Corporate Investments and Funds Held for Clients (Schedule of Investment of Funds Held for Clients) (Details) - USD ($) $ in Millions	Sep. 30, 2023		Jun. 30, 2023	Sep. 30, 2022	[1]
Debt Securities, Available-for-sale [Line Items]
Restricted cash and cash equivalents held to satisfy client funds obligations	$ 5,520.5	[1]	$ 6,688.0	$ 4,368.3
Total funds held for clients	34,762.9		36,333.6
Current
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, restricted	6,061.5		5,601.9
Non-current
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, restricted	$ 23,180.9		$ 24,043.7

[1] See Note 6 for a reconciliation of restricted cash and restricted cash equivalents in funds held for clients on the Consolidated Balance Sheets.