Investments - Schedule of Fair Value of Foreign Currency Exchange Forward Contracts (Detail) - Foreign Currency Exchange Forward Contracts [Member] - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Schedule of Investments [Line Items]
Foreign currency exchange, fair value	$ 4.9	$ 1.1
Operational Currency Exposure [Member]
Schedule of Investments [Line Items]
Foreign currency exchange, fair value	7.0	(0.8)
Asset Manager Investment Exposure [Member]
Schedule of Investments [Line Items]
Foreign currency exchange, fair value	0.2	(0.3)
Total return strategy [Member]
Schedule of Investments [Line Items]
Foreign currency exchange, fair value	$ (2.3)	$ 2.2