Segment Information (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) industry segment	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Segment Reporting Information
Earned premiums									$ 5,604	$ 5,170	$ 4,954
Fee revenues									15	15	16
Other Income									9	5	5
Total revenues	$ 2,152	$ 1,700	$ 1,913	$ 2,159	$ 710	$ 1,915	$ 1,558	$ 1,224	7,924	5,407	5,732
Net Investment Income									646	619	609
Investment gains and losses, net									1,650	(402)	148
Income before income taxes	781	$ 294	$ 530	$ 867	(581)	$ 618	$ 264	$ (50)	2,472	251	730
Identifiable assets	25,408				21,935				$ 25,408	21,935
Number of Industries Operated In | industry									2
Number of Insurance Segments | segment									4
Life Insurance Segment
Segment Reporting Information
Earned premiums									$ 270	250	232
Identifiable assets	1,516				1,424				1,516	1,424
Investments Segment
Segment Reporting Information
Identifiable assets	19,583				16,741				19,583	16,741
Consolidated Property and Casualty Insurance Entity
Segment Reporting Information
Identifiable assets	3,437				3,285				3,437	3,285
Corporate and Other [Member]
Segment Reporting Information
Identifiable assets	$ 872				$ 485				872	485
Operating Segments | Commercial Insurance
Segment Reporting Information
Earned premiums									3,319	3,218	3,165
Fee revenues									5	5	5
Total revenues									3,324	3,223	3,170
Income before income taxes									241	151	119
Operating Segments | Commercial Insurance | Commercial Casualty Line
Segment Reporting Information
Earned premiums									1,102	1,075	1,072
Operating Segments | Commercial Insurance | Commercial Property Line
Segment Reporting Information
Earned premiums									958	920	903
Operating Segments | Commercial Insurance | Commercial Auto Line
Segment Reporting Information
Earned premiums									707	664	634
Operating Segments | Commercial Insurance | Workers' Compensation Line
Segment Reporting Information
Earned premiums									300	324	335
Operating Segments | Commercial Insurance | Other Commercial Lines
Segment Reporting Information
Earned premiums									252	235	221
Operating Segments | Personal Insurance
Segment Reporting Information
Earned premiums									1,404	1,336	1,241
Fee revenues									4	5	5
Total revenues									1,408	1,341	1,246
Income before income taxes									8	(20)	(32)
Operating Segments | Personal Insurance | Personal Auto
Segment Reporting Information
Earned premiums									621	614	582
Operating Segments | Personal Insurance | Home Owner Line
Segment Reporting Information
Earned premiums									607	563	518
Operating Segments | Personal Insurance | Other Personal Lines
Segment Reporting Information
Earned premiums									176	159	141
Operating Segments | Excess and Surplus Lines Insurance
Segment Reporting Information
Earned premiums									278	234	209
Fee revenues									2	1	1
Total revenues									280	235	210
Income before income taxes									53	63	61
Operating Segments | Life Insurance Segment
Segment Reporting Information
Earned premiums									270	250	232
Fee revenues									4	4	5
Total revenues									274	254	237
Income before income taxes									1	8	(1)
Operating Segments | Investments Segment
Segment Reporting Information
Total revenues									2,296	217	757
Net Investment Income									646	619	609
Investment gains and losses, net									1,650	(402)	148
Income before income taxes									2,197	121	664
Corporate, Non-Segment [Member]
Segment Reporting Information
Total revenues									342	137	112
Corporate, Non-Segment [Member] | Reinsurance assumed and other non segment
Segment Reporting Information
Earned premiums									333	132	107
Corporate, Non-Segment [Member] | Corporate and Other [Member]
Segment Reporting Information
Other Income									9	5	5
Income before income taxes									$ (28)	$ (72)	$ (81)