Investments - Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Millions		Mar. 31, 2023	Dec. 31, 2022
Schedule of Investments [Line Items]
Deferred compensation liabilities	[1]	$ (13.0)	$ (13.6)
Total		336.2	715.8
Money Market Funds [Member]
Schedule of Investments [Line Items]
Investments measured at fair value	[2]	293.5	674.5
Marketable Equity Securities [Member]
Schedule of Investments [Line Items]
Investments measured at fair value	[3]	24.4	24.3
Seed Capital Investments [Member]
Schedule of Investments [Line Items]
Investments measured at fair value	[3]	31.3	30.6
Quoted prices in Active Markets for Identical Assets (Level 1) [Member]
Schedule of Investments [Line Items]
Deferred compensation liabilities	[1]	(13.0)	(13.6)
Total		336.2	715.8
Quoted prices in Active Markets for Identical Assets (Level 1) [Member] | Money Market Funds [Member]
Schedule of Investments [Line Items]
Investments measured at fair value	[2]	293.5	674.5
Quoted prices in Active Markets for Identical Assets (Level 1) [Member] | Marketable Equity Securities [Member]
Schedule of Investments [Line Items]
Investments measured at fair value	[3]	24.4	24.3
Quoted prices in Active Markets for Identical Assets (Level 1) [Member] | Seed Capital Investments [Member]
Schedule of Investments [Line Items]
Investments measured at fair value	[3]	$ 31.3	$ 30.6

[1] Included in Other long-term liabilities on the Condensed Consolidated Balance Sheet

[2] Included in Cash and cash equivalents and Funds receivable and funds held on behalf of clients on the Condensed Consolidated Balance Sheet.

[3] Included in Investments on the Condensed Consolidated Balance Sheet