Reinsurance (Summary Of Net Premiums Written And Earned By Segment) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Net Premiums Written And Earned By Segment [Line Items]
Premiums Written Net	$ 66,020.8	$ 56,567.4	$ 56,286.0
Premiums Earned Net	66,119.1	56,496.7	55,969.6
Commercial and Specialty Business [Member]
Net Premiums Written And Earned By Segment [Line Items]
Premiums Written Net	35,126.0	35,352.1	36,476.3
Premiums Earned Net	35,159.8	35,251.9	36,436.7
Government Business [Member]
Net Premiums Written And Earned By Segment [Line Items]
Premiums Written Net	30,894.8	21,215.3	19,809.7
Premiums Earned Net	30,959.3	21,244.8	19,532.9
Other [Member]
Net Premiums Written And Earned By Segment [Line Items]
Premiums Written Net	0	0	0
Premiums Earned Net	$ 0	$ 0	$ 0