Consolidated Statements Of Operations and Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues
Net premiums written	$ 9,078	$ 8,622	$ 25,410	$ 24,278
Increase in unearned premiums	(313)	(295)	(723)	(923)
Net premiums earned	8,765	8,327	24,687	23,355
Net investment income	840	873	2,528	2,568
Net realized gains (losses):
Other-than-temporary impairment (OTTI) losses gross	0	(54)	0	(81)
Portion of OTTI losses recognized in other comprehensive income (OCI)	0	30	0	31
Net OTTI losses recognized in income	0	(24)	0	(50)
Net realized gains (losses) excluding OTTI losses	(141)	(131)	(1,069)	(425)
Net gains (losses) recognized during the period	(141)	(155)	(1,069)	(475)
Total revenues	9,464	9,045	26,146	25,448
Expenses
Losses and loss expenses	5,835	5,052	16,897	13,865
Policy benefits	198	158	550	515
Policy acquisition costs	1,645	1,603	4,853	4,611
Administrative expenses	733	752	2,201	2,220
Interest expense	130	138	390	418
Other (income) expense	(485)	(57)	(372)	(326)
Amortization of purchased intangibles	72	76	217	229
Chubb integration expenses	0	2	0	9
Total expenses	8,128	7,724	24,736	21,541
Income before income tax	1,336	1,321	1,410	3,907
Income tax expense (includes $7, nil, $(35), and $(2) on reclassified unrealized gains and losses)	142	230	295	626
Net income	1,194	1,091	1,115	3,281
Other comprehensive income
Unrealized appreciation	687	694	1,456	3,791
Reclassification adjustment for net realized (gains) losses included in net income	(49)	11	303	43
Unrealized appreciation (Depreciation) after reclassification adjustment	638	705	1,759	3,834
Change in:
Cumulative foreign currency translation adjustment	246	(193)	(168)	(143)
Postretirement benefit liability adjustment	(23)	(17)	(59)	(62)
Other comprehensive income, before income tax	861	495	1,532	3,629
Income tax expense related to OCI items	(103)	(113)	(295)	(660)
Other comprehensive income	758	382	1,237	2,969
Comprehensive income	$ 1,952	$ 1,473	$ 2,352	$ 6,250
Earnings per share
Basic earnings per share	$ 2.64	$ 2.40	$ 2.47	$ 7.18
Diluted earnings per share	$ 2.63	$ 2.38	$ 2.46	$ 7.13
Total net realized gains (losses) reclassified from AOCI	$ 49	$ (11)	$ (303)	$ (43)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	7	0	(35)	(2)
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member]
Earnings per share
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	$ 7	$ 0	$ (35)	$ (2)