Segment Information (Details) - Assets by Segment - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Assets by segment
Total assets	$ 121,384	$ 115,717
Reportable Segments [Member]
Assets by segment
Total assets	120,522	114,916
Reportable Segments [Member] | Business Insurance [Member]
Assets by segment
Total assets	89,980	86,522
Reportable Segments [Member] | Bond & Specialty Insurance [Member]
Assets by segment
Total assets	11,088	10,119
Reportable Segments [Member] | Personal Insurance [Member]
Assets by segment
Total assets	19,454	18,275
Other assets [Member]
Assets by segment
Total assets	$ 862	$ 801