payments:
Payments: Current year	225.9	205.3
Payments: Prior years	162.5	174.1
Total payments	388.4	379.4
Net balance at end of period	1,326.6	1,312.4
Balance at end of period, reinsurance recoverables for unpaid claims	69.6	68.9
Balance at end of period, unpaid claims	$ 1,396.2	$ 1,381.3