Corporate Investments and Funds Held For Clients (Expected Maturities Of Available-For-Sale Securities) (Details) $ in Millions	Mar. 31, 2019 USD ($)
Corporate Investments And Funds Held For Clients [Abstract]
One year or less	$ 4,563.5
One year to two years	5,733.7
Two years to three years	4,493.0
Three years to four years	4,327.5
After four years	4,585.7
Total available-for-sale securities	$ 23,703.4