Investments - Schedule of Fair Value of Foreign Currency Exchange Forward Contracts (Detail) - Foreign Currency Exchange Forward Contracts - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Schedule of Investments [Line Items]
Foreign currency exchange, notional amount	$ 167.8	$ 283.2
Foreign currency exchange, fair value	0.8	5.2
Operational currency exposure
Schedule of Investments [Line Items]
Foreign currency exchange, notional amount	125.7	148.2
Foreign currency exchange, fair value	1.7	5.8
Asset manager investment exposure
Schedule of Investments [Line Items]
Foreign currency exchange, notional amount	42.1	135.0
Foreign currency exchange, fair value	$ (0.9)	$ (0.6)