Segments Information - Revenues and Income Before Income Tax of Each Operating Segment (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Revenues
Premiums earned related to insurance business	$ 3,029	$ 3,005
Investment Income	358	372
Premiums earned related to reinsurance assumed		(1)
Net Premiums earned	3,029	3,004
Corporate and other	10	12
Realized investment gains, net	116	138
Total Revenues	3,506	3,517
Insurance underwriting income (loss)	195	440
Reinsurance assumed underwriting income		4
Underwriting income before deferred policy acquisition costs	195	444
Increase in deferred policy acquisition costs	13	41
Underwriting income	208	485
Total property and casualty insurance	547	841
Corporate and other	(60)	(63)
Realized investment gains, net	116	138
Income Before Federal and Foreign Income Tax	603	916
Property and Casualty Insurance [Member]
Revenues
Investment Income	351	363
Total Revenues	3,380	3,367
Investment income	341	351
Other income (charges)	(2)	5
Operating Segments [Member] | Personal Insurance [Member]
Revenues
Premiums earned related to insurance business	1,076	1,031
Insurance underwriting income (loss)	2	150
Operating Segments [Member] | Commercial Insurance [Member]
Revenues
Premiums earned related to insurance business	1,300	1,308
Insurance underwriting income (loss)	111	195
Operating Segments [Member] | Specialty Insurance [Member]
Revenues
Premiums earned related to insurance business	653	666
Insurance underwriting income (loss)	$ 82	$ 95