Acquisition of Business (Pro-forma Information) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Business Acquisition [Line Items]
Total Revenues	$ 1,194.9	$ 1,044.4	$ 3,375.2	$ 3,080.3
Total Expenses	1,044.4	966.6	3,065.7	2,995.8
Income from Continuing Operations before Income Taxes	$ 150.5	$ 77.8	$ 309.5	$ 84.5
Net Income Per Unrestricted Share, basic	$ 2.28	$ 0.82	$ 4.26	$ 0.85
Net Income Per Unrestricted Share, diluted	$ 2.26	$ 0.82	$ 4.23	$ 0.85
Infinity [Member]
Business Acquisition [Line Items]
Net Income	$ 147.5	$ 53.0	$ 275.5	$ 54.8