Segment Information (Operations By Segment) (Details) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Segment Reporting [Line Items]
Net premiums written	$ 4,343	$ 3,295	$ 11,742	$ 10,286
Net premiums earned	4,490	3,422	11,556	9,932
Losses and loss expenses	2,745	1,887	7,234	5,608
Policy benefits	83	93	282	267
Policy acquisition costs	666	607	1,825	1,697
Administrative expenses	517	433	1,526	1,356
Underwriting income (loss)	479	402	689	1,004
Net investment income	564	516	1,677	1,538
Net realized gains (losses) including OTTI	(760)	(50)	(878)	127
Interest expense	62	58	187	162
Losses from separate account assets	39		39
Other (income) expense	87	(25)	82	(26)
Other	48		43
Income tax expense	165	160	384	426
Net income (loss)	(31)	675	835	2,107
Insurance - North American [Member]
Segment Reporting [Line Items]
Net premiums written	2,207	1,445	5,227	4,278
Net premiums earned	2,299	1,444	5,249	4,140
Losses and loss expenses	1,838	1,026	4,065	2,888
Policy acquisition costs	176	165	455	447
Administrative expenses	153	112	448	407
Underwriting income (loss)	132	141	281	398
Net investment income	291	287	886	852
Net realized gains (losses) including OTTI	(2)	(2)	8	163
Interest expense	4	6	11	6
Other (income) expense		(20)		(21)
Other	21		8
Income tax expense	120	108	304	322
Net income (loss)	276	332	852	1,106
Insurance - Overseas General [Member]
Segment Reporting [Line Items]
Net premiums written	1,432	1,205	4,346	3,927
Net premiums earned	1,503	1,321	4,254	3,835
Losses and loss expenses	683	605	2,278	1,950
Policy benefits				4
Policy acquisition costs	370	326	1,030	905
Administrative expenses	237	204	703	613
Underwriting income (loss)	213	186	243	363
Net investment income	138	118	407	347
Net realized gains (losses) including OTTI	1	32	(18)	102
Interest expense	2		4
Other (income) expense		(4)		(5)
Other	10		3
Income tax expense	56	63	115	136
Net income (loss)	284	277	510	681
Global Reinsurance [Member]
Segment Reporting [Line Items]
Net premiums written	250	272	847	932
Net premiums earned	240	271	754	803
Losses and loss expenses	94	137	485	391
Policy acquisition costs	50	51	143	153
Administrative expenses	12	14	38	41
Underwriting income (loss)	84	69	88	218
Net investment income	70	71	213	213
Net realized gains (losses) including OTTI	(29)	10	(56)	69
Interest expense			1
Other (income) expense		(10)		(16)
Other	7		2
Income tax expense	7	12	25	31
Net income (loss)	111	148	217	485
Life [Member]
Segment Reporting [Line Items]
Net premiums written	454	373	1,322	1,149
Net premiums earned	448	386	1,299	1,154
Losses and loss expenses	130	119	405	379
Policy benefits	83	93	282	263
Policy acquisition costs	70	65	197	192
Administrative expenses	77	59	217	171
Underwriting income (loss)	88	50	198	149
Net investment income	60	43	165	129
Net realized gains (losses) including OTTI	(732)	(85)	(813)	(197)
Interest expense	3		9
Losses from separate account assets	39		39
Other (income) expense		5		11
Other	8		21
Income tax expense	13	16	40	46
Net income (loss)	(647)	(13)	(559)	24
Corporate And Other [Member]
Segment Reporting [Line Items]
Losses and loss expenses			1
Administrative expenses	38	44	120	124
Underwriting income (loss)	(38)	(44)	(121)	(124)
Net investment income	5	(3)	6	(3)
Net realized gains (losses) including OTTI	2	(5)	1	(10)
Interest expense	53	52	162	156
Other (income) expense		4		5
Other	2		9
Income tax expense	(31)	(39)	(100)	(109)
Net income (loss)	$ (55)	$ (69)	$ (185)	$ (189)