Segment Information (Operations By Segment) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Segment Reporting [Line Items]
Net premiums written									$ 15,372	$ 13,708	$ 13,299
Net premiums earned	3,831	4,490	3,757	3,309	3,572	3,422	3,233	3,277	15,387	13,504	13,240
Losses and loss expenses	2,286	2,745	2,226	2,263	1,971	1,887	1,800	1,921	9,520	7,579	7,422
Policy benefits	119	83	108	91	90	93	87	87	401	357	325
Policy acquisition costs									2,447	2,337	2,130
Administrative expenses									2,052	1,858	1,811
Underwriting income (loss)									967	1,373	1,552
Net investment income	565	564	569	544	532	516	518	504	2,242	2,070	2,031
Net realized gains (losses) including OTTI	83	(760)	(73)	(45)	305	(50)	9	168	(795)	432	(196)
Interest expense									250	224	225
Losses from separate account assets									36
Other (income) expense									73	(16)	85
Other									37
Income tax expense (benefit)									506	559	528
Net income	750	(31)	607	259	1,001	675	677	755	1,585	3,108	2,549
Insurance - North American [Member]
Segment Reporting [Line Items]
Net premiums written									6,851	5,797	5,641
Net premiums earned									6,911	5,651	5,684
Losses and loss expenses									5,276	3,918	4,013
Policy acquisition costs									613	625	517
Administrative expenses									592	561	572
Underwriting income (loss)									430	547	582
Net investment income									1,170	1,138	1,094
Net realized gains (losses) including OTTI									34	417	10
Interest expense									15	9	1
Other (income) expense										(22)	36
Other									5
Income tax expense (benefit)									394	436	384
Net income									1,220	1,679	1,265
Insurance - Overseas General [Member]
Segment Reporting [Line Items]
Net premiums written									5,756	5,280	5,145
Net premiums earned									5,737	5,240	5,147
Losses and loss expenses									3,073	2,647	2,597
Policy benefits										4	4
Policy acquisition costs									1,393	1,251	1,202
Administrative expenses									945	840	783
Underwriting income (loss)									326	498	561
Net investment income									548	475	479
Net realized gains (losses) including OTTI									33	123	(20)
Interest expense									5	1
Other (income) expense										(13)	20
Income tax expense (benefit)									169	173	186
Net income									733	935	814
Global Reinsurance [Member]
Segment Reporting [Line Items]
Net premiums written									979	1,075	1,038
Net premiums earned									1,003	1,071	979
Losses and loss expenses									621	518	330
Policy acquisition costs									185	204	195
Administrative expenses									52	55	55
Underwriting income (loss)									145	294	399
Net investment income									287	288	278
Net realized gains (losses) including OTTI									(50)	93	(17)
Interest expense									2
Other (income) expense										(23)	2
Other									(1)
Income tax expense (benefit)									30	42	46
Net income									351	656	612
Life [Member]
Segment Reporting [Line Items]
Net premiums written									1,786	1,556	1,475
Net premiums earned									1,736	1,542	1,430
Losses and loss expenses									549	496	482
Policy benefits									401	353	321
Policy acquisition costs									255	257	216
Administrative expenses									295	228	243
Underwriting income (loss)									236	208	168
Management underwriting income (loss) insurance									424
Net investment income									224	172	176
Net realized gains (losses) including OTTI									(806)	(192)	(15)
Interest expense									11	3
Losses from separate account assets									36
Other (income) expense										20	2
Other									18
Income tax expense (benefit)									50	62	48
Net income									(461)	103	279
Corporate And Other [Member]
Segment Reporting [Line Items]
Losses and loss expenses									1
Policy acquisition costs									1
Administrative expenses									168	174	158
Underwriting income (loss)									(170)	(174)	(158)
Net investment income									13	(3)	4
Net realized gains (losses) including OTTI									(6)	(9)	(154)
Interest expense									217	211	224
Other (income) expense										22	25
Other									15
Income tax expense (benefit)									(137)	(154)	(136)
Net income									$ (258)	$ (265)	$ (421)