Segment Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Segment Reporting Information
Earned premiums	$ 1,773	$ 1,593	$ 3,463	$ 3,137
Fee revenues	3	4	7	7
Other revenues	3	3	5	5
Investment income, net of expenses	195	175	380	349
Investment gains and losses, net	(1,154)	520	(1,820)	1,024
Total revenues	820	2,295	2,035	4,522
Income before Income Taxes	(1,041)	872	(1,401)	1,640
Identifiable Assets	29,192		29,192		$ 31,387
Consolidated Property And Casualty Insurance
Segment Reporting Information
Earned premiums	1,697	1,514	3,315	2,989
Identifiable Assets	4,945		4,945		4,421
Life Insurance Segment
Segment Reporting Information
Identifiable Assets	1,486		1,486		1,590
Investment Segment
Segment Reporting Information
Identifiable Assets	21,590		21,590		24,481
Corporate and Other
Segment Reporting Information
Identifiable Assets	1,171		1,171		$ 895
Operating Segments | Commercial Insurance
Segment Reporting Information
Earned premiums	994	911	1,956	1,797
Fee revenues	1	1	2	2
Total revenues	995	912	1,958	1,799
Income Before Income Taxes	(62)	145	14	275
Operating Segments | Commercial Insurance | Commercial Casualty Line
Segment Reporting Information
Earned premiums	350	312	686	615
Operating Segments | Commercial Insurance | Commercial Property Line
Segment Reporting Information
Earned premiums	280	259	554	512
Operating Segments | Commercial Insurance | Commercial Auto Line
Segment Reporting Information
Earned premiums	210	198	415	391
Operating Segments | Commercial Insurance | Workers' Compensation Line
Segment Reporting Information
Earned premiums	68	68	136	135
Operating Segments | Commercial Insurance | Other Commercial Lines
Segment Reporting Information
Earned premiums	86	74	165	144
Operating Segments | Personal Insurance
Segment Reporting Information
Earned premiums	413	382	815	758
Fee revenues	1	1	2	2
Total revenues	414	383	817	760
Income Before Income Taxes	(49)	29	16	26
Operating Segments | Personal Insurance | Personal Auto
Segment Reporting Information
Earned premiums	155	152	307	305
Operating Segments | Personal Insurance | Home Owner Line
Segment Reporting Information
Earned premiums	202	178	397	352
Operating Segments | Personal Insurance | Other Personal Lines
Segment Reporting Information
Earned premiums	56	52	111	101
Operating Segments | Excess and Surplus Lines Insurance
Segment Reporting Information
Earned premiums	124	95	236	184
Fee revenues	0	1	1	1
Total revenues	124	96	237	185
Income Before Income Taxes	19	10	35	18
Operating Segments | Life Insurance Segment
Segment Reporting Information
Earned premiums	76	79	148	148
Fee revenues	1	1	2	2
Total revenues	77	80	150	150
Income Before Income Taxes	13	(2)	11	(4)
Operating Segments | Investment Segment
Segment Reporting Information
Investment income, net of expenses	195	175	380	349
Investment gains and losses, net	(1,154)	520	(1,820)	1,024
Total revenues	(959)	695	(1,440)	1,373
Income Before Income Taxes	(987)	668	(1,495)	1,320
Corporate, Non-Segment
Segment Reporting Information
Total revenues	169	129	313	255
Corporate, Non-Segment | Reinsurance assumed and other non segment
Segment Reporting Information
Earned premiums	166	126	308	250
Corporate, Non-Segment | Corporate and Other
Segment Reporting Information
Other revenues	3	3	5	5
Income Before Income Taxes	$ 25	$ 22	$ 18	$ 5