Segment Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Segment Reporting Information
Assets	$ 23,367		$ 25,408
Earned premiums	1,456	$ 1,333
Fee revenues	3	4
Other revenues	2	2
Investment income, net of expenses	165	157
Investment gains and losses, net	(1,725)	663
Total revenues	(99)	2,159
Income Before Income Taxes	(1,576)	867
Consolidated Property and Casualty Insurance Entity
Segment Reporting Information
Assets	3,444		3,437
Life Insurance Segment
Segment Reporting Information
Assets	1,517		1,516
Investments Segment
Segment Reporting Information
Assets	17,699		19,583
Corporate, Non-Segment
Segment Reporting Information
Assets	707		$ 872
Other revenues	2	2
Total revenues	91	52
Income Before Income Taxes	(2)	(11)
Corporate, Non-Segment | Reinsurance assumed and other non segment
Segment Reporting Information
Earned premiums	89	50
Operating Segments | Commercial Lines
Segment Reporting Information
Earned premiums	863	810
Fee revenues	1	1
Total revenues	864	811
Income Before Income Taxes	(20)	76
Operating Segments | Personal Lines
Segment Reporting Information
Earned premiums	359	344
Fee revenues	1	1
Total revenues	360	345
Income Before Income Taxes	21	(4)
Operating Segments | Excess and Surplus Lines Insurance
Segment Reporting Information
Earned premiums	78	63
Fee revenues	1	1
Total revenues	79	64
Income Before Income Taxes	9	11
Operating Segments | Life Insurance Segment
Segment Reporting Information
Earned premiums	67	66
Fee revenues	0	1
Total revenues	67	67
Income Before Income Taxes	2	(1)
Operating Segments | Investments Segment
Segment Reporting Information
Investment income, net of expenses	165	157
Investment gains and losses, net	(1,725)	663
Total revenues	(1,560)	820
Income Before Income Taxes	(1,586)	796
Commercial Casualty | Operating Segments | Commercial Lines
Segment Reporting Information
Earned premiums	289	268
Commercial Property | Operating Segments | Commercial Lines
Segment Reporting Information
Earned premiums	249	234
Commercial Auto | Operating Segments | Commercial Lines
Segment Reporting Information
Earned premiums	185	170
Workers' Compensation | Operating Segments | Commercial Lines
Segment Reporting Information
Earned premiums	75	77
Other Commercial Lines | Operating Segments | Commercial Lines
Segment Reporting Information
Earned premiums	65	61
Personal Auto | Operating Segments | Personal Lines
Segment Reporting Information
Earned premiums	154	155
Home Owner Segment | Operating Segments | Personal Lines
Segment Reporting Information
Earned premiums	159	147
Other Personal Lines | Operating Segments | Personal Lines
Segment Reporting Information
Earned premiums	$ 46	$ 42