Segment information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Segment Reporting Information [Line Items]
Net premiums written	$ 13,360	$ 11,951	$ 25,581	$ 22,661
Net premiums earned	12,292	10,999	23,875	21,141
Losses and loss expenses	6,431	5,683	12,158	10,831
Policy benefits (includes remeasurement losses of $3, $5, $22 and $4)	1,219	830	2,399	1,627
Policy acquisition costs	2,226	2,016	4,433	3,964
Administrative expenses	1,094	969	2,164	1,899
Underwriting income (loss)	1,322	1,501	2,721	2,820
Net investment income (loss)	1,468	1,145	2,859	2,252
Other (income) expense	(110)	(100)	(301)	(396)
Amortization of purchased intangibles	80	70	160	142
Segment Income (loss)	2,820	2,676	5,721	5,326
Net realized gains (losses)	104	(304)	3	(381)
Market risk benefits gains (losses)	(29)	(7)	(8)	(122)
Interest Income (Expense), Net	182	165	360	325
Cigna integration expenses	7	15	14	37
Income tax expense	490	392	832	776
Net Income	2,216	1,793	4,510	3,685
Net income (loss) attributable to noncontrolling interests	(14)	0	137	0
Net income (loss)	2,230	1,793	4,373	3,685
North America Commercial P&C Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	5,501	5,155	10,190	9,443
Net premiums earned	4,900	4,606	9,780	8,975
Losses and loss expenses	3,074	2,871	6,249	5,600
Policy benefits (includes remeasurement losses of $3, $5, $22 and $4)	0	0	0	0
Policy acquisition costs	660	614	1,348	1,227
Administrative expenses	327	316	655	611
Underwriting income (loss)	839	805	1,528	1,537
Net investment income (loss)	863	726	1,689	1,424
Other (income) expense	15	5	22	12
Amortization of purchased intangibles	0	0	0	0
Segment Income (loss)	1,687	1,526	3,195	2,949
North American Personal P&C Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	1,776	1,581	3,232	2,877
Net premiums earned	1,512	1,357	2,983	2,677
Losses and loss expenses	876	846	1,775	1,734
Policy benefits (includes remeasurement losses of $3, $5, $22 and $4)	0	0	0	0
Policy acquisition costs	299	277	599	549
Administrative expenses	88	84	174	163
Underwriting income (loss)	249	150	435	231
Net investment income (loss)	108	86	210	168
Other (income) expense	(2)	(1)	(1)	0
Amortization of purchased intangibles	2	3	4	5
Segment Income (loss)	357	234	642	394
North America Agricultural Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	758	767	1,007	1,060
Net premiums earned	626	635	754	794
Losses and loss expenses	543	507	592	647
Policy benefits (includes remeasurement losses of $3, $5, $22 and $4)	0	0	0	0
Policy acquisition costs	45	37	66	52
Administrative expenses	3	3	5	6
Underwriting income (loss)	35	88	91	89
Net investment income (loss)	21	14	42	31
Other (income) expense	0	(1)	0	0
Amortization of purchased intangibles	7	7	13	13
Segment Income (loss)	49	96	120	107
Overseas General Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	3,334	2,885	7,169	6,148
Net premiums earned	3,347	2,908	6,545	5,694
Losses and loss expenses	1,671	1,267	3,097	2,504
Policy benefits (includes remeasurement losses of $3, $5, $22 and $4)	92	137	192	247
Policy acquisition costs	842	746	1,665	1,459
Administrative expenses	348	292	679	572
Underwriting income (loss)	394	466	912	912
Net investment income (loss)	283	200	550	388
Other (income) expense	4	(10)	9	(19)
Amortization of purchased intangibles	20	15	40	33
Segment Income (loss)	653	661	1,413	1,286
Global Reinsurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	411	293	770	570
Net premiums earned	339	237	634	481
Losses and loss expenses	155	91	292	203
Policy benefits (includes remeasurement losses of $3, $5, $22 and $4)	0	0	0	0
Policy acquisition costs	80	65	161	127
Administrative expenses	11	9	20	18
Underwriting income (loss)	93	72	161	133
Net investment income (loss)	58	48	115	97
Other (income) expense	0	0	0	(1)
Amortization of purchased intangibles	0	0	0	0
Segment Income (loss)	151	120	276	231
Life Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	1,580	1,270	3,213	2,563
Net premiums earned	1,568	1,256	3,179	2,520
Losses and loss expenses	22	35	54	67
Policy benefits (includes remeasurement losses of $3, $5, $22 and $4)	1,031	705	2,101	1,417
Policy acquisition costs	300	277	594	550
Administrative expenses	218	170	425	337
Underwriting income (loss)	(3)	69	5	149
Net investment income (loss)	258	161	488	314
Other (income) expense	(32)	(26)	(72)	(41)
Amortization of purchased intangibles	11	2	21	6
Segment Income (loss)	276	254	544	498
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	93	61	103	72
Policy benefits (includes remeasurement losses of $3, $5, $22 and $4)	0	0	0	0
Policy acquisition costs	0	0	0	0
Administrative expenses	99	95	206	192
Underwriting income (loss)	(192)	(156)	(309)	(264)
Net investment income (loss)	(32)	3	(58)	14
Other (income) expense	7	14	(61)	(200)
Amortization of purchased intangibles	40	43	82	85
Segment Income (loss)	(271)	(210)	(388)	(135)
Net realized gains (losses)	22	(309)	(78)	(385)
Market risk benefits gains (losses)	(29)	(7)	(8)	(122)
Interest Income (Expense), Net	182	165	360	325
Cigna integration expenses	7	15	14	37
Income tax expense	490	392	832	776
Net Income	(957)	(1,098)	(1,680)	(1,780)
Net income (loss) attributable to noncontrolling interests	(14)		137
Net income (loss)	(943)		(1,817)
Segment Measure 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	(3)	5	(4)	4
Policy benefits (includes remeasurement losses of $3, $5, $22 and $4)	96	(12)	106	(37)
Policy acquisition costs	0	0	0	0
Administrative expenses		0	0	0
Underwriting income (loss)	(93)	7	(102)	33
Net investment income (loss)	(91)	(93)	(177)	(184)
Other (income) expense	(102)	(81)	(198)	(147)
Amortization of purchased intangibles	0	0	0	0
Segment Income (loss)	(82)	(5)	(81)	(4)
Net realized gains (losses)	82	5	81	4
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
Net income (loss) attributable to noncontrolling interests	0		0
Net income (loss)	$ 0		$ 0