CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS’ EQUITY - USD ($) $ in Millions	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive (Loss) Income
Beginning balance (in shares) at Dec. 31, 2020		56,774,294
Beginning balance at Dec. 31, 2020	$ 541.0	$ 0.0	$ 859.8	$ (320.6)	$ 1.8
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Exercise of stock options and distribution of restricted stock units(in shares)		577,162
Exercise of stock options and distribution of restricted stock units	6.1		6.1
Issuance of common stock (in shares)		4,018,647
Issuance of common stock	640.3		640.3
Stock-based compensation	6.1		6.1
Net loss	(49.0)			(49.0)
Other comprehensive income (loss)	(0.8)				(0.8)
Ending balance (in shares) at Mar. 31, 2021		61,370,103
Ending balance at Mar. 31, 2021	1,143.7	$ 0.0	1,512.3	(369.6)	1.0
Beginning balance (in shares) at Dec. 31, 2020		56,774,294
Beginning balance at Dec. 31, 2020	541.0	$ 0.0	859.8	(320.6)	1.8
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Net loss	(171.0)
Ending balance (in shares) at Sep. 30, 2021		61,615,624
Ending balance at Sep. 30, 2021	1,048.0	$ 0.0	1,539.5	(491.6)	0.1
Beginning balance (in shares) at Mar. 31, 2021		61,370,103
Beginning balance at Mar. 31, 2021	1,143.7	$ 0.0	1,512.3	(369.6)	1.0
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Exercise of stock options and distribution of restricted stock units(in shares)		162,024
Exercise of stock options and distribution of restricted stock units	1.7		1.7
Stock-based compensation	11.9		11.9
Net loss	(55.6)			(55.6)
Other comprehensive income (loss)	(0.1)				(0.1)
Ending balance (in shares) at Jun. 30, 2021		61,532,127
Ending balance at Jun. 30, 2021	1,101.6	$ 0.0	1,525.9	(425.2)	0.9
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Exercise of stock options and distribution of restricted stock units(in shares)		83,497
Exercise of stock options and distribution of restricted stock units	0.9		0.9
Stock-based compensation	12.7		12.7
Net loss	(66.4)			(66.4)
Other comprehensive income (loss)	(0.8)				(0.8)
Ending balance (in shares) at Sep. 30, 2021		61,615,624
Ending balance at Sep. 30, 2021	$ 1,048.0	$ 0.0	1,539.5	(491.6)	0.1
Beginning balance (in shares) at Dec. 31, 2021	61,660,996	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]
Exercise of stock options and distribution of restricted stock units(in shares)		97,743
Exercise of stock options and distribution of restricted stock units	0.6		0.6
Stock-based compensation	14.1		14.1
Net loss	(74.8)			(74.8)
Other comprehensive income (loss)	(15.4)				(15.4)
Ending balance (in shares) at Mar. 31, 2022		61,758,739
Ending balance at Mar. 31, 2022	$ 912.7	$ 0.0	1,568.2	(636.7)	(18.8)
Beginning balance (in shares) at Dec. 31, 2021	61,660,996	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]
Exercise of stock options and distribution of restricted stock units(in shares)	404,133
Net loss	$ (234.1)
Ending balance (in shares) at Sep. 30, 2022	69,120,346	69,120,346
Ending balance at Sep. 30, 2022	$ 906.8	$ 0.0	1,738.1	(796.0)	(35.3)
Beginning balance (in shares) at Mar. 31, 2022		61,758,739
Beginning balance at Mar. 31, 2022	912.7	$ 0.0	1,568.2	(636.7)	(18.8)
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Exercise of stock options and distribution of restricted stock units(in shares)		108,838
Exercise of stock options and distribution of restricted stock units	0.4		0.4
Stock-based compensation	13.9		13.9
Net loss	(67.9)			(67.9)
Other comprehensive income (loss)	(10.0)				(10.0)
Ending balance (in shares) at Jun. 30, 2022		61,867,577
Ending balance at Jun. 30, 2022	849.1	$ 0.0	1,582.5	(704.6)	(28.8)
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Issuances of common stock from acquisition of Metromile(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)		350,835
Exercise of stock options and distribution of restricted stock units	2.3		2.3
Stock-based compensation	15.6		15.6
Net loss	(91.4)			(91.4)
Other comprehensive income (loss)	$ (6.5)				(6.5)
Ending balance (in shares) at Sep. 30, 2022	69,120,346	69,120,346
Ending balance at Sep. 30, 2022	$ 906.8	$ 0.0	$ 1,738.1	$ (796.0)	$ (35.3)