Corporate Investments and Funds Held For Clients (Expected Maturities Of Available-For-Sale Securities) (Details) $ in Millions	Sep. 30, 2020 USD ($)
Corporate Investments And Funds Held For Clients [Abstract]
One year or less	$ 5,617.8
One year to two years	4,283.0
Two years to three years	3,817.6
Three years to four years	2,932.7
After four years	4,554.0
Total available-for-sale securities	$ 21,205.1