Segment Information (Details) - Assets by Segment - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Assets by segment
Total assets	$ 118,592	$ 120,466
Reportable Segments [Member]
Assets by segment
Total assets	117,734	119,482
Reportable Segments [Member] | Business Insurance [Member]
Assets by segment
Total assets	89,036	90,353
Reportable Segments [Member] | Bond & Specialty Insurance [Member]
Assets by segment
Total assets	10,171	10,146
Reportable Segments [Member] | Personal Insurance [Member]
Assets by segment
Total assets	18,527	18,983
Other assets [Member]
Assets by segment
Total assets	$ 858	$ 984