Segment Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Segment Reporting Information
Earned premiums	$ 1,690	$ 1,544
Fee revenues	4	3
Other revenues	2	2
Investment income, net of expenses	185	174
Investment gains and losses, net	(666)	504
Total revenues	1,215	2,227
Income before Income Taxes	(360)	768
Identifiable Assets	30,250		$ 31,387
Consolidated Property And Casualty Insurance
Segment Reporting Information
Earned premiums	1,618	1,475
Identifiable Assets	4,607		4,421
Life Insurance Segment
Segment Reporting Information
Identifiable Assets	1,577		1,590
Investment Segment
Segment Reporting Information
Identifiable Assets	23,201		24,481
Corporate and Other
Segment Reporting Information
Identifiable Assets	865		$ 895
Operating Segments | Commercial Insurance
Segment Reporting Information
Earned premiums	962	886
Fee revenues	1	1
Total revenues	963	887
Income Before Income Taxes	76	130
Operating Segments | Commercial Insurance | Commercial Casualty Line
Segment Reporting Information
Earned premiums	336	303
Operating Segments | Commercial Insurance | Commercial Property Line
Segment Reporting Information
Earned premiums	274	253
Operating Segments | Commercial Insurance | Commercial Auto Line
Segment Reporting Information
Earned premiums	205	193
Operating Segments | Commercial Insurance | Workers' Compensation Line
Segment Reporting Information
Earned premiums	67	67
Operating Segments | Commercial Insurance | Other Commercial Lines
Segment Reporting Information
Earned premiums	80	70
Operating Segments | Personal Insurance
Segment Reporting Information
Earned premiums	402	376
Fee revenues	1	1
Total revenues	403	377
Income Before Income Taxes	65	(3)
Operating Segments | Personal Insurance | Personal Auto
Segment Reporting Information
Earned premiums	152	152
Operating Segments | Personal Insurance | Home Owner Line
Segment Reporting Information
Earned premiums	195	174
Operating Segments | Personal Insurance | Other Personal Lines
Segment Reporting Information
Earned premiums	55	50
Operating Segments | Excess and Surplus Lines Insurance
Segment Reporting Information
Earned premiums	112	89
Fee revenues	1	0
Total revenues	113	89
Income Before Income Taxes	16	8
Operating Segments | Life Insurance Segment
Segment Reporting Information
Earned premiums	72	69
Fee revenues	1	1
Total revenues	73	70
Income Before Income Taxes	(2)	(2)
Operating Segments | Investment Segment
Segment Reporting Information
Investment income, net of expenses	185	174
Investment gains and losses, net	(666)	504
Total revenues	(481)	678
Income Before Income Taxes	(508)	652
Corporate, Non-Segment
Segment Reporting Information
Total revenues	144	126
Corporate, Non-Segment | Reinsurance assumed and other non segment
Segment Reporting Information
Earned premiums	142	124
Corporate, Non-Segment | Corporate and Other
Segment Reporting Information
Other revenues	2	2
Income Before Income Taxes	$ (7)	$ (17)