Segment Information (Details) - Assets by Segment - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Assets by segment
Total assets	$ 118,352	$ 115,717
Reportable Segments [Member]
Assets by segment
Total assets	117,521	114,916
Reportable Segments [Member] | Business Insurance [Member]
Assets by segment
Total assets	88,468	86,522
Reportable Segments [Member] | Bond & Specialty Insurance [Member]
Assets by segment
Total assets	10,539	10,119
Reportable Segments [Member] | Personal Insurance [Member]
Assets by segment
Total assets	18,514	18,275
Other assets [Member]
Assets by segment
Total assets	$ 831	$ 801