Corporate Investments and Funds Held For Clients - Summary of Unrealized Losses and Fair Values of Available-for-Sale Securities that have been in Unrealized Loss Position for Period of Less than and Greater than 12 Months (Details) - Available-for-sale Securities [Member] - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024
Corporate Investments And Funds Held For Clients [Line Items]
Securities in unrealized loss position for less than 12 months, Gross unrealized losses	$ (0.1)	$ (0.2)
Securities in unrealized loss position for less than 12 months, Fair value	396.3	24.7
Gross unrealized losses	(0.1)	(0.2)
Fair value	396.3	24.7
U.S. Treasury Securities [Member]
Corporate Investments And Funds Held For Clients [Line Items]
Securities in unrealized loss position for less than 12 months, Gross unrealized losses	(0.1)	(0.2)
Securities in unrealized loss position for less than 12 months, Fair value	396.3	24.7
Gross unrealized losses	(0.1)	(0.2)
Fair value	$ 396.3	$ 24.7