Consolidated Statements Of Operations and Comprehensive Income (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Revenues
Net premiums written	$ 4,620	$ 4,716	$ 12,809	$ 12,418
Change in unearned premiums	(10)	(51)	(559)	(589)
Net premiums earned	4,610	4,665	12,250	11,829
Net investment income	522	533	1,587	1,614
Net realized gains (losses):
Other-than-temporary impairment (OTTI) losses gross	(4)	(10)	(14)	(30)
Portion of OTTI losses recognized in other comprehensive income (OCI)	0	0	0	0
Net OTTI losses recognized in income	(4)	(10)	(14)	(30)
Net realized gains (losses) excluding OTTI losses	44	(50)	364	(164)
Total net realized gains (losses)	40	(60)	350	(194)
Total revenues	5,172	5,138	14,187	13,249
Expenses
Losses and loss expenses	2,655	3,047	6,831	6,970
Policy benefits	138	130	379	379
Policy acquisition costs	678	609	1,957	1,810
Administrative expenses	563	519	1,641	1,543
Interest expense	72	63	205	187
Other (income) expense	(5)	(17)	22	14
Total expenses	4,101	4,351	11,035	10,903
Income before income tax	1,071	787	3,152	2,346
Income tax expense (includes $4 and $16 Income tax expense from reclassification of unrealized gains in the three and nine months ended September 30, 2013, respectively)	155	147	392	405
Net income	916	640	2,760	1,941
Other comprehensive income (loss)
Unrealized appreciation (depreciation)	16	731	(1,570)	1,369
Reclassification adjustment for net realized gains included in net income	24	56	97	147
Other comprehensive income	(8)	675	(1,667)	1,222
Change in:
Cumulative translation adjustment	149	190	(237)	162
Pension liability	(2)	(4)	17	(5)
Other comprehensive income (loss), before income tax	139	861	(1,887)	1,379
Income tax (expense) benefit related to OCI items	(25)	(185)	374	(276)
Other comprehensive income (loss)	114	676	(1,513)	1,103
Comprehensive income	1,030	1,316	1,247	3,044
Earnings per share
Basic earnings per share	$ 2.68	$ 1.88	$ 8.09	$ 5.71
Diluted earnings per share	$ 2.66	$ 1.86	$ 8.02	$ 5.67
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Net realized gains (losses):
Total net realized gains (losses)	24		97
Expenses
Income tax expense (includes $4 and $16 Income tax expense from reclassification of unrealized gains in the three and nine months ended September 30, 2013, respectively)	$ 4		$ 16