Unpaid Claims and Claim Expenses - Summary of Reinsurance Reserve Balances (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Segment Reporting Information
Beginning gross reserves	$ 425.9
Claims and claim expense payments for claims occurring during:
Ending gross reserves	475.7
Benefits, claims and settlement expenses	177.0	$ 134.3
Property & Casualty
Segment Reporting Information
Beginning gross reserves	362.4	372.2
Less: reinsurance recoverables	110.3	112.9
Net reserves, beginning of period	252.1	259.3
Incurred claims and claim expenses:
Claims occurring in the current period	108.3	94.8
Decrease in estimated reserves for claims occurring in prior periods	0.0	0.0
Total claims and claim expenses incurred	108.3	94.8
Claims and claim expense payments for claims occurring during:
Current period	33.8	34.4
Prior periods	78.4	58.1
Total claims and claim expense payments	112.2	92.5
Net reserves, end of period	248.2	261.6
Plus: reinsurance recoverables	108.0	112.5
Ending gross reserves	356.2	374.1
Life and Annuity Segments
Claims and claim expense payments for claims occurring during:
Net reserves, end of period	119.5	78.4
Benefits, claims and settlement expenses	$ 68.7	$ 39.5