CONSOLIDATED STATEMENTS OF CHANGES IN CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY (DEFICIT) - USD ($) $ in Millions	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2019	31,557,107
Beginning balance at Dec. 31, 2019	$ 480.2
Increase (Decrease) in Temporary Equity [Roll Forward]
Conversion of convertible preferred stock to common stock upon closing of initial public offering (in shares)	(31,557,107)
Conversion of convertible preferred stock to common stock upon closing of Initial Public Offering	$ (480.2)
Ending balance (in shares) at Dec. 31, 2020	0
Ending balance at Dec. 31, 2020	$ 0.0
Beginning balance (in shares) at Dec. 31, 2019		11,271,228
Beginning balance at Dec. 31, 2019	(182.5)	$ 0.0	$ 15.7	$ (198.3)	$ 0.1
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Conversion of convertible preferred stock to common stock upon closing of initial public offering (in shares)		31,557,107
Conversion of convertible preferred stock to common stock upon closing of Initial Public Offering	480.2		480.2
Issuance of common stock (in shares)		12,650,000
Issuance of common stock	338.0		338.0
Contribution to the Lemonade Foundation (in shares)		500,000
Contribution to the Lemonade Foundation	12.2		12.2
Release of shares upon repayment (in shares)		513,537
Release of shares upon repayment	1.3		1.3
Exercise of stock options (in shares)		282,422
Exercise of stock options	1.8		1.8
Stock-based compensation	10.6		10.6
Net loss	(122.3)			(122.3)
Other comprehensive income (loss)	1.7				1.7
Ending balance (in shares) at Dec. 31, 2020		56,774,294
Ending balance at Dec. 31, 2020	$ 541.0	$ 0.0	859.8	(320.6)	1.8
Ending balance (in shares) at Dec. 31, 2021	0
Ending balance at Dec. 31, 2021	$ 0.0
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Issuance of common stock (in shares)		4,018,647
Issuance of common stock	640.3		640.3
Exercise of stock options (in shares)		868,055
Exercise of stock options	9.3		9.3
Stock-based compensation	44.1		44.1
Net loss	(241.3)			(241.3)
Other comprehensive income (loss)	$ (5.2)				(5.2)
Ending balance (in shares) at Dec. 31, 2021	61,660,996	61,660,996
Ending balance at Dec. 31, 2021	$ 988.2	$ 0.0	1,553.5	(561.9)	(3.4)
Ending balance (in shares) at Dec. 31, 2022	0
Ending balance at Dec. 31, 2022	$ 0.0
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 (in shares)	448,368	712,100
Exercise of stock options	$ 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	69,275,030
Ending balance at Dec. 31, 2022	$ 866.8	$ 0.0	$ 1,754.1	$ (859.7)	$ (27.6)