Unpaid losses and loss expenses (A&E Loss Roll-forward) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Liability For Asbestos And Environmental Claims Net Roll Forward
Balance (gross) at beginning of year		$ 1,628	$ 1,868	$ 1,988
Balance (net) at beginning of year		1,102	1,252	1,326
Incurred activity, gross		212	148	229
Incurred activity, net	[1]	132	104	131
Paid activity, gross		(330)	(388)	(349)
Paid activity, net		(221)	(254)	(205)
Balance (gross) at end of year		1,510	1,628	1,868
Balance (net) at end of year		1,013	1,102	1,252
Asbestos Issue [Member]
Liability For Asbestos And Environmental Claims Net Roll Forward
Balance (gross) at beginning of year		1,226	1,351	1,459
Balance (net) at beginning of year		800	873	916
Incurred activity, gross		87	96	150
Incurred activity, net		55	64	90
Paid activity, gross		(215)	(221)	(258)
Paid activity, net		(152)	(137)	(133)
Balance (gross) at end of year		1,098	1,226	1,351
Balance (net) at end of year		703	800	873
Environmental Issue [Member]
Liability For Asbestos And Environmental Claims Net Roll Forward
Balance (gross) at beginning of year		402	517	529
Balance (net) at beginning of year		302	379	410
Incurred activity, gross		125	52	79
Incurred activity, net		77	40	41
Paid activity, gross		(115)	(167)	(91)
Paid activity, net		(69)	(117)	(72)
Balance (gross) at end of year		412	402	517
Balance (net) at end of year		310	302	$ 379
Brandywine [Member]
Liability For Asbestos And Environmental Claims Net Roll Forward
Balance (net) at beginning of year		646
Balance (net) at end of year		602	646
Westchester Specialty [Member]
Liability For Asbestos And Environmental Claims Net Roll Forward
Balance (net) at beginning of year		100
Balance (net) at end of year		98	100
Other Segments [Member]
Liability For Asbestos And Environmental Claims Net Roll Forward
Balance (net) at beginning of year		70
Balance (net) at end of year		47	70
The Chubb Corporation [Member]
Liability For Asbestos And Environmental Claims Net Roll Forward
Balance (net) at beginning of year		286
Balance (net) at end of year		$ 266	$ 286

[1] Excludes unallocated loss expenses and the net activity reflects third-party reinsurance other than the aggregate excess of loss reinsurance provided by National Indemnity Company (NICO) to Westchester Specialty (see Westchester Specialty section below)