Segment Information (Details) - Assets by Segment - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Assets by segment
Total assets	$ 114,317	$ 120,466
Reportable Segments [Member]
Assets by segment
Total assets	113,346	119,482
Reportable Segments [Member] | Business Insurance [Member]
Assets by segment
Total assets	85,149	90,353
Reportable Segments [Member] | Bond & Specialty Insurance [Member]
Assets by segment
Total assets	10,128	10,146
Reportable Segments [Member] | Personal Insurance [Member]
Assets by segment
Total assets	18,069	18,983
Other assets [Member]
Assets by segment
Total assets	$ 971	$ 984