Consolidated Statements Of Operations and Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Net premiums written	$ 29,244	$ 28,145	$ 17,713
(Increase) decrease in unearned premiums	(210)	604	(500)
Net premiums earned	29,034	28,749	17,213
Net investment income	3,125	2,865	2,194
Net realized gains (losses):
Other-than-temporary impairment (OTTI) losses gross	(46)	(111)	(151)
Portion of OTTI losses recognized in other comprehensive income (OCI)	1	8	39
Net OTTI losses recognized in income	(45)	(103)	(112)
Net realized gains (losses) excluding OTTI losses	129	(42)	(308)
Total Net realized gains (losses) including OTTI	84	(145)	(420)
Total revenues	32,243	31,469	18,987
Expenses
Losses and loss expenses	18,454	16,052	9,484
Policy benefits	676	588	543
Policy Acquisition Costs	5,781	5,904	2,941
Administrative expenses	2,833	3,081	2,270
Interest expense	607	605	300
Other (income) expense	(400)	(222)	(51)
Amortization of Purchased Intangibles	260	19	171
Chubb integration expenses	310	492	33
Total expenses	28,521	26,519	15,691
Income before income tax	3,722	4,950	3,296
Income tax expense	(139)	815	462
Net income	3,861	4,135	2,834
Other comprehensive income (loss)
Unrealized appreciation (depreciation)	618	(35)	(1,280)
Reclassification adjustment for net realized (gains) losses included in net income	15	119	151
Other comprehensive income (loss) after reclassification for net realized gains included in net income	633	84	(1,129)
Change in:
Cumulative foreign currency translation adjustment	471	(154)	(958)
Postretirement benefit liability adjustment	(16)	545	15
Other comprehensive income (loss), before income tax	1,088	475	(2,072)
Income tax (expense) benefit related to OCI items	(231)	(54)	146
Other comprehensive income (loss)	857	421	(1,926)
Comprehensive income	$ 4,718	$ 4,556	$ 908
Earnings per share
Basic earnings per share	$ 8.26	$ 8.94	$ 8.71
Diluted earnings per share	$ 8.19	$ 8.87	$ 8.62