Segment Information (Operations By Segment) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Segment Reporting Information [Line Items]
Net premiums written	$ 4,559	$ 4,391	$ 8,744	$ 8,189
Net premiums earned	4,332	4,067	8,302	7,640
Losses and loss expenses	2,388	2,250	4,549	4,176
Policy benefits	144	110	258	241
Policy acquisition costs	758	665	1,486	1,279
Administrative expenses	566	564	1,101	1,078
Underwriting income (loss)	476	478	908	866
Net investment income	556	534	1,109	1,065
Net realized gains (losses) including OTTI	(73)	104	(177)	310
Interest expense	72	73	143	133
(Gains) losses from fair value changes in separate account assets	(17)	11	(11)	7
Other	(8)	26	(31)	20
Other (income) expense	(25)	37	(42)	27
Income tax expense (benefit)	133	115	226	237
Net income (loss)	779	891	1,513	1,844
Insurance - North American P&C [Member]
Segment Reporting Information [Line Items]
Net premiums written	1,635	1,529	3,053	2,813
Net premiums earned	1,542	1,428	3,029	2,766
Losses and loss expenses	1,016	950	1,956	1,828
Policy acquisition costs	152	142	311	285
Administrative expenses	175	159	336	284
Underwriting income (loss)	199	177	426	369
Net investment income	265	250	535	501
Net realized gains (losses) including OTTI	(11)	28	(20)	54
Interest expense	2	3	5	1
Other	(24)	(10)	(44)	(25)
Income tax expense (benefit)	91	91	174	185
Net income (loss)	384	371	806	763
Insurance - North American Agriculture [Member]
Segment Reporting Information [Line Items]
Underwriting Income Including Losses Related to Crop Derivatives	27
Net premiums written	388	453	582	566
Net premiums earned	330	351	433	403
Losses and loss expenses	287	293	413	325
Policy acquisition costs	23	20	28	24
Administrative expenses	1	3	2	8
Underwriting income (loss)	19	35	(10)	46
Net investment income	6	7	13	13
Net realized gains (losses) including OTTI	8	1	6	1
Interest expense	0	0	0	0
Other	9	8	17	16
Income tax expense (benefit)	5	8	(2)	10
Net income (loss)	19	27	(6)	34
Crop Derivative Gain or Loss	8
Insurance - Overseas General [Member]
Segment Reporting Information [Line Items]
Net premiums written	1,760	1,630	3,531	3,250
Net premiums earned	1,709	1,563	3,321	3,022
Losses and loss expenses	830	768	1,647	1,515
Policy acquisition costs	402	360	788	699
Administrative expenses	256	251	506	487
Underwriting income (loss)	221	184	380	321
Net investment income	136	136	268	268
Net realized gains (losses) including OTTI	14	8	4	42
Interest expense	1	2	2	3
Other	8	17	2	16
Income tax expense (benefit)	55	50	92	96
Net income (loss)	307	259	556	516
Global Reinsurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	278	292	586	571
Net premiums earned	261	245	545	492
Losses and loss expenses	109	93	235	199
Policy acquisition costs	60	48	127	96
Administrative expenses	14	12	28	24
Underwriting income (loss)	78	92	155	173
Net investment income	80	71	157	143
Net realized gains (losses) including OTTI	(15)	31	(23)	51
Interest expense	2	1	3	2
Other	(10)	2	(29)	(6)
Income tax expense (benefit)	10	7	20	15
Net income (loss)	141	184	295	356
Life [Member]
Segment Reporting Information [Line Items]
Life underwriting income	89
Net premiums written	498	487	992	989
Net premiums earned	490	480	974	957
Losses and loss expenses	146	145	297	302
Policy benefits	144	110	258	241
Policy acquisition costs	121	95	232	175
Administrative expenses	73	86	141	171
Underwriting income (loss)	6	44	46	68
Net investment income	66	63	130	126
Net realized gains (losses) including OTTI	(72)	36	(148)	163
Interest expense	3	4	6	8
(Gains) losses from fair value changes in separate account assets	(17)	11	(11)	7
Other	4	3	11	3
Income tax expense (benefit)	12	10	22	23
Net income (loss)	(2)	115	0	316
Corporate And Other [Member]
Segment Reporting Information [Line Items]
Losses and loss expenses	0	1	1	7
Policy acquisition costs		0		0
Administrative expenses	47	53	88	104
Underwriting income (loss)	(47)	(54)	(89)	(111)
Net investment income	3	7	6	14
Net realized gains (losses) including OTTI	3	0	4	(1)
Interest expense	64	63	127	119
Other	5	6	12	16
Income tax expense (benefit)	(40)	(51)	(80)	(92)
Net income (loss)	$ (70)	$ (65)	$ (138)	$ (141)