Segment Information (Operations By Segment) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Segment Reporting Information [Line Items]
Net premiums written	$ 4,185	$ 3,798
Net premiums earned	3,970	3,573
Losses and loss expenses	2,161	1,926
Policy benefits	114	131
Policy acquisition costs	728	614
Administrative expenses	535	514
Underwriting income (loss)	432	388
Net investment income	553	531
Net realized gains (losses) including OTTI	(104)	206
Interest expense	71	60
(Gains) losses from fair value changes in separate account assets	6	(4)
Other	(23)	(6)
Other (income) expense	(17)	(10)
Income tax expense (benefit)	93	122
Net income (loss)	734	953
Insurance - North American P&C [Member]
Segment Reporting Information [Line Items]
Net premiums written	1,418	1,284
Net premiums earned	1,487	1,338
Losses and loss expenses	940	878
Policy acquisition costs	159	143
Administrative expenses	161	125
Underwriting income (loss)	227	192
Net investment income	270	251
Net realized gains (losses) including OTTI	(9)	26
Interest expense	3	(2)
Other	(20)	(15)
Income tax expense (benefit)	83	94
Net income (loss)	422	392
Insurance - North American Agriculture [Member]
Segment Reporting Information [Line Items]
Underwriting Income Including Losses Related to Crop Derivatives	(31)
Net premiums written	194	113
Net premiums earned	103	52
Losses and loss expenses	126	32
Policy acquisition costs	5	4
Administrative expenses	1	5
Underwriting income (loss)	(29)	11
Net investment income	7	6
Net realized gains (losses) including OTTI	(2)	0
Interest expense	0	0
Other	8	8
Income tax expense (benefit)	(7)	2
Net income (loss)	(25)	7
Crop Derivative Reclassification	2
Insurance - Overseas General [Member]
Segment Reporting Information [Line Items]
Net premiums written	1,771	1,620
Net premiums earned	1,612	1,459
Losses and loss expenses	817	747
Policy acquisition costs	386	339
Administrative expenses	250	236
Underwriting income (loss)	159	137
Net investment income	132	132
Net realized gains (losses) including OTTI	(10)	34
Interest expense	1	1
Other	(6)	(1)
Income tax expense (benefit)	37	46
Net income (loss)	249	257
Global Reinsurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	308	279
Net premiums earned	284	247
Losses and loss expenses	126	106
Policy acquisition costs	67	48
Administrative expenses	14	12
Underwriting income (loss)	77	81
Net investment income	77	72
Net realized gains (losses) including OTTI	(8)	20
Interest expense	1	1
Other	(19)	(8)
Income tax expense (benefit)	10	8
Net income (loss)	154	172
Life [Member]
Segment Reporting Information [Line Items]
Life underwriting income	98
Net premiums written	494	502
Net premiums earned	484	477
Losses and loss expenses	151	157
Policy benefits	114	131
Policy acquisition costs	111	80
Administrative expenses	68	85
Underwriting income (loss)	40	24
Net investment income	64	63
Net realized gains (losses) including OTTI	(76)	127
Interest expense	3	4
(Gains) losses from fair value changes in separate account assets	6	(4)
Other	7	0
Income tax expense (benefit)	10	13
Net income (loss)	2	201
Corporate And Other [Member]
Segment Reporting Information [Line Items]
Losses and loss expenses	1	6
Policy acquisition costs		0
Administrative expenses	41	51
Underwriting income (loss)	(42)	(57)
Net investment income	3	7
Net realized gains (losses) including OTTI	1	(1)
Interest expense	63	56
Other	7	10
Income tax expense (benefit)	(40)	(41)
Net income (loss)	$ (68)	$ (76)