Corporate Investments and Funds Held For Clients (Expected Maturities Of Available-For-Sale Securities) (Details) $ in Millions	Mar. 31, 2020 USD ($)
Corporate Investments And Funds Held For Clients [Abstract]
One year or less	$ 5,802.2
One year to two years	4,387.0
Two years to three years	4,904.9
Three years to four years	3,369.3
After four years	5,560.2
Total available-for-sale securities	$ 24,023.6