Segment Information (Financial Data By Reportable Segment) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Segment Reporting Information [Line Items]
Operating revenue	$ 17,644.8	$ 17,435.1
Operating gain (loss)	1,118.7	1,357.3
Commercial and Specialty Business [Member]
Segment Reporting Information [Line Items]
Operating revenue	9,697.5	9,859.4
Operating gain (loss)	886.1	1,262.1
Government Business [Member]
Segment Reporting Information [Line Items]
Operating revenue	7,941.3	7,569.4
Operating gain (loss)	239.6	102.6
Other [Member]
Segment Reporting Information [Line Items]
Operating revenue	6.0	6.3
Operating gain (loss)	$ (7.0)	$ (7.4)