Reinsurance (Components of Earned Premiums) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Direct premiums earned	$ 9,624	$ 8,919	$ 8,434
Assumed premiums earned	306	244	145
Ceded premiums earned	2,659	2,281	1,976
Net earned premiums	7,271	6,882	6,603
Property and Casualty Insurance [Member]
Direct premiums earned	9,063	8,354	7,858
Assumed premiums earned	258	197	95
Ceded premiums earned	2,609	2,229	1,919
Net earned premiums	6,712	6,322	6,034
Accident and Health Insurance [Member]
Direct premiums earned	512	514	521
Assumed premiums earned	48	47	50
Ceded premiums earned	1	1	2
Net earned premiums	559	560	569
Life Insurance [Member]
Direct premiums earned	49	51	55
Assumed premiums earned
Ceded premiums earned	49	51	55
Net earned premiums
Percentage of assumed premiums earned to net premiums earned [Member]
Percentage of assumed premium earned to premium earned net	4.20%	3.50%	2.20%
Percentage of assumed premiums earned to net premiums earned [Member] | Property and Casualty Insurance [Member]
Percentage of assumed premium earned to premium earned net	3.80%	3.10%	1.60%
Percentage of assumed premiums earned to net premiums earned [Member] | Accident and Health Insurance [Member]
Percentage of assumed premium earned to premium earned net	8.60%	8.40%	8.80%
Percentage of assumed premiums earned to net premiums earned [Member] | Life Insurance [Member]
Percentage of assumed premium earned to premium earned net