Segments of Operations - Earnings before income taxes by segment and sub-segment (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Segment Reporting Information [Line Items]
Earnings before realized gains and income taxes	$ 194	$ 290
Realized gains on securities	3	14
Earnings before income taxes	197	304
Operating segments | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	94	153
Investment and other income, net	152	187
Earnings before realized gains and income taxes	246	340
Operating segments | Property and Casualty Insurance | Property and transportation
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	37	60
Operating segments | Property and Casualty Insurance | Specialty casualty
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	20	61
Operating segments | Property and Casualty Insurance | Specialty financial
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	37	33
Operating segments | Property and Casualty Insurance | Other lines
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	0	(1)
Operating segments | Other
Segment Reporting Information [Line Items]
Earnings before realized gains and income taxes	$ (52)	$ (50)