Consolidated Statements Of Operations and Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues
Net premiums written	$ 32,275	$ 30,579	$ 29,244
Increase in unearned premiums	(985)	(515)	(210)
Net premiums earned	31,290	30,064	29,034
Net investment income	3,426	3,305	3,125
Net realized gains (losses):
Other-than-temporary impairment (OTTI) losses gross	(90)	(52)	(46)
Portion of OTTI losses recognized in other comprehensive income (OCI)	32	3	1
Net OTTI losses recognized in income	(58)	(49)	(45)
Net realized, Gain (Loss), Excluding Other-than-temporary Impairment Loss	(472)	(603)	129
Total net realized gains (losses) (includes $(31), $(302), and $(15) reclassified from AOCI)	(530)	(652)	84
Total revenues	34,186	32,717	32,243
Expenses
Losses and loss expenses	18,730	18,067	18,454
Policy benefits	740	590	676
Policy Acquisition Costs	6,153	5,912	5,781
Administrative expenses	3,030	2,886	2,833
Interest expense	552	641	607
Other (income) expense	(596)	(434)	(400)
Amortization of Purchased Intangibles	305	339	260
Chubb integration expenses	23	59	310
Total expenses	28,937	28,060	28,521
Income before income tax	5,249	4,657	3,722
Income tax expense (benefit) (includes nil, $(41), and $(13) on reclassified unrealized gains and losses)	795	695	(139)
Net income	4,454	3,962	3,861
Other comprehensive income (loss)
Unrealized appreciation (depreciation)	3,704	(2,298)	618
Reclassification adjustment for net realized (gains) losses included in net income	31	302	15
Other comprehensive income (loss) after reclassification for net realized gains included in net income	3,735	(1,996)	633
Change in:
Cumulative foreign currency translation adjustment	13	(802)	471
Postretirement benefit liability adjustment	(76)	(321)	(16)
Other comprehensive income (loss), before income tax	3,672	(3,119)	1,088
Income tax (expense) benefit related to OCI items	(605)	399	(231)
Other comprehensive income (loss)	3,067	(2,720)	857
Comprehensive income	$ 7,521	$ 1,242	$ 4,718
Earnings per share
Basic earnings per share	$ 9.77	$ 8.55	$ 8.26
Diluted earnings per share	$ 9.71	$ 8.49	$ 8.19