Segment Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) segment industry	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Segment Reporting Information
Earned premiums	$ 6,482	$ 5,980	$ 5,604
Fee revenues	15	11	15
Other Income	10	10	9
Total revenues	9,630	7,536	7,924
Net Investment Income	714	670	646
Investment gains and losses, net	2,409	865	1,650
Total income before income taxes	3,670	1,499	2,472
Identifiable assets	$ 31,387	27,542
Number of Industries Operated In | industry	2
Number of Insurance Segments | segment	4
Consolidated Property And Casualty Insurance Entity
Segment Reporting Information
Identifiable assets	$ 4,421	3,838
Life Insurance Segment
Segment Reporting Information
Earned premiums	298	289	270
Identifiable assets	1,590	1,661
Investments Segment
Segment Reporting Information
Identifiable assets	24,481	21,332
Corporate and Other [Member]
Segment Reporting Information
Identifiable assets	895	711
Operating Segments | Commercial Insurance
Segment Reporting Information
Earned premiums	3,674	3,476	3,319
Fee revenues	4	3	5
Total revenues	3,678	3,479	3,324
Income (loss) before income taxes	598	64	241
Operating Segments | Commercial Insurance | Commercial Casualty Line
Segment Reporting Information
Earned premiums	1,270	1,165	1,102
Operating Segments | Commercial Insurance | Commercial Property Line
Segment Reporting Information
Earned premiums	1,043	1,010	958
Operating Segments | Commercial Insurance | Commercial Auto Line
Segment Reporting Information
Earned premiums	794	755	707
Operating Segments | Commercial Insurance | Workers' Compensation Line
Segment Reporting Information
Earned premiums	268	271	300
Operating Segments | Commercial Insurance | Other Commercial Lines
Segment Reporting Information
Earned premiums	299	275	252
Operating Segments | Personal Insurance
Segment Reporting Information
Earned premiums	1,542	1,463	1,404
Fee revenues	4	4	4
Total revenues	1,546	1,467	1,408
Income (loss) before income taxes	97	47	8
Operating Segments | Personal Insurance | Personal Auto
Segment Reporting Information
Earned premiums	609	615	621
Operating Segments | Personal Insurance | Home Owner Line
Segment Reporting Information
Earned premiums	726	658	607
Operating Segments | Personal Insurance | Other Personal Lines
Segment Reporting Information
Earned premiums	207	190	176
Operating Segments | Excess and Surplus Lines Insurance
Segment Reporting Information
Earned premiums	398	325	278
Fee revenues	2	2	2
Total revenues	400	327	280
Income (loss) before income taxes	44	34	53
Operating Segments | Life Insurance Segment
Segment Reporting Information
Earned premiums	298	289	270
Fee revenues	5	2	4
Total revenues	303	291	274
Income (loss) before income taxes	(16)	11	1
Operating Segments | Investments Segment
Segment Reporting Information
Total revenues	3,123	1,535	2,296
Net Investment Income	714	670	646
Investment gains and losses, net	2,409	865	1,650
Income (loss) before income taxes	3,018	1,433	2,197
Corporate, Non-Segment
Segment Reporting Information
Total revenues	580	437	342
Corporate, Non-Segment | Reinsurance assumed and other non segment
Segment Reporting Information
Earned premiums	570	427	333
Corporate, Non-Segment | Corporate and Other [Member]
Segment Reporting Information
Other Income	10	10	9
Income (loss) before income taxes	$ (71)	$ (90)	$ (28)