Investments - Schedule of Fair Value of Foreign Currency Exchange Forward Contracts (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Schedule of Investments [Line Items]
Derivative assets (liabilities), at fair value, net	$ 1.3	$ 5.2
Foreign Currency Exchange Forward Contracts | Operational currency exposure
Schedule of Investments [Line Items]
Derivative assets (liabilities), at fair value, net	1.8	5.8
Foreign Currency Exchange Forward Contracts | Asset manager investment exposure
Schedule of Investments [Line Items]
Derivative assets (liabilities), at fair value, net	$ (0.5)	$ (0.6)