Segment Information - Revenues (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Segment Reporting Information [Line Items]
Earned premiums and fee income	$ 5,917	$ 5,548	$ 11,696	$ 10,930
Net investment income	602	540	1,195	1,055
Net realized losses	(59)	(64)	(31)	(71)
Other revenues	26	25	45	45
Total revenues	6,486	6,049	12,905	11,959
Corporate
Segment Reporting Information [Line Items]
Earned premiums and fee income	10	11	20	20
Commercial Lines \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income	3,132	2,896	6,191	5,672
Commercial Lines \| Operating Segments [Member] \| Workers’ compensation
Segment Reporting Information [Line Items]
Earned premiums and fee income	926	924	1,843	1,822
Commercial Lines \| Operating Segments [Member] \| Liability
Segment Reporting Information [Line Items]
Earned premiums and fee income	540	502	1,066	988
Commercial Lines \| Operating Segments [Member] \| Marine
Segment Reporting Information [Line Items]
Earned premiums and fee income	67	66	134	125
Commercial Lines \| Operating Segments [Member] \| Package business
Segment Reporting Information [Line Items]
Earned premiums and fee income	572	514	1,121	998
Commercial Lines \| Operating Segments [Member] \| Property
Segment Reporting Information [Line Items]
Earned premiums and fee income	306	244	596	472
Commercial Lines \| Operating Segments [Member] \| Professional liability
Segment Reporting Information [Line Items]
Earned premiums and fee income	200	196	403	384
Commercial Lines \| Operating Segments [Member] \| Bond
Segment Reporting Information [Line Items]
Earned premiums and fee income	80	80	158	157
Commercial Lines \| Operating Segments [Member] \| Assumed reinsurance
Segment Reporting Information [Line Items]
Earned premiums and fee income	180	143	361	281
Commercial Lines \| Operating Segments [Member] \| Automobile
Segment Reporting Information [Line Items]
Earned premiums and fee income	261	227	509	445
Personal Lines \| AARP Members [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income	788	710	1,550	1,400
Personal Lines \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income	857	767	1,678	1,514
Personal Lines \| Operating Segments [Member] \| Property
Segment Reporting Information [Line Items]
Earned premiums and fee income	259	239	508	471
Personal Lines \| Operating Segments [Member] \| Automobile
Segment Reporting Information [Line Items]
Earned premiums and fee income	598	528	1,170	1,043
Group Benefits \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income	1,665	1,630	3,304	3,239
Group Benefits \| Operating Segments [Member] \| Group disability
Segment Reporting Information [Line Items]
Earned premiums and fee income	895	878	1,785	1,744
Group Benefits \| Operating Segments [Member] \| Group life
Segment Reporting Information [Line Items]
Earned premiums and fee income	663	650	1,308	1,293
Group Benefits \| Operating Segments [Member] \| Other
Segment Reporting Information [Line Items]
Earned premiums and fee income	107	102	211	202
Hartford Funds \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income	253	244	503	485
Hartford Funds \| Operating Segments [Member] \| Mutual fund and ETF
Segment Reporting Information [Line Items]
Earned premiums and fee income	235	226	466	449
Hartford Funds \| Operating Segments [Member] \| Third-party life and annuity separate accounts
Segment Reporting Information [Line Items]
Earned premiums and fee income	$ 18	$ 18	$ 37	$ 36