CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Millions	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2021		61,660,996
Beginning balance at Dec. 31, 2021	$ 988.2	$ 0.0	$ 1,553.5	$ (561.9)	$ (3.4)
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Issuance of common stock from acquisition of Metromile (Note 5) (in shares)		6,901,934
Issuance of common stock from acquisition of Metromile (Note 5)	137.7		137.7
Exercise of stock options and distribution of restricted stock units (in shares)		712,100
Exercise of stock options and distribution of restricted stock units	3.6		3.6
Stock-based compensation	59.3		59.3
Net loss	(297.8)			(297.8)
Other comprehensive income (loss)	(24.2)				(24.2)
Ending balance (in shares) at Dec. 31, 2022		69,275,030
Ending balance at Dec. 31, 2022	866.8	$ 0.0	1,754.1	(859.7)	(27.6)
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Exercise of stock options and distribution of restricted stock units (in shares)		888,673
Exercise of stock options and distribution of restricted stock units	0.5		0.5
Stock-based compensation	59.9		59.9
Net loss	(236.9)			(236.9)
Other comprehensive income (loss)	$ 18.6				18.6
Ending balance (in shares) at Dec. 31, 2023	70,163,703	70,163,703
Ending balance at Dec. 31, 2023	$ 708.9	$ 0.0	1,814.5	(1,096.6)	(9.0)
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Exercise of stock options and distribution of restricted stock units (in shares)	945,062	2,376,082
Exercise of stock options and distribution of restricted stock units	$ 19.3		19.3
Exercise of warrant shares (in shares)		181,081
Stock-based compensation	64.5		64.5
Net loss	(202.2)			(202.2)
Other comprehensive income (loss)	$ 2.9				2.9
Ending balance (in shares) at Dec. 31, 2024	72,720,866	72,720,866
Ending balance at Dec. 31, 2024	$ 593.4	$ 0.0	$ 1,898.3	$ (1,298.8)	$ (6.1)