Segments of Operations - Earnings before income taxes by segment and sub-segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Earnings before realized gains (losses) and income taxes	$ 1,124	$ 1,113	$ 1,239
Realized gains (losses) on securities	0	(36)	(116)
Realized loss on subsidiary	0	(4)	0
Earnings before income taxes	1,124	1,073	1,123
Property and casualty insurance | Operating segments
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	620	631	776
Investment and other income, net	708	673	643
Earnings before realized gains (losses) and income taxes	1,328	1,304	1,419
Other | Operating segments
Segment Reporting Information [Line Items]
Earnings before realized gains (losses) and income taxes	(204)	(191)	(180)
Property and transportation | Property and casualty insurance | Operating segments
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	211	184	208
Specialty casualty | Property and casualty insurance | Operating segments
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	340	375	500
Specialty financial | Property and casualty insurance | Operating segments
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	134	110	114
Other specialty | Property and casualty insurance | Operating segments
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	(59)	(36)	(42)
Other lines | Property and casualty insurance | Operating segments
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	$ (6)	$ (2)	$ (4)