Segment Information (Details) - Assets by Segment - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Assets by segment
Total assets	$ 143,678	$ 133,189
Reportable Segments [Member]
Assets by segment
Total assets	142,602	132,077
Reportable Segments [Member] \| Business Insurance [Member]
Assets by segment
Total assets	106,018	98,311
Reportable Segments [Member] \| Bond & Specialty Insurance [Member]
Assets by segment
Total assets	13,767	12,628
Reportable Segments [Member] \| Personal Insurance [Member]
Assets by segment
Total assets	22,817	21,138
Other assets [Member]
Assets by segment
Total assets	$ 1,076	$ 1,112

Amount of asset recognized for present right to economic benefit.

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+ Details