Segments Information - Revenues and Income Before Income Tax of Each Operating Segment (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
Revenues
Premiums earned related to insurance business	$ 3,063	$ 2,994	$ 6,092	$ 5,999
Investment Income	351	368	709	740
Premiums earned related to reinsurance assumed	1	1	1
Net Premiums earned	3,064	2,995	6,093	5,999
Corporate and other	8	16	18	28
Realized investment gains, net	125	179	241	317
Total Revenues	3,542	3,551	7,048	7,068
Insurance underwriting income (loss)	256	295	451	735
Reinsurance assumed underwriting income	1	6	1	10
Underwriting income before deferred policy acquisition costs	257	301	452	745
Increase in deferred policy acquisition costs	21	16	34	57
Underwriting income	278	317	486	802
Total property and casualty insurance	612	675	1,159	1,516
Corporate and other	(59)	(58)	(119)	(121)
Realized investment gains, net	125	179	241	317
Income Before Federal and Foreign Income Tax	678	796	1,281	1,712
Property and Casualty Insurance [Member]
Revenues
Investment Income	345	361	696	724
Total Revenues	3,409	3,356	6,789	6,723
Investment income	336	349	677	700
Other income (charges)	(2)	9	(4)	14
Operating Segments [Member] | Personal Insurance [Member]
Revenues
Premiums earned related to insurance business	1,102	1,050	2,178	2,081
Insurance underwriting income (loss)	45	75	47	225
Operating Segments [Member] | Commercial Insurance [Member]
Revenues
Premiums earned related to insurance business	1,305	1,299	2,605	2,607
Insurance underwriting income (loss)	71	124	182	319
Operating Segments [Member] | Specialty Insurance [Member]
Revenues
Premiums earned related to insurance business	656	645	1,309	1,311
Insurance underwriting income (loss)	$ 140	$ 96	$ 222	$ 191