Corporate Investments and Funds Held For Clients (Classification Of Corporate Investments On The Consolidated Balance Sheets) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Corporate Investments And Funds Held For Clients [Abstract]
Cash and cash equivalents	$ 1,602.2	$ 1,908.5	$ 1,500.4
Short-term marketable securities	10.6	0.0
Long-term marketable securities	0.0	13.6
Total corporate investments	$ 1,612.8	$ 1,922.1