CONSOLIDATED STATEMENTS OF CHANGES IN CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY (DEFICIT) - USD ($) $ in Millions	Total	Series C Preferred Stock	Series D Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income
Beginning balance (shares) at Dec. 31, 2018	24,445,555
Beginning balance at Dec. 31, 2018	$ 180.8
Convertible Preferred Stock
Issuance of preferred stock, net of issuance costs (in shares)		3,622	7,107,930
Issuance of preferred stock, net of issuance costs			$ 299.4
Ending balance (shares) at Dec. 31, 2019	31,557,107	8,703,846	7,107,930
Ending balance at Dec. 31, 2019	$ 480.2	$ 119.8	$ 299.4
Beginning balance (in shares) at Dec. 31, 2018				10,983,684
Beginning balance at Dec. 31, 2018	(79.1)			$ 0.0	$ 10.7	$ (89.8)	$ 0.0
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Repayment of partial recourse loan and release of shares upon repayment (shares)				105,487
Repayment of partial recourse loan and release of shares upon repayment	0.2				0.2
Exercise of stock options (in shares)				182,057
Exercise of stock options	0.5				0.5
Stock-based compensation	4.3				4.3
Net loss	(108.5)					(108.5)
Other comprehensive income	0.1						0.1
Ending balance (in shares) at Dec. 31, 2019				11,271,228
Ending balance at Dec. 31, 2019	$ (182.5)			$ 0.0	15.7	(198.3)	0.1
Convertible Preferred Stock
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 (shares) at Dec. 31, 2020	0
Ending balance at Dec. 31, 2020	$ 0.0
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Conversion of convertible preferred stock to common stock upon closing of initial public offering (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 upon closing of initial public offering (in shares)				12,650,000
Issuance of common stock upon closing of Follow-on Offering, net of underwriting discounts and commissions and offering costs of $22.8 million	338.0				338.0
Contribution to the Lemonade Foundation (in shares)				500,000
Contribution to the Lemonade Foundation	12.2				12.2
Repayment of partial recourse loan and release of shares upon repayment (shares)				513,537
Repayment of partial recourse loan and 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	$ 1.7						1.7
Ending balance (in shares) at Dec. 31, 2020	56,774,294			56,774,294
Ending balance at Dec. 31, 2020	$ 541.0			$ 0.0	859.8	(320.6)	1.8
Ending balance (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 upon closing of initial public offering (in shares)				4,018,647
Issuance of common stock upon closing of Follow-on Offering, net of underwriting discounts and commissions and offering costs of $22.8 million	$ 640.3				640.3
Exercise of stock options (in shares)	848,992			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	$ (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)