Segment Information (Details) - Assets by Segment - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Assets by segment
Total assets	$ 142,309	$ 143,708
Reportable Segments [Member]
Assets by segment
Total assets	141,156	142,547
Reportable Segments [Member] \| Business Insurance [Member]
Assets by segment
Total assets	106,397	106,084
Reportable Segments [Member] \| Bond & Specialty Insurance [Member]
Assets by segment
Total assets	13,790	13,676
Reportable Segments [Member] \| Personal Insurance [Member]
Assets by segment
Total assets	20,969	22,787
Other assets [Member]
Assets by segment
Total assets	$ 1,153	$ 1,161

Amount of asset recognized for present right to economic benefit.

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+ Details