Corporate Investments and Funds Held For Clients (Expected Maturities Of Available-For-Sale Securities) (Details) $ in Millions	Mar. 31, 2017 USD ($)
Corporate Investments And Funds Held For Clients [Abstract]
One year or less	$ 3,006.6
One year to two years	2,562.6
Two years to three years	4,923.3
Three years to four years	5,231.7
After four years	6,064.2
Total available-for-sale securities	$ 21,788.4