Reinsurance (Components of Written Premiums) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Direct premiums written	$ 9,658		$ 9,025		$ 8,560
Assumed premiums written	296		216		152
Ceded premiums written	2,606		2,277		1,914
Net written premiums	7,348	[1]	6,964	[1]	6,798	[1]
Property and Casualty Insurance [Member]
Direct premiums written	9,103		8,467		7,976
Assumed premiums written	249		169		102
Ceded premiums written	2,556		2,225		1,857
Net written premiums	6,796		6,411		6,221
Accident and Health Insurance [Member]
Direct premiums written	506		507		529
Assumed premiums written	47		47		50
Ceded premiums written	1		1		2
Net written premiums	552		553		577
Life Insurance [Member]
Direct premiums written	49		51		55
Assumed premiums written
Ceded premiums written	49		51		55
Net written premiums
Percentage of assumed premiums written to net premiums written [Member]
Percentage of assumed premium written to premium written net	4.00%		3.10%		2.20%
Percentage of assumed premiums written to net premiums written [Member] | Property and Casualty Insurance [Member]
Percentage of assumed premium written to premium written net	3.70%		2.60%		1.60%
Percentage of assumed premiums written to net premiums written [Member] | Accident and Health Insurance [Member]
Percentage of assumed premium written to premium written net	8.50%		8.50%		8.70%
Percentage of assumed premiums written to net premiums written [Member] | Life Insurance [Member]
Percentage of assumed premium written to premium written net

[1] (a)Related to business in property and casualty companies only.