Segment Information (Operations By Segment) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Segment Reporting Information [Line Items]
Net investment income	$ 533	$ 564	$ 1,614	$ 1,677
(Gains) losses from fair value changes in separate account assets	(14)	39	(18)	39
Net premiums written	4,716	4,343	12,418	11,742
Net premiums earned	4,665	4,490	11,829	11,556
Losses and loss expenses	3,047	2,745	6,970	7,234
Policy benefits	130	83	379	282
Policy acquisition costs	609	669	1,810	1,840
Administrative expenses	519	520	1,543	1,537
Underwriting income (loss)	360	473	1,127	663
Net realized gains (losses) including OTTI	(60)	(760)	(194)	(878)
Interest expense	63	62	187	187
Other	(3)	50	32	49
Income tax expense (benefit)	147	165	405	382
Net income (loss)	640	(39)	1,941	805
Other (income) expense	(17)	89	14	88
Insurance - North American [Member]
Segment Reporting Information [Line Items]
Net investment income	263	291	808	886
Net premiums written	2,537	2,207	5,690	5,227
Net premiums earned	2,472	2,299	5,411	5,249
Losses and loss expenses	2,110	1,838	4,122	4,065
Policy acquisition costs	160	174	444	455
Administrative expenses	148	153	448	448
Underwriting income (loss)	54	134	397	281
Net realized gains (losses) including OTTI	(1)	(2)	16	8
Interest expense	3	4	9	11
Other	(5)	21	4	8
Income tax expense (benefit)	81	120	279	304
Net income (loss)	237	278	929	852
Insurance - Overseas General [Member]
Segment Reporting Information [Line Items]
Net investment income	127	138	386	406
Net premiums written	1,384	1,398	4,387	4,251
Net premiums earned	1,432	1,471	4,243	4,164
Losses and loss expenses	622	671	2,030	2,244
Policy acquisition costs	329	353	996	989
Administrative expenses	234	236	696	698
Underwriting income (loss)	247	211	521	233
Net realized gains (losses) including OTTI	13	1	59	(18)
Interest expense	2	2	4	4
Other	(3)	10	3	3
Income tax expense (benefit)	77	56	166	112
Net income (loss)	311	282	793	502
Global Reinsurance [Member]
Segment Reporting Information [Line Items]
Net investment income	72	70	213	213
Net premiums written	307	250	879	847
Net premiums earned	281	240	748	754
Losses and loss expenses	151	94	355	485
Policy acquisition costs	40	50	125	143
Administrative expenses	13	12	38	38
Underwriting income (loss)	77	84	230	88
Net realized gains (losses) including OTTI	(2)	(29)	(6)	(56)
Interest expense	1	0	3	1
Other	(5)	7	(7)	2
Income tax expense (benefit)	11	7	17	25
Net income (loss)	140	111	424	217
Life [Member]
Segment Reporting Information [Line Items]
Management underwriting income loss Insurance	102
Net investment income	63	60	186	166
(Gains) losses from fair value changes in separate account assets	(14)	39	(18)	39
Net premiums written	488	488	1,462	1,417
Net premiums earned	480	480	1,427	1,389
Losses and loss expenses	164	142	463	439
Policy benefits	130	83	379	282
Policy acquisition costs	80	92	244	253
Administrative expenses	81	81	237	233
Underwriting income (loss)	25	82	104	182
Net realized gains (losses) including OTTI	(71)	(732)	(261)	(813)
Interest expense	3	3	9	9
Other	0	10	14	27
Income tax expense (benefit)	14	13	44	41
Net income (loss)	14	(655)	(20)	(581)
Corporate And Other [Member]
Segment Reporting Information [Line Items]
Net investment income	8	5	21	6
Losses and loss expenses		0		1
Policy acquisition costs			1
Administrative expenses	43	38	124	120
Underwriting income (loss)	(43)	(38)	(125)	(121)
Net realized gains (losses) including OTTI	1	2	(2)	1
Interest expense	54	53	162	162
Other	10	2	18	9
Income tax expense (benefit)	(36)	(31)	(101)	(100)
Net income (loss)	$ (62)	$ (55)	$ (185)	$ (185)