Segments of Operations - Revenues by segment and sub-segment (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Segment Reporting Information [Line Items]
Total premiums earned	$ 1,393	$ 1,250	$ 2,695	$ 2,423
Net investment income	168	164	398	352
Other income	32	20	62	43
Revenues before realized gains (losses)	1,632	1,484	3,235	2,916
Realized gains (losses) on securities	(93)	43	(108)	120
Total revenues	1,539	1,531	3,127	3,040
Property and Casualty Insurance
Segment Reporting Information [Line Items]
Total premiums earned	1,393	1,250	2,695	2,423
Net investment income	156	143	379	302
Other income	6	1	10	5
Revenues before realized gains (losses)	1,555	1,394	3,084	2,730
Other
Segment Reporting Information [Line Items]
Revenues before realized gains (losses)	77	68	151	135
Other | Real estate-related entities | Continuing operations
Segment Reporting Information [Line Items]
Net investment income	0	22	0	51
Property and transportation | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Total premiums earned	505	453	948	847
Specialty casualty | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Total premiums earned	657	588	1,296	1,159
Specialty financial | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Total premiums earned	171	157	334	314
Other specialty | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Total premiums earned	$ 60	$ 52	$ 117	$ 103