Unpaid Claims and Claim Expense Reserves - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Automobile liability coverage percent reserves	71.40%
Short tail coverage reserves as a percentage of total reserves	28.30%
Long tail coverage reserves as percentage of reserves	71.40%
Percentage of losses incurred	99.70%
Potential variability of property and casualty loss reserves	2.00%
Probability of other possible outcomes possible impact on net income	$ 2.0
Sensitivity analysis, hypothetical change in loss ratio, percent	1.00%
Sensitivity analysis, hypothetical change in loss ratio, amount	$ 0.8
Property & Casualty
Segment Reporting Information [Line Items]
Favorable (unfavorable) development of total reserves for claims occurring in prior years, net	(22.0)	$ 7.2	$ 10.2
Unfavorable development of total reserves for claims occurring in prior years	28.0
Favorable development of total reserves for claims occurring in prior years	6.0
Group benefits
Segment Reporting Information [Line Items]
Favorable (unfavorable) development of total reserves for claims occurring in prior years, net	$ 11.1
2018 Camp Fire In California
Segment Reporting Information [Line Items]
Favorable (unfavorable) development of total reserves for claims occurring in prior years, net			$ 4.8