Corporate Investments and Funds Held For Clients (Classification Of Corporate Investments On The Consolidated Balance Sheets) (Details) - USD ($) $ in Millions		Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Corporate Investments And Funds Held For Clients [Abstract]
Cash and cash equivalents		$ 1,500.4	$ 1,949.2	$ 2,785.6
Short-term marketable securities		7.2	10.5
Long-term marketable securities	[1]	0.0	261.4
Total corporate investments		$ 1,507.6	$ 2,221.1

[1] (a) - Long-term marketable securities are included within Other assets on the Consolidated Balance Sheets.