CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash flows from operating activities:
Net loss	$ (297.8)	$ (241.3)	$ (122.3)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	12.2	3.7	1.7
Stock-based compensation	59.3	44.1	10.6
Amortization of premium (discount) on bonds	6.7	(4.2)	(0.4)
Provision for bad debt	8.7	6.2	2.2
Common shares contribution to Lemonade Foundation	0.0	0.0	12.2
Unrealized loss on money market funds	0.0	0.0	0.1
Changes in operating assets and liabilities:
Premium receivable	(43.8)	(47.2)	(34.2)
Reinsurance recoverable	(52.6)	(40.8)	(28.7)
Prepaid reinsurance premium	(14.9)	(58.3)	(90.3)
Deferred acquisition costs	(0.8)	(2.7)	(1.7)
Other assets	(7.0)	(38.6)	(12.0)
Unpaid losses and loss adjustment expenses	74.0	51.6	18.1
Unearned premium	65.1	83.9	55.8
Trade payables	(0.7)	(0.4)	0.7
Funds held for reinsurance treaties	32.9	41.0	62.1
Deferred ceding commission	3.2	14.1	22.4
Ceded premium payable	(12.4)	5.7	9.1
Other liabilities and accrued expenses	4.9	38.6	2.9
Net cash used in operating activities	(163.0)	(144.6)	(91.7)
Cash flows from investing activities:
Acquisition of business, net of cash acquired	98.8	0.0	0.0
Proceeds from short-term investments sold or matured	224.5	20.2	70.0
Proceeds from bonds sold or matured	138.0	27.2	2.3
Cost of short-term investments acquired	(136.7)	(130.8)	(14.9)
Cost of bonds acquired	(133.4)	(712.0)	(2.9)
Purchases of property and equipment	(10.1)	(9.4)	(4.4)
Net cash provided by (used in) investing activities	181.1	(804.8)	50.1
Cash flows from financing activities:
Proceeds from Initial Public Offering and Follow-on Offering, net of underwriting discounts and commissions and offering costs	0.0	640.3	338.0
Proceeds from release of shares upon repayment	0.0	0.0	1.3
Proceeds from stock exercises	3.6	9.3	1.8
Net cash provided by financing activities	3.6	649.6	341.1
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(5.8)	(1.0)	1.6
Net increase (decrease) in cash, cash equivalents and restricted cash	15.9	(300.8)	301.1
Cash, cash equivalents and restricted cash at beginning of year	270.6	571.4	270.3
Cash, cash equivalents and restricted cash at end of year	286.5	270.6	571.4
Supplemental disclosure of cash flow information:
Cash paid for income taxes	3.4	3.2	1.6
Non-cash transactions:
Warrants assumed from acquisition of Metromile	$ 0.3	$ 0.0	$ 0.0