Investments - Summary of Investment Income (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	$ (134.7)	$ (93.5)	$ (198.4)	$ (159.2)	$ (167.3)
Investment expenses	(5.3)	(4.8)	(10.3)	(11.7)	(12.7)
Net investment income	129.4	88.7	188.1	147.5	154.6
Fixed income securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	(55.7)	(44.5)	(95.6)	(87.2)	(106.5)
Short-term investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	(1.6)	0.0	(0.6)	(0.1)	(0.8)
Short-term investment, Trading
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	(0.1)	0.0	(0.1)	0.0	(0.5)
Fixed term deposits (included in cash and cash equivalents)
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	(17.3)	(0.5)	(6.6)	(0.7)	(6.4)
Catastrophe bonds — Trading
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	(1.1)	(0.1)	(0.3)	(0.9)	(1.4)
Privately-held investments — Trading
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	(21.5)	(8.8)	(24.3)	(18.2)	(20.9)
Other investments, at fair value
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	10.4	(20.7)	(13.9)	(21.9)	(2.0)
Fixed Income Securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	$ (47.8)	$ (18.9)	$ (57.0)	$ (30.2)	$ (32.8)

Represents the total of interest and dividend income, including any amortization and accretion (as applicable) of discounts and premiums, earned from (1) loans and leases whether held-for-sale or held-in-portfolio; (2) investment securities; (3) federal funds sold; (4) securities purchased under agreements to resell; (5) investments in banker's acceptances, commercial paper, or certificates of deposit; (6) dividend income; or (7) other investments not otherwise specified herein.

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 220
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Amount of expenses related to the generation of investment income.

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Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

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