Income Taxes - Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Deferred tax liabilities
Investments	$ (0.5)	$ (0.5)
Total deferred tax liabilities	(0.5)	(0.5)
Deferred tax assets
Deferred tax asset related to investments	278.2	148.9
Net operating loss carryforwards	46.2	28.3
Total deferred tax assets	324.4	177.2
Net deferred tax assets (liabilities)	$ 323.9	$ 176.7