Corporate Investments and Funds Held For Clients (Expected Maturities Of Available-For-Sale Securities) (Details) $ in Millions	Sep. 30, 2018 USD ($)
Corporate Investments And Funds Held For Clients [Abstract]
One year or less	$ 3,618.0
One year to two years	4,663.9
Two years to three years	5,684.7
Three years to four years	4,044.8
After four years	4,936.2
Total available-for-sale securities	$ 22,947.6