Investments - Investment in Fortitude (Details) - USD ($) $ in Millions			1 Months Ended					3 Months Ended	6 Months Ended
	Jun. 02, 2020	Nov. 13, 2018	Oct. 31, 2023	May 31, 2023	May 31, 2022	Mar. 31, 2022	May 31, 2020	Mar. 31, 2024	Jun. 30, 2024	Dec. 31, 2023
Schedule of Equity Method Investments [Line Items]
Investment									$ 3,179.3	$ 3,024.1
Fortitude Group Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Ownership percentage acquired		19.90%
Purchase of investment in Fortitude Re		$ 381.0
Deferred consideration, maximum								$ 95.0
Purchase price adjustment, maximum							$ 99.5
Purchase price adjustment, payable upon inability to make distribution							$ 79.6	$ 19.9
Fortitude Group Holdings, LLC | Fortitude Re | Maximum
Schedule of Equity Method Investments [Line Items]
Committed capital									18,600.0
Fortitude Group Holdings, LLC | Carlyle FRL
Schedule of Equity Method Investments [Line Items]
Ownership interest transferred	19.90%
Fortitude Group Holdings, LLC | Carlyle FRL
Schedule of Equity Method Investments [Line Items]
Ownership percentage acquired	51.60%		38.50%			97.50%
Ownership percentage	71.50%
Fortitude Group Holdings, LLC | T&D
Schedule of Equity Method Investments [Line Items]
Ownership percentage acquired	25.00%
Fortitude Group Holdings, LLC | Carlyle FRL and T&D
Schedule of Equity Method Investments [Line Items]
Ownership percentage	96.50%
Fortitude Re | Fortitude Group Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Ownership percentage		100.00%
Carlyle FRL
Schedule of Equity Method Investments [Line Items]
Equity capital raised				$ 1,000.0	$ 1,100.0	$ 2,000.0
Investment loss					$ 176.9				104.0
Investment									720.3
Investment, cost									$ 679.6
Carlyle FRL | Fortitude Group Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Ownership percentage				10.50%	13.50%
Carlyle FRL | Fortitude Group Holdings, LLC | Maximum
Schedule of Equity Method Investments [Line Items]
Ownership percentage					19.90%
Carlyle FRL | Fortitude Group Holdings, LLC | Minimum
Schedule of Equity Method Investments [Line Items]
Ownership percentage					13.50%
Carlyle FRL | T&D
Schedule of Equity Method Investments [Line Items]
Investment company, committed capital						$ 100.0