Consolidated Statements Of Operations and Comprehensive Income (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenues
Net premiums written	$ 17,025	$ 16,075	$ 15,372
(Increase) decrease in unearned premiums	(412)	(398)	15
Net premiums earned	16,613	15,677	15,387
Net investment income	2,144	2,181	2,242
Net realized gains (losses):
Other-than-temporary impairment (OTTI) losses gross	(22)	(38)	(65)
Portion of OTTI losses recognized in other comprehensive income (OCI)	0	1	15
Net OTTI losses recognized in income	(22)	(37)	(50)
Net realized gains (losses) excluding OTTI losses	526	115	(745)
Total net realized gains (losses)	504	78	(795)
Total revenues	19,261	17,936	16,834
Expenses
Losses and loss expenses	9,348	9,653	9,520
Policy benefits	515	521	401
Policy acquisition costs	2,659	2,446	2,472
Administrative expenses	2,211	2,096	2,068
Interest expense	275	250	250
Other (income) expense	15	(6)	81
Total expenses	15,023	14,960	14,792
Income before income tax	4,238	2,976	2,042
Income tax expense	480	270	502
Net income	3,758	2,706	1,540
Other comprehensive income (loss)
Unrealized appreciation (depreciation)	(1,762)	1,350	646
Reclassification adjustment for net realized gains included in net income	(105)	(234)	(173)
Other comprehensive income (loss)after reclassification for net realized gains included in net income	(1,867)	1,116	473
Change in:
Cumulative translation adjustment	(339)	116	(5)
Pension liability	0	(35)	8
Other comprehensive income (loss), before income tax	(2,206)	1,197	476
Income tax benefit (expense) related to OCI items	471	(221)	(159)
Other comprehensive income (loss)	(1,735)	976	317
Comprehensive income	$ 2,023	$ 3,682	$ 1,857
Earnings per share
Basic earnings per share	$ 11.02	$ 7.96	$ 4.55
Diluted earnings per share	$ 10.92	$ 7.89	$ 4.52