Segment Information (Operations By Segment) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Net premiums written									$ 16,075	$ 15,372	$ 13,708
Net premiums earned	3,848	4,665	3,783	3,381	3,831	4,490	3,757	3,309	15,677	15,387	13,504
Losses and loss expenses	2,683	3,047	2,119	1,804	2,286	2,745	2,226	2,263	9,653	9,520	7,579
Policy benefits	142	130	102	147	119	83	108	91	521	401	357
Policy acquisition costs									2,446	2,472	2,345
Administrative expenses									2,096	2,068	1,873
Underwriting income (loss)									961	926	1,350
Net investment income	567	533	537	544	565	564	569	544	2,181	2,242	2,070
Net realized gains (losses) including OTTI	272	(60)	(394)	260	83	(760)	(73)	(45)	78	(795)	432
Interest expense									250	250	224
Other (income) expense									(6)	81	(10)
(Gains) losses from fair value changes in separate account assets									(29)	36
Other									23	45
Income tax expense (benefit)									270	502	553
Net income (loss)	765	640	328	973	735	(39)	594	250	2,706	1,540	3,085
Insurance - North American
Segment Reporting Information [Line Items]
Net premiums written									7,208	6,851	5,797
Net premiums earned									7,019	6,911	5,651
Losses and loss expenses									5,626	5,276	3,918
Policy benefits
Policy acquisition costs									586	612	626
Administrative expenses									601	592	561
Underwriting income (loss)									206	431	546
Net investment income									1,091	1,170	1,138
Net realized gains (losses) including OTTI									42	34	417
Interest expense									12	15	9
Other (income) expense											(22)
(Gains) losses from fair value changes in separate account assets										0
Other									(9)	5
Income tax expense (benefit)									200	395	435
Net income (loss)									1,136	1,220	1,679
Insurance - Overseas General
Segment Reporting Information [Line Items]
Net premiums written									5,863	5,629	5,189
Net premiums earned									5,740	5,614	5,153
Losses and loss expenses									2,862	3,029	2,615
Policy benefits
Policy acquisition costs									1,353	1,335	1,209
Administrative expenses									935	939	837
Underwriting income (loss)									590	311	492
Net investment income									521	546	473
Net realized gains (losses) including OTTI									103	33	123
Interest expense									5	5	1
Other (income) expense											(13)
(Gains) losses from fair value changes in separate account assets
Other									3
Income tax expense (benefit)									133	164	171
Net income (loss)									1,073	721	929
Global Reinsurance
Segment Reporting Information [Line Items]
Net premiums written									1,025	979	1,075
Net premiums earned									1,002	1,003	1,071
Losses and loss expenses									553	621	518
Policy benefits
Policy acquisition costs									172	185	204
Administrative expenses									51	52	55
Underwriting income (loss)									226	145	294
Net investment income									290	287	288
Net realized gains (losses) including OTTI									6	(50)	93
Interest expense									4	2
Other (income) expense											(23)
(Gains) losses from fair value changes in separate account assets
Other									(15)	(1)
Income tax expense (benefit)									15	30	42
Net income (loss)									518	351	656
Life
Segment Reporting Information [Line Items]
Management underwriting income loss Insurance									402
Net premiums written									1,979	1,913	1,647
Net premiums earned									1,916	1,859	1,629
Losses and loss expenses									611	593	528
Policy benefits									521	401	357
Policy acquisition costs									334	339	306
Administrative expenses									328	317	246
Underwriting income (loss)									122	209	192
Net investment income									251	226	174
Net realized gains (losses) including OTTI									(72)	(806)	(192)
Interest expense									12	11	3
Other (income) expense											26
(Gains) losses from fair value changes in separate account assets									(29)	36
Other									25	26
Income tax expense (benefit)									58	50	59
Net income (loss)									235	(494)	86
Corporate and Other
Segment Reporting Information [Line Items]
Net premiums written
Net premiums earned
Losses and loss expenses									1	1
Policy benefits
Policy acquisition costs									1	1
Administrative expenses									181	168	174
Underwriting income (loss)									(183)	(170)	(174)
Net investment income									28	13	(3)
Net realized gains (losses) including OTTI									(1)	(6)	(9)
Interest expense									217	217	211
Other (income) expense											22
(Gains) losses from fair value changes in separate account assets
Other									19	15
Income tax expense (benefit)									(136)	(137)	(154)
Net income (loss)									$ (256)	$ (258)	$ (265)