Segment Information (Operations By Segment) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Net premiums written	$ 41,755	$ 37,868	$ 33,820
Net premiums earned	40,389	36,355	33,117
Losses and loss expenses	23,342	21,980	21,710
Policy benefits	1,492	699	784
Policy acquisition costs	7,392	6,918	6,547
Administrative expenses	3,395	3,136	2,979
Underwriting Income (Loss)	4,768	3,622	1,097
Net investment income	3,742	3,456	3,375
Other (income) expense	74	(2,365)	(994)
Amortization of purchased intangibles	285	287	290
Segment income (loss)	8,151	9,156	5,176
Net realized gains (losses)	(965)	1,152	(498)
Interest expense	570	492	516
Income tax expense	1,255	1,277	629
Cigna integration expenses	48	0	0
Net income	5,313	8,539	3,533
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Net premiums written	0	0	0
Net premiums earned	0	0	0
Losses and loss expenses	(11)	(8)	1
Policy benefits	(42)	(8)	58
Policy acquisition costs	0	0	0
Administrative expenses	0	0	0
Underwriting Income (Loss)	53	16	(59)
Net investment income	(240)	(179)	(115)
Other (income) expense	(198)	(171)	(173)
Amortization of purchased intangibles	0	0	0
Segment income (loss)	11	8	(1)
Net realized gains (losses)	(11)	(8)	1
Interest expense	0	0	0
Income tax expense	0	0	0
Cigna integration expenses	0
Net income	0	0	0
North America Commercial P&C Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	17,889	16,415	14,474
Net premiums earned	17,107	15,461	13,964
Losses and loss expenses	10,828	10,015	10,129
Policy benefits	0	0	0
Policy acquisition costs	2,313	2,082	1,942
Administrative expenses	1,113	1,052	1,006
Underwriting Income (Loss)	2,853	2,312	887
Net investment income	2,247	2,078	2,061
Other (income) expense	17	31	23
Amortization of purchased intangibles	0	0	0
Segment income (loss)	5,083	4,359	2,925
North America Personal P&C Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	5,313	5,002	4,920
Net premiums earned	5,180	4,915	4,866
Losses and loss expenses	3,186	2,924	3,187
Policy benefits	0	0	0
Policy acquisition costs	1,057	1,001	974
Administrative expenses	291	276	270
Underwriting Income (Loss)	646	714	435
Net investment income	283	249	260
Other (income) expense	4	(2)	5
Amortization of purchased intangibles	10	10	11
Segment income (loss)	915	955	679
North America Agricultural Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	2,907	2,388	1,846
Net premiums earned	2,838	2,338	1,822
Losses and loss expenses	2,557	1,962	1,544
Policy benefits	0	0	0
Policy acquisition costs	126	124	123
Administrative expenses	(10)	(3)	9
Underwriting Income (Loss)	165	255	146
Net investment income	36	28	30
Other (income) expense	1	1	1
Amortization of purchased intangibles	26	26	27
Segment income (loss)	174	256	148
Overseas General Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	11,060	10,713	9,335
Net premiums earned	10,803	10,441	9,285
Losses and loss expenses	5,252	5,143	5,255
Policy benefits	0	0	0
Policy acquisition costs	2,818	2,799	2,568
Administrative expenses	1,070	1,078	1,034
Underwriting Income (Loss)	1,663	1,421	428
Net investment income	626	597	534
Other (income) expense	2	0	13
Amortization of purchased intangibles	57	48	45
Segment income (loss)	2,230	1,970	904
Global Reinsurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	943	873	731
Net premiums earned	922	798	698
Losses and loss expenses	670	632	435
Policy benefits	0	0	0
Policy acquisition costs	240	200	174
Administrative expenses	36	35	37
Underwriting Income (Loss)	(24)	(69)	52
Net investment income	281	331	307
Other (income) expense	1	0	2
Amortization of purchased intangibles	0	0	0
Segment income (loss)	256	262	357
Life Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	3,643	2,477	2,514
Net premiums earned	3,539	2,402	2,482
Losses and loss expenses	497	740	724
Policy benefits	1,534	707	726
Policy acquisition costs	838	712	766
Administrative expenses	510	333	320
Underwriting Income (Loss)	160	(90)	(54)
Net investment income	509	407	385
Other (income) expense	(45)	(106)	(74)
Amortization of purchased intangibles	10	5	4
Segment income (loss)	704	418	401
Corporate and Other
Segment Reporting Information [Line Items]
Net premiums written	0	0	0
Net premiums earned	0	0	0
Losses and loss expenses	363	572	435
Policy benefits	0	0	0
Policy acquisition costs	0	0	0
Administrative expenses	385	365	303
Underwriting Income (Loss)	(748)	(937)	(738)
Net investment income	0	(55)	(87)
Other (income) expense	292	(2,118)	(791)
Amortization of purchased intangibles	182	198	203
Segment income (loss)	(1,222)	928	(237)
Net realized gains (losses)	(954)	1,160	(499)
Interest expense	570	492	516
Income tax expense	1,255	1,277	629
Cigna integration expenses	48
Net income	$ (4,049)	$ 319	$ (1,881)