Unpaid Loss and Loss Adjustment Expense - Claims Development Information, Incurred Losses (Details) $ in Millions	Dec. 31, 2023 USD ($)	Dec. 31, 2023 segment	Dec. 31, 2023 claim	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Home and renters
Claims Development [Line Items]
Total incurred losses and ALAE, net	$ 407.8
IBNR	26.3
Cumulative Number of Reported Claims | claim			228,226
Pet
Claims Development [Line Items]
Total incurred losses and ALAE, net	87.3
IBNR	5.2
Cumulative Number of Reported Claims | segment		1,082,139,000,000
Car
Claims Development [Line Items]
Total incurred losses and ALAE, net	355.3
IBNR	40.3
Cumulative Number of Reported Claims | segment		289,930
2016 | Home and renters
Claims Development [Line Items]
Total incurred losses and ALAE, net	0.0			$ 0.0	$ 0.0	$ 0.0	$ 0.0	$ 0.0	$ 0.0	$ 0.0
IBNR	0.0
Cumulative Number of Reported Claims | segment		8
2016 | Car
Claims Development [Line Items]
Total incurred losses and ALAE, net	2.3			2.0	1.8	1.7	1.7	1.7	2.0	$ 1.6
IBNR	0.0
Cumulative Number of Reported Claims | segment		1,640
2017 | Home and renters
Claims Development [Line Items]
Total incurred losses and ALAE, net	1.7			1.7	1.7	1.7	1.7	1.7	1.7
IBNR	0.0
Cumulative Number of Reported Claims | claim			1,756
2017 | Car
Claims Development [Line Items]
Total incurred losses and ALAE, net	24.4			32.5	32.3	31.4	30.2	30.0	$ 28.6
IBNR	(0.1)
Cumulative Number of Reported Claims | segment		29,057
2018 | Home and renters
Claims Development [Line Items]
Total incurred losses and ALAE, net	13.4			13.4	13.4	13.4	13.5	15.0
IBNR	0.0
Cumulative Number of Reported Claims | claim			10,527
2018 | Car
Claims Development [Line Items]
Total incurred losses and ALAE, net	26.2			33.9	31.8	31.9	29.7	$ 31.4
IBNR	0.7
Cumulative Number of Reported Claims | segment		44,102
2019 | Home and renters
Claims Development [Line Items]
Total incurred losses and ALAE, net	46.1			46.3	46.3	46.1	46.0
IBNR	0.0
Cumulative Number of Reported Claims | claim			19,498
2019 | Car
Claims Development [Line Items]
Total incurred losses and ALAE, net	25.4			24.6	23.2	24.9	$ 24.2
IBNR	2.3
Cumulative Number of Reported Claims | segment		51,132
2020 | Home and renters
Claims Development [Line Items]
Total incurred losses and ALAE, net	52.4			51.5	51.5	53.0
IBNR	0.1
Cumulative Number of Reported Claims		20,873,000,000	30,336
2020 | Pet
Claims Development [Line Items]
Total incurred losses and ALAE, net	0.6			1.0	0.6	0.7
IBNR	0.0
2020 | Car
Claims Development [Line Items]
Total incurred losses and ALAE, net	19.1			11.8	12.0	$ 10.8
IBNR	3.0
Cumulative Number of Reported Claims | segment		37,320
2021 | Home and renters
Claims Development [Line Items]
Total incurred losses and ALAE, net	58.4			55.9	59.4
IBNR	0.6
Cumulative Number of Reported Claims		196,773,000,000	53,442
2021 | Pet
Claims Development [Line Items]
Total incurred losses and ALAE, net	9.5			9.7	10.0
IBNR	0.0
2021 | Car
Claims Development [Line Items]
Total incurred losses and ALAE, net	86.8			75.3	$ 75.3
IBNR	6.3
Cumulative Number of Reported Claims | segment		43,091
2022 | Home and renters
Claims Development [Line Items]
Total incurred losses and ALAE, net	92.6			96.5
IBNR	3.5
Cumulative Number of Reported Claims		375,550,000,000	55,758
2022 | Pet
Claims Development [Line Items]
Total incurred losses and ALAE, net	25.3			27.4
IBNR	0.1
2022 | Car
Claims Development [Line Items]
Total incurred losses and ALAE, net	92.0			$ 83.1
IBNR	11.2
Cumulative Number of Reported Claims | segment		46,623
2023
Claims Development [Line Items]
Total incurred losses and ALAE, net	51.9
2023 | Home and renters
Claims Development [Line Items]
Total incurred losses and ALAE, net	143.2
IBNR	22.1
Cumulative Number of Reported Claims		488,943,000,000	56,901
2023 | Pet
Claims Development [Line Items]
IBNR	5.1
2023 | Car
Claims Development [Line Items]
Total incurred losses and ALAE, net	79.1
IBNR	$ 16.9
Cumulative Number of Reported Claims | segment		36,965