Short-Duration Insurance Contracts - Schedule of Reinsurance Reserve Balances (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning gross reserves			$ 569.2
Incurred claims and claim expenses:
Total claims and claim expenses incurred	$ 18.1	$ 17.7	51.6	$ 53.2
Claims and claim expense payments for claims occurring during:
Ending gross reserves	564.1		564.1
Property & Casualty
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning gross reserves	419.8	432.9	420.6	416.8
Less: reinsurance recoverables	98.8	101.7	100.8	104.0
Net reserves, beginning of period	321.0	331.2	319.8	312.8
Incurred claims and claim expenses:
Claims occurring in the current period	126.3	147.8	391.9	431.4
Increase (decrease) in estimated reserves for claims occurring in prior periods	(3.0)	(13.0)	(13.8)	(19.2)
Total claims and claim expenses incurred	123.3	134.8	378.1	412.2
Claims and claim expense payments for claims occurring during:
Current period	99.5	102.3	239.2	241.0
Prior periods	39.2	31.6	153.1	152.0
Total claims and claim expense payments	138.7	133.9	392.3	393.0
Net reserves, end of period	305.6	332.1	305.6	332.1
Plus: reinsurance recoverables	98.7	101.3	98.7	101.3
Ending gross reserves	404.3	433.4	404.3	433.4
Group Benefits
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning gross reserves	113.2	116.1	104.9	116.6
Less: reinsurance recoverables	25.8	28.0	25.2	27.7
Net reserves, beginning of period	87.4	88.1	79.7	88.9
Incurred claims and claim expenses:
Claims occurring in the current period	15.6	18.5	52.6	58.0
Increase (decrease) in estimated reserves for claims occurring in prior periods	(2.6)	(3.9)	(5.2)	(13.2)
Total claims and claim expenses incurred	13.0	14.6	47.3	44.8
Claims and claim expense payments for claims occurring during:
Current period	9.9	10.5	19.6	22.6
Prior periods	5.6	4.8	22.5	23.7
Total claims and claim expense payments	15.4	15.3	42.1	46.3
Net reserves, end of period	85.0	87.4	85.0	87.4
Plus: reinsurance recoverables	26.0	27.8	26.0	27.8
Ending gross reserves	$ 111.0	$ 115.2	$ 111.0	$ 115.2