Segment Information - Schedule of Segment Reporting Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Jul. 28, 2022
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	$ 526.5	$ 429.8	$ 256.7
less: Loss and loss adjustment expenses, net	277.0	280.4	167.3
Other insurance expense	76.8	59.2	44.0
Sales and marketing	166.3	101.9	138.3
Advertising expenses	121.5	55.2	88.5
Technology development	85.8	88.8	79.6
General and administrative	124.5	129.3	122.3
Income tax (benefit) expense	(1.7)	7.1	3.0
Net loss	(202.2)	(236.9)	(297.8)
Impairment loss on subleased right-of-use asset		3.7
Metromile
Revenues from External Customers and Long-Lived Assets [Line Items]
Liabilities assumed		3.0		$ 134.5
Business acquisition, transaction costs			8.4
Reportable Segment
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	526.5	429.8	256.7
less: Loss and loss adjustment expenses, net	277.0	280.4	167.3
Other insurance expense	76.8	59.2	44.0
Sales and marketing	44.8	46.7	49.8
Advertising expenses	121.5	55.2	88.5
Technology development	85.8	88.8	79.6
General and administrative	98.0	102.2	101.7
Interest expense	6.2	0.4	0.0
Depreciation and amortization	20.0	20.0	12.2
Other expenses	0.3	6.7	8.4
Income tax (benefit) expense	(1.7)	7.1	3.0
Net loss	(202.2)	$ (236.9)	$ (297.8)
New York
Revenues from External Customers and Long-Lived Assets [Line Items]
Impairment loss on subleased right-of-use asset	$ 0.3