Segment Information (Details) - Assets by Segment - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Assets by segment
Total assets	$ 120,466	$ 116,764
Reportable segments [Member]
Assets by segment
Total assets	119,482	116,170
Reportable segments [Member] | Business Insurance [Member]
Assets by segment
Total assets	90,353	88,422
Reportable segments [Member] | Bond & Specialty Insurance [Member]
Assets by segment
Total assets	10,146	9,420
Reportable segments [Member] | Personal Insurance [Member]
Assets by segment
Total assets	18,983	18,328
Other assets [Member]
Assets by segment
Total assets	$ 984	$ 594