Corporate Investments and Funds Held for Clients - Schedule of Classification of Corporate Investments on the Consolidated Balance Sheets (Details) - USD ($) $ in Millions		Sep. 30, 2025	Jun. 30, 2025	Sep. 30, 2024
Investments, Debt and Equity Securities [Abstract]
Cash and cash equivalents		$ 2,478.0	$ 3,347.8	$ 2,104.9
Short-term marketable securities	[1]	5,466.1	4,498.8
Total corporate investments		$ 7,944.1	$ 7,846.6

[1] As of September 30, 2025, $247.4 million of short-term marketable securities have been pledged as collateral under the Company's reverse repurchase agreements. As of June 30, 2025, $38.4 million of short-term marketable securities have been pledged as collateral under the Company's reverse repurchase agreements (see Note 10).