Segments of Operations - Revenues by segment and sub-segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Net earned premiums	$ 5,404	$ 5,099	$ 5,185
Net investment income	730	461	532
Other income	113	80	86
Revenues before realized gains (losses)	6,438	5,821	6,058
Realized gains (losses) on securities	110	(75)	155
Realized gains on subsidiaries	4	23	0
Total revenues	6,552	5,769	6,213
Real estate-related investments | Continuing operations
Segment Reporting Information [Line Items]
Net investment income	51	49	37
Property and casualty insurance
Segment Reporting Information [Line Items]
Net earned premiums	5,404	5,099	5,185
Net investment income	663	399	472
Other income	27	8	11
Revenues before realized gains (losses)	6,094	5,506	5,668
Other
Segment Reporting Information [Line Items]
Revenues before realized gains (losses)	293	266	353
Other | Real estate-related investments | Continuing operations
Segment Reporting Information [Line Items]
Net investment income	51	49	37
Property and transportation | Property and casualty insurance
Segment Reporting Information [Line Items]
Net earned premiums	2,144	1,871	1,828
Specialty casualty | Property and casualty insurance
Segment Reporting Information [Line Items]
Net earned premiums	2,408	2,235	2,597
Specialty financial | Property and casualty insurance
Segment Reporting Information [Line Items]
Net earned premiums	642	613	610
Other specialty | Property and casualty insurance
Segment Reporting Information [Line Items]
Net earned premiums	210	180	150
Other lines | Property and casualty insurance
Segment Reporting Information [Line Items]
Net earned premiums	$ 0	$ 200	$ 0