Segment Information (Details) - Amortization and Depreciation - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Segment reporting information
Amortization and depreciation			$ 518	$ 552
Reportable Segments [Member]
Segment reporting information
Amortization and depreciation	$ 164	$ 173	513	547
Reportable Segments [Member] \| Business Insurance [Member]
Segment reporting information
Amortization and depreciation	99	102	312	330
Reportable Segments [Member] \| Bond & Specialty Insurance [Member]
Segment reporting information
Amortization and depreciation	21	21	62	66
Reportable Segments [Member] \| Personal Insurance [Member]
Segment reporting information
Amortization and depreciation	$ 44	$ 50	$ 139	$ 151

- Definition

The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

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