Segment information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Segment Reporting Information [Line Items]
Net premiums written	$ 12,020	$ 10,510	$ 31,521	$ 28,718
Net premiums earned	11,535	10,000	29,838	27,034
Losses and loss expenses	7,279	6,629	17,474	16,688
Policy benefits	486	151	790	503
Policy acquisition costs	1,975	1,778	5,451	5,141
Administrative expenses	883	806	2,479	2,325
Underwriting income (loss)	912	636	3,644	2,377
Net investment income (loss)	979	866	2,689	2,613
Other (income) expense	188	(763)	(21)	(2,030)
Amortization of purchased intangibles	69	71	211	216
Segment Income (loss)	1,634	2,194	6,143	6,804
Net realized gains (losses)	(384)	(21)	(787)	833
Interest expense	150	122	416	366
Cigna integration expenses	23	0	26	0
Income tax expense	265	218	913	873
Net income	812	1,833	4,001	6,398
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	(19)	(10)	(9)	(8)
Policy benefits	(67)	(24)	(116)	(5)
Policy acquisition costs	0	0	0	0
Administrative expenses	0	0	0	0
Underwriting income (loss)	86	34	125	13
Net investment income (loss)	(69)	(55)	(180)	(135)
Other (income) expense	(2)	(31)	(64)	(130)
Amortization of purchased intangibles	0	0	0	0
Segment Income (loss)	19	10	9	8
Net realized gains (losses)	(19)	(10)	(9)	(8)
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	4,722	4,369	13,426	12,318
Net premiums earned	4,283	3,954	12,645	11,431
Losses and loss expenses	3,036	2,754	7,979	7,740
Policy benefits	0	0	0	0
Policy acquisition costs	583	537	1,701	1,540
Administrative expenses	272	273	814	772
Underwriting income (loss)	392	390	2,151	1,379
Net investment income (loss)	589	507	1,600	1,582
Other (income) expense	6	8	12	24
Amortization of purchased intangibles	0	0	0	0
Segment Income (loss)	975	889	3,739	2,937
North America Personal P&C Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	1,392	1,300	3,998	3,761
Net premiums earned	1,334	1,244	3,852	3,652
Losses and loss expenses	857	846	2,343	2,341
Policy benefits	0	0	0	0
Policy acquisition costs	274	254	792	746
Administrative expenses	71	73	213	200
Underwriting income (loss)	132	71	504	365
Net investment income (loss)	76	60	199	189
Other (income) expense	1	1	3	(3)
Amortization of purchased intangibles	2	2	7	8
Segment Income (loss)	205	128	693	549
North America Agricultural Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	1,723	1,415	2,523	2,110
Net premiums earned	1,673	1,338	2,217	1,858
Losses and loss expenses	1,444	1,138	1,830	1,554
Policy benefits	0	0	0	0
Policy acquisition costs	68	61	111	100
Administrative expenses	3	4	4	10
Underwriting income (loss)	158	135	272	194
Net investment income (loss)	9	6	23	21
Other (income) expense	1	0	1	0
Amortization of purchased intangibles	7	7	20	20
Segment Income (loss)	159	134	274	195
Overseas General Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	2,645	2,596	8,364	7,983
Net premiums earned	2,741	2,664	8,065	7,721
Losses and loss expenses	1,441	1,487	4,054	3,936
Policy benefits	0	0	0	0
Policy acquisition costs	720	703	2,096	2,070
Administrative expenses	264	266	811	811
Underwriting income (loss)	316	208	1,104	904
Net investment income (loss)	151	157	460	447
Other (income) expense	(2)	0	3	3
Amortization of purchased intangibles	12	11	40	36
Segment Income (loss)	457	354	1,521	1,312
Global Reinsurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	265	221	780	702
Net premiums earned	255	211	712	583
Losses and loss expenses	311	192	565	422
Policy benefits	0	0	0	0
Policy acquisition costs	59	55	178	147
Administrative expenses	8	9	27	27
Underwriting income (loss)	(123)	(45)	(58)	(13)
Net investment income (loss)	71	99	232	250
Other (income) expense	0	0	1	0
Amortization of purchased intangibles	0	0	0	0
Segment Income (loss)	(52)	54	173	237
Life Insurance [Member]
Segment Reporting Information [Line Items]
Net premiums written	1,273	609	2,430	1,844
Net premiums earned	1,249	589	2,347	1,789
Losses and loss expenses	135	179	437	562
Policy benefits	553	175	906	508
Policy acquisition costs	271	168	573	538
Administrative expenses	174	82	346	247
Underwriting income (loss)	116	(15)	85	(66)
Net investment income (loss)	147	102	359	301
Other (income) expense	(10)	(19)	(50)	(79)
Amortization of purchased intangibles	2	2	7	4
Segment Income (loss)	271	104	487	310
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	74	43	275	141
Policy benefits	0	0	0	0
Policy acquisition costs	0	0	0	0
Administrative expenses	91	99	264	258
Underwriting income (loss)	(165)	(142)	(539)	(399)
Net investment income (loss)	5	(10)	(4)	(42)
Other (income) expense	194	(722)	73	(1,845)
Amortization of purchased intangibles	46	49	137	148
Segment Income (loss)	(400)	521	(753)	1,256
Net realized gains (losses)	(365)	(11)	(778)	841
Interest expense	150	122	416	366
Cigna integration expenses	23		26
Income tax expense	265	218	913	873
Net income	$ (1,203)	$ 170	$ (2,886)	$ 858