Segment Information (Details) - Assets by Segment - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Assets by segment
Total assets	$ 127,410	$ 125,978
Reportable Segments [Member]
Assets by segment
Total assets	126,532	125,115
Reportable Segments [Member] | Business Insurance [Member]
Assets by segment
Total assets	94,393	93,565
Reportable Segments [Member] | Bond & Specialty Insurance [Member]
Assets by segment
Total assets	12,136	11,478
Reportable Segments [Member] | Personal Insurance [Member]
Assets by segment
Total assets	20,003	20,072
Other assets [Member]
Assets by segment
Total assets	$ 878	$ 863