Goodwill And Other Intangible Assets (Summary Of The Change In The Carrying Amount Of Goodwill By Reportable Segment) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Change in the carrying amount of goodwill by reportable segment
Goodwill, Beginning Balance	$ 17,562.2	$ 17,082.0
Other adjustments	(1.0)
Acquisitions		480.2
Goodwill, Ending Balance	17,561.2	17,562.2
Accumulated impairment as of December 31	(41.0)
Commercial and Specialty Business [Member]
Change in the carrying amount of goodwill by reportable segment
Goodwill, Beginning Balance	11,818.9	11,818.9
Other adjustments	(1.0)
Acquisitions		0.0
Goodwill, Ending Balance	11,817.9	11,818.9
Accumulated impairment as of December 31	(41.0)
Government Business [Member]
Change in the carrying amount of goodwill by reportable segment
Goodwill, Beginning Balance	5,743.3	5,263.1
Other adjustments	0.0
Acquisitions		480.2
Goodwill, Ending Balance	5,743.3	$ 5,743.3
Accumulated impairment as of December 31	$ 0.0