Segment Information (Details) - Amortization and Depreciation - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Segment reporting information
Amortization and depreciation	$ 193	$ 188
Reportable Segments [Member]
Segment reporting information
Amortization and depreciation	191	186
Reportable Segments [Member] \| Business Insurance [Member]
Segment reporting information
Amortization and depreciation	114	113
Reportable Segments [Member] \| Bond & Specialty Insurance [Member]
Segment reporting information
Amortization and depreciation	27	23
Reportable Segments [Member] \| Personal Insurance [Member]
Segment reporting information
Amortization and depreciation	$ 50	$ 50

- 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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