Corporate Investments and Funds Held For Clients (Classification Of Corporate Investments On The Consolidated Balance Sheets) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Corporate Investments And Funds Held For Clients [Abstract]
Cash and cash equivalents	$ 1,773.4	$ 2,780.4	$ 2,705.2
Short-term marketable securities	3.2	3.2
Long-term marketable securities	7.4	7.6
Total corporate investments	$ 1,784.0	$ 2,791.2