Segment Information (Details) - Assets by Segment - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Assets by segment
Total assets	$ 133,189	$ 125,978
Reportable segments [Member]
Assets by segment
Total assets	132,077	125,115
Reportable segments [Member] | Business Insurance [Member]
Assets by segment
Total assets	98,311	93,565
Reportable segments [Member] | Bond & Specialty Insurance [Member]
Assets by segment
Total assets	12,628	11,478
Reportable segments [Member] | Personal Insurance [Member]
Assets by segment
Total assets	21,138	20,072
Other assets [Member]
Assets by segment
Total assets	$ 1,112	$ 863