Segment Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($) industry segment	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Segment Reporting Information
Earned premiums	$ 7,219	$ 6,482	$ 5,980
Fee revenues	14	15	11
Other	10	10	10
Investment income, net of expenses	781	714	670
Total revenues	6,557	9,630	7,536
Total income before income taxes	(693)	3,670	1,499
Total assets	$ 29,736	31,387
Number of Industries Operated In | industry	2
Number of Insurance Segments | segment	4
Consolidated Property And Casualty Insurance Entity
Segment Reporting Information
Total assets	$ 5,178	4,421
Life Insurance Segment
Segment Reporting Information
Earned premiums	295	298	289
Total assets	1,522	1,590
Investments Segment
Segment Reporting Information
Total assets	22,133	24,481
Corporate and Other
Segment Reporting Information
Total assets	903	895
Operating Segments | Commercial Insurance
Segment Reporting Information
Earned premiums	4,024	3,674	3,476
Fee revenues	4	4	3
Total revenues	4,028	3,678	3,479
Income (loss) before income taxes	38	598	64
Operating Segments | Commercial Insurance | Commercial Casualty Line
Segment Reporting Information
Earned premiums	1,416	1,270	1,165
Operating Segments | Commercial Insurance | Commercial Property Segment [Member]
Segment Reporting Information
Earned premiums	1,136	1,043	1,010
Operating Segments | Commercial Insurance | Commercial Auto Line
Segment Reporting Information
Earned premiums	842	794	755
Operating Segments | Commercial Insurance | Workers' Compensation Line
Segment Reporting Information
Earned premiums	284	268	271
Operating Segments | Commercial Insurance | Other Commercial Lines
Segment Reporting Information
Earned premiums	346	299	275
Operating Segments | Personal Insurance
Segment Reporting Information
Earned premiums	1,689	1,542	1,463
Fee revenues	4	4	4
Total revenues	1,693	1,546	1,467
Income (loss) before income taxes	18	97	47
Operating Segments | Personal Insurance | Personal Auto
Segment Reporting Information
Earned premiums	626	609	615
Operating Segments | Personal Insurance | Home Owner Line
Segment Reporting Information
Earned premiums	829	726	658
Operating Segments | Personal Insurance | Other Personal Lines
Segment Reporting Information
Earned premiums	234	207	190
Operating Segments | Excess and Surplus Lines Insurance
Segment Reporting Information
Earned premiums	485	398	325
Fee revenues	2	2	2
Total revenues	487	400	327
Income (loss) before income taxes	48	44	34
Operating Segments | Life Insurance Segment
Segment Reporting Information
Earned premiums	295	298	289
Fee revenues	4	5	2
Total revenues	299	303	291
Income (loss) before income taxes	28	(16)	11
Operating Segments | Investments Segment
Segment Reporting Information
Investment income, net of expenses	781	714	670
Investment gains and losses, net	(1,467)	2,409	865
Total revenues	(686)	3,123	1,535
Income (loss) before income taxes	(795)	3,018	1,433
Corporate, Non-Segment
Segment Reporting Information
Total revenues	736	580	437
Corporate, Non-Segment | Reinsurance assumed and other non segment
Segment Reporting Information
Earned premiums	726	570	427
Corporate, Non-Segment | Corporate and Other
Segment Reporting Information
Other	10	10	10
Income (loss) before income taxes	$ (30)	$ (71)	$ (90)