Segment Reporting (Details) - Amortization and Depreciation - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Segment reporting information
Amortization and depreciation			$ 352	$ 378
Reportable Segments [Member]
Segment reporting information
Amortization and depreciation	$ 163	$ 180	349	374
Reportable Segments [Member] \| Business Insurance [Member]
Segment reporting information
Amortization and depreciation	100	111	213	228
Reportable Segments [Member] \| Bond & Specialty Insurance [Member]
Segment reporting information
Amortization and depreciation	18	21	41	45
Reportable Segments [Member] \| Personal Insurance [Member]
Segment reporting information
Amortization and depreciation	$ 45	$ 48	$ 95	$ 101

- 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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