Corporate Investments and Funds Held for Clients (Classification of Corporate Investments on the Consolidated Balance Sheets) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Jun. 30, 2023	Sep. 30, 2022
Corporate Investments And Funds Held For Clients [Abstract]
Cash and cash equivalents	$ 1,441.4	$ 2,083.5	$ 1,207.7
Short-term marketable securities	146.8	14.7
Long-term marketable securities	211.2	104.6
Total corporate investments	$ 1,799.4	$ 2,202.8