Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Segment Reporting Information
Earned premiums	$ 1,943	$ 1,773	$ 3,861	$ 3,466
Fee revenues	6	3	10	7
Investment income, net of expenses	220	195	430	380
Investment gains and losses, net	434	(1,154)	540	(1,820)
Other revenues	2	3	5	5
Total revenues	2,605	820	4,846	2,038
Income before Income Taxes	666	(1,053)	934	(1,404)
Assets	31,352		31,352		$ 29,732
Consolidated Property And Casualty Insurance
Segment Reporting Information
Earned premiums	1,863	1,697	3,704	3,315
Assets	5,354		5,354		5,178
Life Insurance Segment
Segment Reporting Information
Assets	1,542		1,542		1,518
Investment Segment
Segment Reporting Information
Assets	23,535		23,535		22,133
Corporate and Other
Segment Reporting Information
Assets	921		921		$ 903
Operating Segments | Commercial Insurance
Segment Reporting Information
Earned premiums	1,066	994	2,122	1,956
Fee revenues	1	1	2	2
Total revenues	1,067	995	2,124	1,958
Income Before Income Taxes	33	(62)	31	14
Operating Segments | Commercial Insurance | Commercial Casualty Line
Segment Reporting Information
Earned premiums	373	350	750	686
Operating Segments | Commercial Insurance | Commercial Property Line
Segment Reporting Information
Earned premiums	312	280	611	554
Operating Segments | Commercial Insurance | Commercial Auto Line
Segment Reporting Information
Earned premiums	214	210	428	415
Operating Segments | Commercial Insurance | Workers' Compensation Line
Segment Reporting Information
Earned premiums	72	68	146	136
Operating Segments | Commercial Insurance | Other Commercial Lines
Segment Reporting Information
Earned premiums	95	86	187	165
Operating Segments | Personal Insurance
Segment Reporting Information
Earned premiums	493	413	957	815
Fee revenues	1	1	2	2
Total revenues	494	414	959	817
Income Before Income Taxes	(36)	(49)	(93)	16
Operating Segments | Personal Insurance | Personal Auto
Segment Reporting Information
Earned premiums	173	155	339	307
Operating Segments | Personal Insurance | Home Owner Line
Segment Reporting Information
Earned premiums	251	202	484	397
Operating Segments | Personal Insurance | Other Personal Lines
Segment Reporting Information
Earned premiums	69	56	134	111
Operating Segments | Excess and Surplus Lines Insurance
Segment Reporting Information
Earned premiums	132	124	259	236
Fee revenues	1	0	1	1
Total revenues	133	124	260	237
Income Before Income Taxes	11	19	24	35
Operating Segments | Life Insurance Segment
Segment Reporting Information
Earned premiums	80	76	157	151
Fee revenues	3	1	5	2
Total revenues	83	77	162	153
Income Before Income Taxes	13	1	21	8
Operating Segments | Investment Segment
Segment Reporting Information
Investment income, net of expenses	220	195	430	380
Investment gains and losses, net	434	(1,154)	540	(1,820)
Total revenues	654	(959)	970	(1,440)
Income Before Income Taxes	624	(987)	910	(1,495)
Corporate, Non-Segment
Segment Reporting Information
Total revenues	174	169	371	313
Corporate, Non-Segment | Reinsurance assumed and other non segment
Segment Reporting Information
Earned premiums	172	166	366	308
Corporate, Non-Segment | Corporate and Other
Segment Reporting Information
Other revenues	2	3	5	5
Income Before Income Taxes	$ 21	$ 25	$ 41	$ 18