Corporate Investments and Funds Held For Clients (Classification Of Corporate Investments On The Consolidated Balance Sheets) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2017
Corporate Investments And Funds Held For Clients [Abstract]
Cash and cash equivalents	$ 1,490.3	$ 2,170.0	$ 2,363.6
Short-term marketable securities	127.1	3.3
Long-term marketable securities	335.8	7.2
Total corporate investments	$ 1,953.2	$ 2,180.5