Property Casualty Loss And Loss Expenses (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Favorable reserve development on prior accident years	$ 396,000,000	$ 285,000,000	$ 304,000,000
Net loss and loss expense reserves for asbestos and environmental claims	67,000,000	74,000,000
Environmental claims related to mold	54,000,000	62,000,000
Percentage of reserves for asbestos and environmental claims	1.80%	1.90%
Maximum [Member]
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Reinsurance retention	500,000
Life and Health Loss Reserves [Member]
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Reserve for loss and loss expenses	61,000,000	59,000,000	63,000,000
Homeowner [Member]
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Favorable reserve development on prior accident years	52,000,000
Commercial Lines [Member]
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Favorable reserve development on prior accident years	292,000,000	234,000,000	269,000,000
Increase in favorable reserve developement on prior accident	111,000,000
Commercial Lines [Member] | Workers' Compensation [Member]
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Favorable reserve development on prior accident years	74,000,000	97,000,000	39,000,000
Commercial Lines [Member] | Catastrophe Development [Member]
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Favorable reserve development on prior accident years	39,000,000
Commercial Lines [Member] | Commerical Casualty Business [Member]
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Favorable reserve development on prior accident years	$ 177,000,000	$ 132,000,000	$ 186,000,000