Liability for Future Policyholder Benefits - Changes in Deferred Profit Liability (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024
Deferred Profit Liability [Roll Forward]
Balance, beginning of period	$ 412.1	$ 337.8
Profits deferred	79.6	81.4
Interest accrual	9.7	8.1
Amortization	(57.6)	(53.9)
Effect of actual variances from expected experience and other changes	0.7	0.7
Balance, end of period	$ 444.5	$ 374.1