Consolidated Statements Of Operations and Comprehensive Income (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Revenues
Net premiums written	$ 4,185	$ 3,798
Increase in unearned premiums	(215)	(225)
Net premiums earned	3,970	3,573
Net investment income	553	531
Net realized gains (losses):
Other-than-temporary impairment (OTTI) losses gross	(12)	(3)
Portion of OTTI losses recognized in other comprehensive income (OCI)	1	0
Net OTTI losses recognized in income	(11)	(3)
Net realized gains (losses) excluding OTTI losses	(93)	209
Total net realized gains (losses)	(104)	206
Total revenues	4,419	4,310
Expenses
Losses and loss expenses	2,161	1,926
Policy benefits	114	131
Policy acquisition costs	728	614
Administrative expenses	535	514
Interest expense	71	60
Other (income) expense	(17)	(10)
Total expenses	3,592	3,235
Income before income tax	827	1,075
Income tax expense (includes $(3) and $5 income tax (benefit) expense from reclassification of unrealized gains)	93	122
Net income	734	953
Other comprehensive income (loss)
Unrealized appreciation (depreciation)	519	(116)
Reclassification adjustment for net realized gains included in net income	(6)	(35)
Unrealized appreciation (Depreciation) after reclassification adjustment	513	(151)
Change in:
Cumulative translation adjustment	(33)	(211)
Pension liability	(8)	22
Other comprehensive income (loss), before income tax	472	(340)
Income tax (expense) benefit related to OCI items	(98)	103
Other comprehensive income (loss)	374	(237)
Comprehensive income	1,108	716
Earnings per share
Basic earnings per share	$ 2.16	$ 2.80
Diluted earnings per share	$ 2.14	$ 2.77
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Net realized gains (losses):
Total net realized gains (losses)	6	35
Expenses
Income tax expense (includes $(3) and $5 income tax (benefit) expense from reclassification of unrealized gains)	$ (3)	$ 5