Unpaid losses and loss expenses (A&E Loss Roll-forward) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Liability For Asbestos And Environmental Claims Net Roll Forward
Balance (gross) at beginning of year		$ 1,868	$ 1,988	$ 2,117
Balance (net) at beginning of year		1,252	1,326	1,447
Incurred activity, gross		148	229	175
Incurred activity, net	[1]	104	131	98
Paid activity, gross		(388)	(349)	(304)
Paid activity, net		(254)	(205)	(219)
Balance (gross) at end of year		1,628	1,868	1,988
Balance (net) at end of year		1,102	1,252	1,326
Asbestos Issue [Member]
Liability For Asbestos And Environmental Claims Net Roll Forward
Balance (gross) at beginning of year		1,351	1,459	1,492
Balance (net) at beginning of year		873	916	964
Incurred activity, gross		96	150	129
Incurred activity, net		64	90	70
Paid activity, gross		(221)	(258)	(162)
Paid activity, net		(137)	(133)	(118)
Balance (gross) at end of year		1,226	1,351	1,459
Balance (net) at end of year		800	873	916
Environmental Issue [Member]
Liability For Asbestos And Environmental Claims Net Roll Forward
Balance (gross) at beginning of year		517	529	625
Balance (net) at beginning of year		379	410	483
Incurred activity, gross		52	79	46
Incurred activity, net		40	41	28
Paid activity, gross		(167)	(91)	(142)
Paid activity, net		(117)	(72)	(101)
Balance (gross) at end of year		402	517	529
Balance (net) at end of year		302	379	$ 410
Brandywine [Member]
Liability For Asbestos And Environmental Claims Net Roll Forward
Balance (net) at beginning of year		736
Balance (net) at end of year		646	736
Westchester Specialty [Member]
Liability For Asbestos And Environmental Claims Net Roll Forward
Balance (net) at beginning of year		103
Balance (net) at end of year		100	103
Other Segments [Member]
Liability For Asbestos And Environmental Claims Net Roll Forward
Balance (net) at beginning of year		80
Balance (net) at end of year		70	80
The Chubb Corporation [Member]
Liability For Asbestos And Environmental Claims Net Roll Forward
Balance (net) at beginning of year		333
Balance (net) at end of year		$ 286	$ 333

[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)