Segment Information (Reconciliation Of Reportable Segments Operating Revenues To Total Revenues Reported In The Consolidated Statements Of Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting [Abstract]
Reportable segments operating revenues	$ 22,096.7	$ 21,125.2	$ 66,614.2	$ 62,709.1
Net investment income	220.2	200.9	627.6	566.9
Net realized gains (losses) on financial instruments	114.7	88.8	138.2	(23.8)
Other-than-temporary impairment losses recognized in income	(5.6)	(11.0)	(20.9)	(103.6)
Total revenues	$ 22,426.0	$ 21,403.9	$ 67,359.1	$ 63,148.6