Consolidated Statements Of Operations And Comprehensive Income (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Revenues
Net premiums written	$ 3,572	$ 3,446
Change in unearned premiums	(191)	(137)
Net premiums earned	3,381	3,309
Net investment income	544	544
Net realized gains (losses):
Other-than-temporary impairment (OTTI) losses gross	(10)	(5)
Portion of OTTI losses recognized in other comprehensive income (OCI)		1
Net OTTI losses recognized in income	(10)	(4)
Net realized gains (losses) excluding OTTI losses	270	(41)
Total net realized gains (losses)	260	(45)
Total revenues	4,185	3,808
Expenses
Losses and loss expenses	1,804	2,263
Policy benefits	147	91
Policy acquisition costs	582	559
Administrative expenses	510	499
Interest expense	62	63
Other (income) expense	(3)	(13)
Total expenses	3,102	3,462
Income before income tax	1,083	346
Income tax expense	110	96
Net income	973	250
Other comprehensive income
Unrealized appreciation	325	66
Reclassification adjustment for net realized gains included in net income	(33)	(56)
Subtotal	292	10
Change in:
Cumulative translation adjustment	88	232
Pension liability	(2)	(6)
Other comprehensive income, before income tax	378	236
Income tax expense related to OCI items	(80)	(48)
Other comprehensive income	298	188
Comprehensive income	$ 1,271	$ 438
Earnings per share
Basic earnings per share	$ 2.87	$ 0.74
Diluted earnings per share	$ 2.84	$ 0.73