Segments of Operations - Revenues by segment and sub-segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Net earned premiums	$ 6,085	$ 5,404	$ 5,099
Net investment income	717	730	461
Other income	117	113	80
Revenues before realized gains (losses)	7,156	6,438	5,821
Realized gains (losses) on securities	(116)	110	(75)
Realized gains on subsidiaries	0	4	23
Total revenues	7,040	6,552	5,769
Property and casualty insurance
Segment Reporting Information [Line Items]
Net earned premiums	6,085	5,404	5,099
Net investment income	683	663	399
Other income	12	27	8
Revenues before realized gains (losses)	6,780	6,094	5,506
Other
Segment Reporting Information [Line Items]
Revenues before realized gains (losses)	376	293	266
Other | Real estate-related investments | Continuing operations
Segment Reporting Information [Line Items]
Net investment income	0	51	49
Property and transportation | Property and casualty insurance
Segment Reporting Information [Line Items]
Net earned premiums	2,487	2,144	1,871
Specialty casualty | Property and casualty insurance
Segment Reporting Information [Line Items]
Net earned premiums	2,659	2,408	2,235
Specialty financial | Property and casualty insurance
Segment Reporting Information [Line Items]
Net earned premiums	698	642	613
Other specialty | Property and casualty insurance
Segment Reporting Information [Line Items]
Net earned premiums	241	210	180
Other lines | Property and casualty insurance
Segment Reporting Information [Line Items]
Net earned premiums	$ 0	$ 0	$ 200