Investments - Schedule of Fair Value of Foreign Currency Exchange Forward Contracts (Detail) - Foreign Currency Exchange Forward Contracts - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Schedule of Investments [Line Items]
Foreign currency exchange, notional amount	$ 313.8	$ 311.8
Foreign currency exchange, fair value	0.4	(0.6)
Operational currency exposure
Schedule of Investments [Line Items]
Foreign currency exchange, notional amount	288.8	276.3
Foreign currency exchange, fair value	(3.4)	(0.3)
Asset manager investment exposure
Schedule of Investments [Line Items]
Foreign currency exchange, notional amount	25.0	35.5
Foreign currency exchange, fair value	$ 3.8	$ (0.3)