Corporate Investments and Funds Held For Clients (Expected Maturities Of Available-For-Sale Securities) (Details) $ in Millions	Dec. 31, 2018 USD ($)
Corporate Investments And Funds Held For Clients [Abstract]
One year or less	$ 3,776.8
One year to two years	5,181.1
Two years to three years	4,993.5
Three years to four years	4,323.9
After four years	4,642.8
Total available-for-sale securities	$ 22,918.1