Segments Information - Revenues and Income Before Income Tax of Each Operating Segment (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Revenues
Premiums earned related to insurance business	$ 3,005	$ 2,948
Investment Income	372	401
Premiums earned related to reinsurance assumed	(1)	3
Net Premiums earned	3,004	2,951
Corporate and other	12	12
Realized investment gains, net	138	56
Total Revenues	3,517	3,410
Insurance underwriting income (loss)	440	278
Reinsurance assumed underwriting income	4	11
Underwriting income before deferred policy acquisition costs	444	289
Increase in deferred policy acquisition costs	41	14
Underwriting income	485	303
Total property and casualty insurance	841	682
Corporate and other loss	(63)	(59)
Realized investment gains, net	138	56
Income Before Federal and Foreign Income Tax	916	679
Personal insurance [Member]
Revenues
Premiums earned related to insurance business	1,031	990
Insurance underwriting income (loss)	150	161
Commercial insurance [Member]
Revenues
Premiums earned related to insurance business	1,308	1,286
Insurance underwriting income (loss)	195	51
Specialty insurance [Member]
Revenues
Premiums earned related to insurance business	666	672
Insurance underwriting income (loss)	95	66
Property and casualty insurance [Member]
Revenues
Investment Income	363	391
Total Revenues	3,367	3,342
Investment income	351	380
Other income (charges)	$ 5	$ (1)