Segment Information (Financial Data By Reportable Segment) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]
Operating revenue	$ 70,191.4	$ 60,514.0	$ 59,865.2
Operating gain (loss)	4,001.4	3,619.9	3,782.1
Depreciation and amortization of property and equipment	457.1	363.5	300.3
Commercial and Specialty Business [Member]
Segment Reporting Information [Line Items]
Operating revenue	38,790.1	38,852.9	39,961.2
Operating gain (loss)	3,093.3	3,339.7	3,344.5
Depreciation and amortization of property and equipment	0	0	0
Government Business [Member]
Segment Reporting Information [Line Items]
Operating revenue	31,366.7	21,625.7	19,874.0
Operating gain (loss)	927.1	341.8	461.6
Depreciation and amortization of property and equipment	0	0	0
Other [Member]
Segment Reporting Information [Line Items]
Operating revenue	34.6	35.4	30.0
Operating gain (loss)	(19.0)	(61.6)	(24.0)
Depreciation and amortization of property and equipment	$ 457.1	$ 363.5	$ 300.3