Corporate Investments and Funds Held For Clients (Expected Maturities Of Available-For-Sale Securities) (Details) $ in Millions	Dec. 31, 2016 USD ($)
Corporate Investments And Funds Held For Clients [Abstract]
One year or less	$ 3,018.3
One year to two years	2,403.8
Two years to three years	4,199.7
Three years to four years	4,768.4
After four years	7,068.5
Total available-for-sale securities	$ 21,458.7