Corporate Investments and Funds Held for Clients - Classification of Corporate Investments on the Consolidated Balance Sheets (Details) - USD ($) $ in Millions		Sep. 30, 2024	Jun. 30, 2024	Sep. 30, 2023
Investments, Debt and Equity Securities [Abstract]
Cash and cash equivalents		$ 2,104.9	$ 2,913.4	$ 1,441.4
Short-term marketable securities	[1]	5,242.2	384.0
Long-term marketable securities	[1]	940.6	0.0
Total corporate investments		$ 8,287.7	$ 3,297.4

[1] As of September 30, 2024, $578.6 million of short-term marketable securities, $98.8 million of long-term marketable securities and $1.7 million of cash and cash equivalents have been pledged as collateral under the Company's reverse repurchase agreements. As of June 30, 2024, $384.0 million of short-term marketable securities and $1.4 million of cash and cash equivalents have been pledged as collateral under the Company's reverse repurchase agreements (see Note 9).