Segment Information (Details) - Assets by Segment - USD ($) $ in Millions	Sep. 30, 2026	Dec. 31, 2025
Segment reporting information
Total assets	$ 142,089	$ 143,708
Reportable Segments [Member]
Segment reporting information
Total assets	140,906	142,547
Reportable Segments [Member] \| Business Insurance [Member]
Segment reporting information
Total assets	105,291	106,084
Reportable Segments [Member] \| Bond & Specialty Insurance [Member]
Segment reporting information
Total assets	14,523	13,676
Reportable Segments [Member] \| Personal Insurance [Member]
Segment reporting information
Total assets	21,092	22,787
Other assets [Member]
Segment reporting information
Total assets	$ 1,183	$ 1,161

Amount of asset recognized for present right to economic benefit.

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+ Details

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details