Segment Information (Operations By Segment) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Segment Reporting [Line Items]
Net premiums written	$ 3,572	$ 3,446
Net premiums earned	3,381	3,309
Losses and loss expenses	1,804	2,263
Policy benefits	147	91
Policy acquisition costs	582	559
Administrative expenses	510	499
Underwriting income (loss)	338	(103)
Net investment income	544	544
Net realized gains (losses) including OTTI	260	(45)
Interest expense	62	63
Gains (losses) on fair value changes in separate account assets	(18)
Other (income) expense	(3)	(13)
Other	15
Income tax expense (benefit)	110	96
Net income	973	250
Insurance - North American [Member]
Segment Reporting [Line Items]
Net premiums written	1,293	1,285
Net premiums earned	1,287	1,346
Losses and loss expenses	849	994
Policy acquisition costs	127	136
Administrative expenses	147	148
Underwriting income (loss)	164	68
Net investment income	274	295
Net realized gains (losses) including OTTI	(1)	(11)
Interest expense	3	4
Other (income) expense		(16)
Other	(1)
Income tax expense (benefit)	91	89
Net income	344	275
Insurance - Overseas General [Member]
Segment Reporting [Line Items]
Net premiums written	1,528	1,410
Net premiums earned	1,391	1,278
Losses and loss expenses	705	852
Policy acquisition costs	335	301
Administrative expenses	229	223
Underwriting income (loss)	122	(98)
Net investment income	131	131
Net realized gains (losses) including OTTI	20	(9)
Interest expense	1	1
Other (income) expense		(2)
Income tax expense (benefit)	38	17
Net income	234	8
Global Reinsurance [Member]
Segment Reporting [Line Items]
Net premiums written	263	315
Net premiums earned	230	260
Losses and loss expenses	102	279
Policy acquisition costs	43	46
Administrative expenses	12	12
Underwriting income (loss)	73	(77)
Net investment income	71	72
Net realized gains (losses) including OTTI	13	(13)
Interest expense	1
Other (income) expense		(6)
Other	(5)
Income tax expense (benefit)	6	10
Net income	155	(22)
Life [Member]
Segment Reporting [Line Items]
Net premiums written	488	436
Net premiums earned	473	425
Losses and loss expenses	148	138
Policy benefits	147	91
Policy acquisition costs	76	76
Administrative expenses	78	74
Underwriting income (loss)	24	46
Net investment income	61	46
Net realized gains (losses) including OTTI	231	(13)
Interest expense	3	3
Gains (losses) on fair value changes in separate account assets	(18)
Other (income) expense		6
Other	9
Income tax expense (benefit)	11	14
Net income	311	56
Corporate And Other [Member]
Segment Reporting [Line Items]
Policy acquisition costs	1
Administrative expenses	44	42
Underwriting income (loss)	(45)	(42)
Net investment income	7
Net realized gains (losses) including OTTI	(3)	1
Interest expense	54	55
Other (income) expense		5
Other	12
Income tax expense (benefit)	(36)	(34)
Net income	$ (71)	$ (67)