Short-Duration Insurance Contracts - Schedule of Reinsurance Reserve Balances (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning gross reserves	$ 565.2
Claims and claim expense payments for claims occurring during:
Ending gross reserves	573.8
Property & Casualty
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning gross reserves	404.5	$ 420.6
Less: reinsurance recoverables	101.2	100.8
Net reserves, beginning of period	303.3	319.8
Incurred claims and claim expenses:
Claims occurring in the current period	119.2	123.7
Increase (decrease) in estimated reserves for claims occurring in prior periods	(5.0)	(5.3)
Total claims and claim expenses incurred	114.2	118.4
Claims and claim expense payments for claims occurring during:
Current period	44.8	50.0
Prior periods	67.3	69.8
Total claims and claim expense payments	112.1	119.8
Net reserves, end of period	305.4	318.4
Plus: reinsurance recoverables	101.5	98.3
Ending gross reserves	406.9	416.7
Group Benefits
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning gross reserves	113.2	104.9
Less: reinsurance recoverables	26.5	25.2
Net reserves, beginning of period	86.7	79.7
Incurred claims and claim expenses:
Claims occurring in the current period	21.8	18.3
Increase (decrease) in estimated reserves for claims occurring in prior periods	(2.7)	0.4
Total claims and claim expenses incurred	19.1	18.7
Claims and claim expense payments for claims occurring during:
Current period	4.7	3.8
Prior periods	11.3	11.6
Total claims and claim expense payments	16.0	15.4
Net reserves, end of period	89.7	83.1
Plus: reinsurance recoverables	27.0	25.9
Ending gross reserves	$ 116.7	$ 109.0