Segments of Operations - Revenues by segment and sub-segment (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Segment Reporting Information [Line Items]
Total premiums earned	$ 1,302	$ 1,173
Net investment income	230	188
Other income	30	23
Revenues before realized gains (losses)	1,603	1,432
Realized gains (losses) on securities	(15)	77
Total revenues	1,588	1,509
Property and Casualty Insurance
Segment Reporting Information [Line Items]
Total premiums earned	1,302	1,173
Net investment income	223	159
Other income	4	4
Revenues before realized gains (losses)	1,529	1,336
Other
Segment Reporting Information [Line Items]
Revenues before realized gains (losses)	74	67
Other | Real estate-related entities | Continuing operations
Segment Reporting Information [Line Items]
Net investment income	0	29
Property and transportation | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Total premiums earned	443	394
Specialty casualty | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Total premiums earned	639	571
Specialty financial | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Total premiums earned	163	157
Other specialty | Property and Casualty Insurance
Segment Reporting Information [Line Items]
Total premiums earned	$ 57	$ 51