Segment information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Segment Reporting Information [Line Items]
Net premiums written	$ 10,302	$ 9,546	$ 19,501	$ 18,208
Net premiums earned	9,557	8,813	18,303	17,034
Losses and loss expenses	5,408	5,006	10,195	10,059
Policy benefits	159	185	304	352
Policy acquisition costs	1,739	1,698	3,476	3,363
Administrative expenses	818	775	1,596	1,519
Underwriting income (loss)	1,433	1,149	2,732	1,741
Net investment income (loss)	888	884	1,710	1,747
Other (income) expense	101	(777)	(209)	(1,267)
Amortization of purchased intangibles	71	73	142	145
Segment Income (loss)	2,149	2,737	4,509	4,610
Net realized gains (losses)	(504)	(33)	(403)	854
Interest expense	134	122	266	244
Cigna integration expenses	3	0	3	0
Income tax expense	293	317	648	655
Net income	1,215	2,265	3,189	4,565
Segment Reconciling Items
Segment Reporting Information [Line Items]
Net premiums written	0	0	0	0
Net premiums earned	0	0	0	0
Losses and loss expenses	9	3	10	2
Policy benefits	(18)	15	(49)	19
Policy acquisition costs	0	0	0	0
Administrative expenses	0	0	0	0
Underwriting income (loss)	9	(18)	39	(21)
Net investment income (loss)	(48)	(39)	(111)	(80)
Other (income) expense	(30)	(54)	(62)	(99)
Amortization of purchased intangibles	0	0	0	0
Segment Income (loss)	(9)	(3)	(10)	(2)
Net realized gains (losses)	9	3	10	2
Interest expense	0	0	0	0
Cigna integration expenses	0		0
Income tax expense	0	0	0	0
Net income	0	0	0	0
North America Commercial P&C Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	4,665	4,285	8,704	7,949
Net premiums earned	4,248	3,803	8,362	7,477
Losses and loss expenses	2,446	2,426	4,943	4,986
Policy benefits	0	0	0	0
Policy acquisition costs	545	489	1,118	1,003
Administrative expenses	277	245	542	499
Underwriting income (loss)	980	643	1,759	989
Net investment income (loss)	522	535	1,011	1,075
Other (income) expense	0	14	6	16
Amortization of purchased intangibles	0	0	0	0
Segment Income (loss)	1,502	1,164	2,764	2,048
North America Personal P&C Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	1,426	1,363	2,606	2,461
Net premiums earned	1,271	1,224	2,518	2,408
Losses and loss expenses	773	676	1,486	1,495
Policy benefits	0	0	0	0
Policy acquisition costs	258	245	518	492
Administrative expenses	73	67	142	127
Underwriting income (loss)	167	236	372	294
Net investment income (loss)	64	64	123	129
Other (income) expense	1	(5)	2	(4)
Amortization of purchased intangibles	3	3	5	6
Segment Income (loss)	227	302	488	421
North America Agricultural Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	738	512	800	695
Net premiums earned	573	410	544	520
Losses and loss expenses	478	331	386	416
Policy benefits	0	0	0	0
Policy acquisition costs	31	27	43	39
Administrative expenses	2	3	1	6
Underwriting income (loss)	62	49	114	59
Net investment income (loss)	7	8	14	15
Other (income) expense	0	0	0	0
Amortization of purchased intangibles	6	6	13	13
Segment Income (loss)	63	51	115	61
Overseas General Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	2,640	2,497	5,719	5,387
Net premiums earned	2,696	2,579	5,324	5,057
Losses and loss expenses	1,224	1,186	2,613	2,449
Policy benefits	0	0	0	0
Policy acquisition costs	697	699	1,376	1,367
Administrative expenses	278	279	547	545
Underwriting income (loss)	497	415	788	696
Net investment income (loss)	162	149	309	290
Other (income) expense	3	2	5	3
Amortization of purchased intangibles	14	13	28	25
Segment Income (loss)	642	549	1,064	958
Global Reinsurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	262	274	515	481
Net premiums earned	222	192	457	372
Losses and loss expenses	139	110	254	230
Policy benefits	0	0	0	0
Policy acquisition costs	57	47	119	92
Administrative expenses	10	10	19	18
Underwriting income (loss)	16	25	65	32
Net investment income (loss)	76	81	161	151
Other (income) expense	1	0	1	0
Amortization of purchased intangibles	0	0	0	0
Segment Income (loss)	91	106	225	183
Life Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	571	615	1,157	1,235
Net premiums earned	547	605	1,098	1,200
Losses and loss expenses	148	185	302	383
Policy benefits	177	170	353	333
Policy acquisition costs	151	191	302	370
Administrative expenses	88	83	172	165
Underwriting income (loss)	(17)	(24)	(31)	(51)
Net investment income (loss)	109	101	212	199
Other (income) expense	(12)	(26)	(40)	(60)
Amortization of purchased intangibles	3	1	5	2
Segment Income (loss)	101	102	216	206
Segment Corporate and Other
Segment Reporting Information [Line Items]
Net premiums written	0	0	0	0
Net premiums earned	0	0	0	0
Losses and loss expenses	191	89	201	98
Policy benefits	0	0	0	0
Policy acquisition costs	0	0	0	0
Administrative expenses	90	88	173	159
Underwriting income (loss)	(281)	(177)	(374)	(257)
Net investment income (loss)	(4)	(15)	(9)	(32)
Other (income) expense	138	(708)	(121)	(1,123)
Amortization of purchased intangibles	45	50	91	99
Segment Income (loss)	(468)	466	(353)	735
Net realized gains (losses)	(513)	(36)	(413)	852
Interest expense	134	122	266	244
Cigna integration expenses	3		3
Income tax expense	293	317	648	655
Net income	$ (1,411)	$ (9)	$ (1,683)	$ 688