Consolidated Statements Of Operations and Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues
Net premiums written	$ 33,820	$ 32,275	$ 30,579
Increase in unearned premiums	(703)	(985)	(515)
Net premiums earned	33,117	31,290	30,064
Net investment income	3,375	3,426	3,305
Realized Investment Gains (Losses)	(498)	(530)	(652)
Net realized gains (losses):
Other-than-temporary impairment (OTTI) losses gross		(90)	(52)
Portion of OTTI losses recognized in other comprehensive income (OCI)	0	32	3
Net OTTI losses recognized in income		(58)	(49)
Net realized, Gain (Loss), Excluding Other-than-temporary Impairment Loss	(498)	(472)	(603)
Total revenues	35,994	34,186	32,717
Expenses
Losses and loss expenses	21,710	18,730	18,067
Policy benefits	784	740	590
Policy Acquisition Costs	6,547	6,153	5,912
Administrative expenses	2,979	3,030	2,886
Interest expense	516	552	641
Other (income) expense	(994)	(596)	(434)
Amortization of Purchased Intangibles	290	305	339
Chubb integration expenses	0	23	59
Total expenses	31,832	28,937	28,060
Income before income tax	4,162	5,249	4,657
Income tax expense (includes benefit of $(36), nil, and $(41) on unrealized gains and losses reclassified from AOCI)	629	795	695
Net income	3,533	4,454	3,962
Other comprehensive income (loss)
Unrealized appreciation (depreciation)	2,311	3,704	(2,298)
Reclassification adjustment for net realized (gains) losses included in net income	281	31	302
Other comprehensive income (loss) after reclassification for net realized gains included in net income	2,592	3,735	(1,996)
Change in:
Cumulative foreign currency translation adjustment	306	13	(802)
Postretirement benefit liability adjustment	(232)	(76)	(321)
Other comprehensive income (loss), before income tax	2,666	3,672	(3,119)
Income tax (expense) benefit related to OCI items	(416)	(605)	399
Other comprehensive income (loss)	2,250	3,067	(2,720)
Comprehensive income	$ 5,783	$ 7,521	$ 1,242
Earnings per share
Basic earnings per share	$ 7.82	$ 9.77	$ 8.55
Diluted earnings per share	$ 7.79	$ 9.71	$ 8.49