Unpaid Claims and Claim Expenses - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Automobile liability coverage percent reserves	74.00%
Short tail coverage reserves as a percentage of total reserves	26.00%
Long tail coverage reserves as percentage of reserves	74.00%
Percentage of losses incurred	99.00%
Potential variability of property and casualty loss reserves	6.00%
Probability of other possible outcomes possible impact on net income	$ 12.0
Favorable development of total reserves for property and casualty claims occurring in prior years	10.2	$ 7.5	$ 0.3
2018 Camp Fire In California
Segment Reporting Information [Line Items]
Favorable development of total reserves for property and casualty claims occurring in prior years	$ 4.8