Segment information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Segment Reporting Information [Line Items]
Net premiums written	$ 11,951	$ 10,293	$ 22,661	$ 19,482
Net premiums earned	10,999	9,549	21,141	18,286
Losses and loss expenses	5,683	5,206	10,831	9,770
Policy benefits (includes remeasurement losses of $5, nil, $4, and $6)	830	361	1,627	734
Policy acquisition costs	2,016	1,726	3,964	3,445
Administrative expenses	969	818	1,899	1,596
Underwriting income (loss)	1,501	1,438	2,820	2,741
Net investment income (loss)	1,145	888	2,252	1,710
Other (income) expense	(100)	101	(396)	(211)
Amortization of purchased intangibles	70	71	142	142
Segment Income (loss)	2,676	2,154	5,326	4,520
Net realized gains (losses)	(304)	(503)	(381)	(480)
Market risk benefits gains (losses)	(7)	(33)	(122)	16
Interest Income (Expense), Net	165	134	325	266
Cigna integration expenses	15	3	37	3
Income tax expense	392	291	776	644
Net income	1,793	1,190	3,685	3,143
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	5	9	4	10
Policy benefits (includes remeasurement losses of $5, nil, $4, and $6)	(12)	(18)	(37)	(49)
Policy acquisition costs	0	0	0	0
Administrative expenses	0	0	0	0
Underwriting income (loss)	7	9	33	39
Net investment income (loss)	(93)	(48)	(184)	(111)
Other (income) expense	(81)	(30)	(147)	(62)
Amortization of purchased intangibles	0	0	0	0
Segment Income (loss)	(5)	(9)	(4)	(10)
Net realized gains (losses)	5	9	4	10
Market risk benefits gains (losses)	0	0	0	0
Interest Income (Expense), Net	0	0	0	0
Cigna integration expenses	0	0	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		8,704
Net premiums earned		4,248		8,362
Losses and loss expenses		2,446		4,943
Policy benefits (includes remeasurement losses of $5, nil, $4, and $6)		0		0
Policy acquisition costs		545		1,118
Administrative expenses		277		542
Underwriting income (loss)		980		1,759
Net investment income (loss)		522		1,011
Other (income) expense		0		6
Amortization of purchased intangibles		0		0
Segment Income (loss)		1,502		2,764
North America Personal P&C Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums written		1,426		2,606
Net premiums earned		1,271		2,518
Losses and loss expenses		773		1,486
Policy benefits (includes remeasurement losses of $5, nil, $4, and $6)		0		0
Policy acquisition costs		258		518
Administrative expenses		73		142
Underwriting income (loss)		167		372
Net investment income (loss)		64		123
Other (income) expense		1		2
Amortization of purchased intangibles		3		5
Segment Income (loss)		227		488
North America Agricultural Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	767	738	1,060	800
Net premiums earned	635	573	794	544
Losses and loss expenses	507	478	647	386
Policy benefits (includes remeasurement losses of $5, nil, $4, and $6)	0	0	0	0
Policy acquisition costs	37	31	52	43
Administrative expenses	3	2	6	1
Underwriting income (loss)	88	62	89	114
Net investment income (loss)	14	7	31	14
Other (income) expense	(1)	0	0	0
Amortization of purchased intangibles	7	6	13	13
Segment Income (loss)	96	63	107	115
Overseas General Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	2,885	2,640	6,148	5,719
Net premiums earned	2,908	2,696	5,694	5,324
Losses and loss expenses	1,267	1,143	2,504	2,439
Policy benefits (includes remeasurement losses of $5, nil, $4, and $6)	137	81	247	174
Policy acquisition costs	746	697	1,459	1,376
Administrative expenses	292	278	572	547
Underwriting income (loss)	466	497	912	788
Net investment income (loss)	200	162	388	309
Other (income) expense	(10)	3	(19)	5
Amortization of purchased intangibles	15	14	33	28
Segment Income (loss)	661	642	1,286	1,064
Global Reinsurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	293	262	570	515
Net premiums earned	237	222	481	457
Losses and loss expenses	91	139	203	254
Policy benefits (includes remeasurement losses of $5, nil, $4, and $6)	0	0	0	0
Policy acquisition costs	65	57	127	119
Administrative expenses	9	10	18	19
Underwriting income (loss)	72	16	133	65
Net investment income (loss)	48	76	97	161
Other (income) expense	0	1	(1)	1
Amortization of purchased intangibles	0	0	0	0
Segment Income (loss)	120	91	231	225
Life Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	1,270	562	2,563	1,138
Net premiums earned	1,256	539	2,520	1,081
Losses and loss expenses	35	27	67	51
Policy benefits (includes remeasurement losses of $5, nil, $4, and $6)	705	298	1,417	609
Policy acquisition costs	277	138	550	271
Administrative expenses	170	88	337	172
Underwriting income (loss)	69	(12)	149	(22)
Net investment income (loss)	161	109	314	212
Other (income) expense	(26)	(12)	(41)	(42)
Amortization of purchased intangibles	2	3	6	5
Segment Income (loss)	254	106	498	227
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	61	191	72	201
Policy benefits (includes remeasurement losses of $5, nil, $4, and $6)	0	0	0	0
Policy acquisition costs	0	0	0	0
Administrative expenses	95	90	192	173
Underwriting income (loss)	(156)	(281)	(264)	(374)
Net investment income (loss)	3	(4)	14	(9)
Other (income) expense	14	138	(200)	(121)
Amortization of purchased intangibles	43	45	85	91
Segment Income (loss)	(210)	(468)	(135)	(353)
Net realized gains (losses)	(309)	(512)	(385)	(490)
Market risk benefits gains (losses)	(7)	(33)	(122)	16
Interest Income (Expense), Net	165	134	325	266
Cigna integration expenses	15	3	37	3
Income tax expense	392	291	776	644
Net income	(1,098)	$ (1,441)	(1,780)	$ (1,740)
North America Commercial P&C Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	5,155		9,443
Net premiums earned	4,606		8,975
Losses and loss expenses	2,871		5,600
Policy benefits (includes remeasurement losses of $5, nil, $4, and $6)	0		0
Policy acquisition costs	614		1,227
Administrative expenses	316		611
Underwriting income (loss)	805		1,537
Net investment income (loss)	726		1,424
Other (income) expense	5		12
Amortization of purchased intangibles	0		0
Segment Income (loss)	1,526		2,949
Segment Insurance North American Personal P&C
Segment Reporting Information [Line Items]
Net premiums written	1,581		2,877
Net premiums earned	1,357		2,677
Losses and loss expenses	846		1,734
Policy benefits (includes remeasurement losses of $5, nil, $4, and $6)	0		0
Policy acquisition costs	277		549
Administrative expenses	84		163
Underwriting income (loss)	150		231
Net investment income (loss)	86		168
Other (income) expense	(1)		0
Amortization of purchased intangibles	3		5
Segment Income (loss)	$ 234		$ 394