Segment Information - Revenues (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Segment Reporting Information [Line Items]
Earned premiums and fee income	$ 6,081	$ 5,640	$ 17,777	$ 16,570
Net investment income	659	597	1,854	1,652
Net realized losses	(13)	(90)	(44)	(161)
Other revenues	24	21	69	66
Total revenues	6,751	6,168	19,656	18,127
Personal Lines \| AARP Members [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income	817	731	2,360	2,130
Operating Segments [Member] \| Commercial Lines
Segment Reporting Information [Line Items]
Earned premiums and fee income	3,260	2,962	9,451	8,634
Operating Segments [Member] \| Personal Lines
Segment Reporting Information [Line Items]
Earned premiums and fee income	893	791	2,571	2,305
Operating Segments [Member] \| Group Benefits
Segment Reporting Information [Line Items]
Earned premiums and fee income	1,655	1,629	4,959	4,868
Operating Segments [Member] \| Hartford Funds
Segment Reporting Information [Line Items]
Earned premiums and fee income	263	248	766	733
Operating Segments [Member] \| Hartford Funds \| Mutual fund and ETF
Segment Reporting Information [Line Items]
Earned premiums and fee income	244	229	710	678
Operating Segments [Member] \| Hartford Funds \| Third-party life and annuity separate accounts
Segment Reporting Information [Line Items]
Earned premiums and fee income	19	19	56	55
Operating Segments [Member] \| Workers’ compensation \| Commercial Lines
Segment Reporting Information [Line Items]
Earned premiums and fee income	933	919	2,776	2,741
Operating Segments [Member] \| Liability \| Commercial Lines
Segment Reporting Information [Line Items]
Earned premiums and fee income	575	522	1,641	1,510
Operating Segments [Member] \| Marine \| Commercial Lines
Segment Reporting Information [Line Items]
Earned premiums and fee income	71	67	205	192
Operating Segments [Member] \| Package business \| Commercial Lines
Segment Reporting Information [Line Items]
Earned premiums and fee income	593	534	1,714	1,532
Operating Segments [Member] \| Property \| Commercial Lines
Segment Reporting Information [Line Items]
Earned premiums and fee income	325	250	921	722
Operating Segments [Member] \| Property \| Personal Lines
Segment Reporting Information [Line Items]
Earned premiums and fee income	272	245	780	716
Operating Segments [Member] \| Professional liability \| Commercial Lines
Segment Reporting Information [Line Items]
Earned premiums and fee income	209	198	612	582
Operating Segments [Member] \| Bond \| Commercial Lines
Segment Reporting Information [Line Items]
Earned premiums and fee income	82	82	240	239
Operating Segments [Member] \| Assumed reinsurance \| Commercial Lines
Segment Reporting Information [Line Items]
Earned premiums and fee income	194	156	555	437
Operating Segments [Member] \| Automobile \| Commercial Lines
Segment Reporting Information [Line Items]
Earned premiums and fee income	278	234	787	679
Operating Segments [Member] \| Automobile \| Personal Lines
Segment Reporting Information [Line Items]
Earned premiums and fee income	621	546	1,791	1,589
Operating Segments [Member] \| Group disability \| Group Benefits
Segment Reporting Information [Line Items]
Earned premiums and fee income	889	884	2,674	2,628
Operating Segments [Member] \| Group life \| Group Benefits
Segment Reporting Information [Line Items]
Earned premiums and fee income	659	643	1,967	1,936
Operating Segments [Member] \| Other \| Group Benefits
Segment Reporting Information [Line Items]
Earned premiums and fee income	107	102	318	304
Corporate
Segment Reporting Information [Line Items]
Earned premiums and fee income	$ 10	$ 10	$ 30	$ 30