Segment Information (Financial Data By Reportable Segment) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Operating revenue	$ 21,125.2	$ 19,771.4	$ 62,709.1	$ 58,381.1
Operating gain (loss)	1,078.1	1,221.9	4,148.7	4,313.3
Commercial and Specialty Business [Member]
Segment Reporting Information [Line Items]
Operating revenue	9,656.8	9,433.1	29,064.9	28,168.2
Operating gain (loss)	637.7	619.2	3,006.0	2,798.2
Government Business [Member]
Segment Reporting Information [Line Items]
Operating revenue	11,462.4	10,333.1	33,627.4	30,198.2
Operating gain (loss)	478.9	626.6	1,254.4	1,560.7
Other [Member]
Segment Reporting Information [Line Items]
Operating revenue	6.0	5.2	16.8	14.7
Operating gain (loss)	$ (38.5)	$ (23.9)	$ (111.7)	$ (45.6)