Property Casualty Loss and Loss Expenses - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Favorable reserve development on prior accident years	$ 66	$ 92	$ 95	$ 102
Life and Health Loss Reserves
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Reserve for loss and loss expenses	36	65	36	65
Commercial Lines
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Favorable reserve development on prior accident years	57		60
Commercial Lines | Commerical Casualty Business [Member]
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Favorable reserve development on prior accident years	24
Commercial Lines | Commercial Property Segment [Member]
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Favorable reserve development on prior accident years	22		24
Commercial Lines | Workers Compensation [Member]
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Favorable reserve development on prior accident years			30
Personal Lines
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Favorable reserve development on prior accident years	1		18
Excess And Surplus Lines Insurance
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Favorable reserve development on prior accident years	8		17
Consolidated Property and Casualty Insurance Entity [Member] | Catastrophe Development
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Favorable reserve development on prior accident years	$ 5	$ 8	$ 14	$ 15