Segment Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Segment Reporting Information
Earned premiums	$ 1,882	$ 1,669	$ 5,345	$ 4,806
Fee revenues	5	4	12	11
Other revenues	2	3	7	8
Investment income, net of expenses	193	179	573	528
Investment gains and losses, net	(674)	(70)	(2,494)	954
Total revenues	1,408	1,785	3,443	6,307
Income before Income Taxes	(579)	184	(1,980)	1,824
Identifiable Assets	28,199		28,199		$ 31,387
Consolidated Property And Casualty Insurance
Segment Reporting Information
Earned premiums	1,809	1,596	5,124	4,585
Identifiable Assets	5,072		5,072		4,421
Life Insurance Segment
Segment Reporting Information
Identifiable Assets	1,525		1,525		1,590
Investment Segment
Segment Reporting Information
Identifiable Assets	20,726		20,726		24,481
Corporate and Other
Segment Reporting Information
Identifiable Assets	876		876		$ 895
Operating Segments | Commercial Insurance
Segment Reporting Information
Earned premiums	1,028	930	2,984	2,727
Fee revenues	1	1	3	3
Total revenues	1,029	931	2,987	2,730
Income Before Income Taxes	11	182	25	457
Operating Segments | Commercial Insurance | Commercial Casualty Line
Segment Reporting Information
Earned premiums	360	323	1,046	938
Operating Segments | Commercial Insurance | Commercial Property Line
Segment Reporting Information
Earned premiums	292	264	846	776
Operating Segments | Commercial Insurance | Commercial Auto Line
Segment Reporting Information
Earned premiums	213	200	627	591
Operating Segments | Commercial Insurance | Workers' Compensation Line
Segment Reporting Information
Earned premiums	73	66	209	201
Operating Segments | Commercial Insurance | Other Commercial Lines
Segment Reporting Information
Earned premiums	90	77	256	221
Operating Segments | Personal Insurance
Segment Reporting Information
Earned premiums	431	388	1,246	1,146
Fee revenues	1	1	3	3
Total revenues	432	389	1,249	1,149
Income Before Income Taxes	(18)	(10)	(2)	16
Operating Segments | Personal Insurance | Personal Auto
Segment Reporting Information
Earned premiums	158	153	465	457
Operating Segments | Personal Insurance | Home Owner Line
Segment Reporting Information
Earned premiums	213	184	609	536
Operating Segments | Personal Insurance | Other Personal Lines
Segment Reporting Information
Earned premiums	60	51	172	153
Operating Segments | Excess and Surplus Lines Insurance
Segment Reporting Information
Earned premiums	125	105	361	289
Fee revenues	1	1	2	2
Total revenues	126	106	363	291
Income Before Income Taxes	9	7	44	25
Operating Segments | Life Insurance Segment
Segment Reporting Information
Earned premiums	73	73	221	221
Fee revenues	2	1	4	3
Total revenues	75	74	225	224
Income Before Income Taxes	11	(5)	22	(9)
Operating Segments | Investment Segment
Segment Reporting Information
Investment income, net of expenses	193	179	573	528
Investment gains and losses, net	(674)	(70)	(2,494)	954
Total revenues	(481)	109	(1,921)	1,482
Income Before Income Taxes	(508)	83	(2,003)	1,403
Corporate, Non-Segment
Segment Reporting Information
Total revenues	227	176	540	431
Corporate, Non-Segment | Reinsurance assumed and other non segment
Segment Reporting Information
Earned premiums	225	173	533	423
Corporate, Non-Segment | Corporate and Other
Segment Reporting Information
Other revenues	2	3	7	8
Income Before Income Taxes	$ (84)	$ (73)	$ (66)	$ (68)