Short-Duration Insurance Contracts - Schedule of Reinsurance Reserve Balances (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross reserves, beginning of year	$ 581.7
Less: reinsurance recoverables	424.2
Incurred claims and claim expenses:
Total claims and claim expenses incurred	72.8	$ 71.5	$ 66.3
Claims and claim expense payments for claims occurring during:
Plus: reinsurance recoverables	404.3	424.2
Gross reserves, end of year	569.2	581.7
Group benefits
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Less: reinsurance recoverables	306.2
Claims and claim expense payments for claims occurring during:
Plus: reinsurance recoverables	289.3	306.2
Property & Casualty
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross reserves, beginning of year	416.8	388.7	362.4
Less: reinsurance recoverables	104.0	100.8	110.3
Net reserves, beginning of year	312.8	287.9	252.1
Incurred claims and claim expenses:
Claims occurring in the current year	552.8	557.0	512.3
Increase (decrease) in estimated reserves for claims occurring in prior years	(11.8)	0.0	22.0
Total claims and claim expenses incurred	541.0	557.0	534.3
Claims and claim expense payments for claims occurring during:
Current year	368.1	353.1	320.0
Prior years	165.9	179.0	178.5
Total claims and claim expense payments	534.0	532.1	498.5
Net reserves, end of year	319.8	312.8	287.9
Plus: reinsurance recoverables	100.8	104.0	100.8
Gross reserves, end of year	420.6	416.8	388.7
Group benefits
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross reserves, beginning of year	116.6	121.6
Less: reinsurance recoverables	27.7	27.9
Net reserves, beginning of year	88.9	93.7
Incurred claims and claim expenses:
Claims occurring in the current year	66.3	73.6
Increase (decrease) in estimated reserves for claims occurring in prior years	(14.5)	(13.9)
Total claims and claim expenses incurred	51.8	59.7
Claims and claim expense payments for claims occurring during:
Current year	31.1	33.8
Prior years	29.9	30.7
Total claims and claim expense payments	61.0	64.5
Net reserves, end of year	79.7	88.9	93.7
Plus: reinsurance recoverables	25.2	27.7	27.9
Gross reserves, end of year	$ 104.9	$ 116.6	$ 121.6