Insurance Claim Reserves (Details) - Prior Year Reserve Development - Property-casualty [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Liability for claims and claim adjustment expense
Net favorable (unfavorable) prior year reserve development included in estimated claims and claim adjustment expenses incurred for claims arising in prior years			$ (62)	$ 383
Net favorable (unfavorable) prior year reserve development impacting the Company's results of operations			11	464
Accretion expense			34	35
Business Insurance [Member]
Liability for claims and claim adjustment expense
Net favorable (unfavorable) prior year reserve development impacting the Company's results of operations	$ (263)	$ (61)	(345)	254
Business Insurance [Member] | Asbestos reserves [Member]
Liability for claims and claim adjustment expense
Increase to reserves	284	212	284	212
Bond & Specialty Insurance [Member]
Liability for claims and claim adjustment expense
Net favorable (unfavorable) prior year reserve development impacting the Company's results of operations	72	63	249	171
Personal Insurance [Member]
Liability for claims and claim adjustment expense
Net favorable (unfavorable) prior year reserve development impacting the Company's results of operations	$ 37	$ 18	$ 107	$ 39