Segment Information (Operations By 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
Segment Reporting Information [Line Items]
Net premiums written	$ 4,620	$ 4,716	$ 12,809	$ 12,418
Net premiums earned	4,610	4,665	12,250	11,829
Losses and loss expenses	2,655	3,047	6,831	6,970
Policy benefits	138	130	379	379
Policy acquisition costs	678	609	1,957	1,810
Administrative expenses	563	519	1,641	1,543
Underwriting income (loss)	576	360	1,442	1,127
Net investment income	522	533	1,587	1,614
Net realized gains (losses) including OTTI	40	(60)	350	(194)
Interest expense	72	63	205	187
(Gains) losses from fair value changes in separate account assets	(14)	(14)	(7)	(18)
Other	9	(3)	29	32
Other (income) expense	(5)	(17)	22	14
Income tax expense (benefit)	155	147	392	405
Net income (loss)	916	640	2,760	1,941
Insurance - North American P&C [Member]
Segment Reporting Information [Line Items]
Net premiums written	1,500	1,373	4,313	3,915
Net premiums earned	1,444	1,306	4,210	3,802
Losses and loss expenses	963	819	2,791	2,474
Policy acquisition costs	159	147	444	419
Administrative expenses	153	148	437	451
Underwriting income (loss)	169	192	538	458
Net investment income	254	257	755	789
Net realized gains (losses) including OTTI	9	(2)	63	15
Interest expense	3	3	4	9
Other	(13)	(13)	(38)	(20)
Income tax expense (benefit)	79	129	264	308
Net income (loss)	363	328	1,126	965
Insurance - North American Agriculture [Member]
Segment Reporting Information [Line Items]
Underwriting Income Including Losses Related to Crop Derivatives	65		111
Net premiums written	805	1,164	1,371	1,775
Net premiums earned	849	1,166	1,252	1,609
Losses and loss expenses	746	1,291	1,071	1,648
Policy acquisition costs	32	13	56	25
Administrative expenses	5	0	13	(3)
Underwriting income (loss)	66	(138)	112	(61)
Net investment income	6	6	19	19
Net realized gains (losses) including OTTI	0	1	1	1
Interest expense	0	0	0	0
Other	8	8	24	24
Income tax expense (benefit)	14	(48)	24	(29)
Net income (loss)	50	(91)	84	(36)
Crop Derivative Reclassification	1		1
Insurance - Overseas General [Member]
Segment Reporting Information [Line Items]
Net premiums written	1,571	1,384	4,821	4,387
Net premiums earned	1,611	1,432	4,633	4,243
Losses and loss expenses	712	622	2,227	2,030
Policy acquisition costs	349	329	1,048	996
Administrative expenses	263	234	750	696
Underwriting income (loss)	287	247	608	521
Net investment income	128	127	396	386
Net realized gains (losses) including OTTI	(8)	13	34	59
Interest expense	1	2	4	4
Other	14	(3)	30	3
Income tax expense (benefit)	78	77	174	166
Net income (loss)	314	311	830	793
Global Reinsurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	265	307	836	879
Net premiums earned	239	281	731	748
Losses and loss expenses	93	151	292	355
Policy acquisition costs	52	40	148	125
Administrative expenses	12	13	36	38
Underwriting income (loss)	82	77	255	230
Net investment income	66	72	209	213
Net realized gains (losses) including OTTI	(5)	(2)	46	(6)
Interest expense	2	1	4	3
Other	(7)	(5)	(13)	(7)
Income tax expense (benefit)	16	11	31	17
Net income (loss)	132	140	488	424
Life [Member]
Segment Reporting Information [Line Items]
Life underwriting income	92
Net premiums written	479	488	1,468	1,462
Net premiums earned	467	480	1,424	1,427
Losses and loss expenses	141	164	443	463
Policy benefits	138	130	379	379
Policy acquisition costs	86	80	261	244
Administrative expenses	85	81	256	237
Underwriting income (loss)	17	25	85	104
Net investment income	61	63	187	186
Net realized gains (losses) including OTTI	43	(71)	206	(261)
Interest expense	4	3	12	9
(Gains) losses from fair value changes in separate account assets	(14)	(14)	(7)	(18)
Other	4	0	7	14
Income tax expense (benefit)	10	14	33	44
Net income (loss)	117	14	433	(20)
Corporate And Other [Member]
Segment Reporting Information [Line Items]
Losses and loss expenses	0	0	7	0
Policy acquisition costs		0		1
Administrative expenses	45	43	149	124
Underwriting income (loss)	(45)	(43)	(156)	(125)
Net investment income	7	8	21	21
Net realized gains (losses) including OTTI	1	1	0	(2)
Interest expense	62	54	181	162
Other	3	10	19	18
Income tax expense (benefit)	(42)	(36)	(134)	(101)
Net income (loss)	$ (60)	$ (62)	$ (201)	$ (185)