Segments Information - Revenues and Income Before Income Tax of Each Operating Segment (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Revenues
Premiums earned related to insurance business	$ 3,029	$ 2,977	$ 9,028	$ 8,908
Investment Income	358	383	1,098	1,174
Premiums earned related to reinsurance assumed	(2)		(2)	3
Net Premiums earned	3,027	2,977	9,026	8,911
Corporate and other	6	12	34	36
Realized investment gains, net	18		335	103
Total revenues	3,403	3,362	10,471	10,195
Insurance underwriting income (loss)	431	412	1,166	831
Reinsurance assumed underwriting income		15	10	34
Underwriting income before deferred policy acquisition costs	431	427	1,176	865
Increase (decrease) in deferred policy acquisition costs	12	(9)	69	15
Underwriting income	443	418	1,245	880
Total property and casualty insurance	782	783	2,298	2,003
Corporate and other loss	(61)	(56)	(182)	(173)
Realized investment gains, net	18		335	103
Income Before Federal and Foreign Income Tax	739	727	2,451	1,933
Personal insurance [Member]
Revenues
Premiums earned related to insurance business	1,060	1,009	3,141	3,013
Insurance underwriting income (loss)	108	155	333	374
Commercial insurance [Member]
Revenues
Premiums earned related to insurance business	1,321	1,299	3,928	3,890
Insurance underwriting income (loss)	215	194	534	263
Specialty insurance [Member]
Revenues
Premiums earned related to insurance business	648	669	1,959	2,005
Insurance underwriting income (loss)	108	63	299	194
Property and casualty insurance [Member]
Revenues
Investment Income	352	373	1,076	1,145
Total revenues	3,379	3,350	10,102	10,056
Investment income	342	364	1,042	1,117
Other income (charges)	$ (3)	$ 1	$ 11	$ 6