Short-Duration Insurance Contracts - Schedule of Reinsurance Reserve Balances (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 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	16.3	$ 17.4
Claims and claim expense payments for claims occurring during:
Ending gross reserves	577.1
Property & Casualty
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning gross reserves	420.6	416.8
Less: reinsurance recoverables	100.8	104.0
Net reserves, beginning of period	319.8	312.8
Incurred claims and claim expenses:
Claims occurring in the current period	123.7	124.7
Increase (decrease) in estimated reserves for claims occurring in prior periods	(5.3)	0.0
Total claims and claim expenses incurred	118.4	124.7
Claims and claim expense payments for claims occurring during:
Current period	50.0	44.6
Prior periods	69.8	78.3
Total claims and claim expense payments	119.8	122.9
Net reserves, end of period	318.4	314.6
Plus: reinsurance recoverables	98.3	103.6
Ending gross reserves	416.7	418.2
Group Benefits
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning gross reserves	104.9	116.6
Less: reinsurance recoverables	25.2	27.7
Net reserves, beginning of period	79.7	88.9
Incurred claims and claim expenses:
Claims occurring in the current period	18.3	20.2
Increase (decrease) in estimated reserves for claims occurring in prior periods	0.4	(6.1)
Total claims and claim expenses incurred	18.7	14.1
Claims and claim expense payments for claims occurring during:
Current period	3.8	3.9
Prior periods	11.6	12.4
Total claims and claim expense payments	15.4	16.3
Net reserves, end of period	83.1	86.7
Plus: reinsurance recoverables	25.9	27.6
Ending gross reserves	$ 109.0	$ 114.3