Segment Information - Revenues (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Segment Reporting Information [Line Items]
Earned premiums and fee income	$ 5,779	$ 5,382
Net investment income	593	515
Net realized gains (losses)	28	(7)
Other revenues	19	20
Total revenues	6,419	5,910
Corporate
Segment Reporting Information [Line Items]
Earned premiums and fee income	10	9
Commercial Lines | Operating Segments [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income	3,059	2,776
Commercial Lines | Operating Segments [Member] | Workers’ compensation
Segment Reporting Information [Line Items]
Earned premiums and fee income	917	898
Commercial Lines | Operating Segments [Member] | Liability
Segment Reporting Information [Line Items]
Earned premiums and fee income	526	486
Commercial Lines | Operating Segments [Member] | Marine
Segment Reporting Information [Line Items]
Earned premiums and fee income	67	59
Commercial Lines | Operating Segments [Member] | Package business
Segment Reporting Information [Line Items]
Earned premiums and fee income	549	484
Commercial Lines | Operating Segments [Member] | Property
Segment Reporting Information [Line Items]
Earned premiums and fee income	290	228
Commercial Lines | Operating Segments [Member] | Professional liability
Segment Reporting Information [Line Items]
Earned premiums and fee income	203	188
Commercial Lines | Operating Segments [Member] | Bond
Segment Reporting Information [Line Items]
Earned premiums and fee income	78	77
Commercial Lines | Operating Segments [Member] | Assumed reinsurance
Segment Reporting Information [Line Items]
Earned premiums and fee income	181	138
Commercial Lines | Operating Segments [Member] | Automobile
Segment Reporting Information [Line Items]
Earned premiums and fee income	248	218
Personal Lines | AARP Members [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income	758	689
Personal Lines | Operating Segments [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income	821	747
Personal Lines | Operating Segments [Member] | Property
Segment Reporting Information [Line Items]
Earned premiums and fee income	249	232
Personal Lines | Operating Segments [Member] | Automobile
Segment Reporting Information [Line Items]
Earned premiums and fee income	572	515
Group Benefits | Operating Segments [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income	1,639	1,609
Group Benefits | Operating Segments [Member] | Group disability
Segment Reporting Information [Line Items]
Earned premiums and fee income	890	866
Group Benefits | Operating Segments [Member] | Group life
Segment Reporting Information [Line Items]
Earned premiums and fee income	645	643
Group Benefits | Operating Segments [Member] | Other
Segment Reporting Information [Line Items]
Earned premiums and fee income	104	100
Hartford Funds | Operating Segments [Member]
Segment Reporting Information [Line Items]
Earned premiums and fee income	250	241
Hartford Funds | Operating Segments [Member] | Mutual fund and ETF
Segment Reporting Information [Line Items]
Earned premiums and fee income	231	223
Hartford Funds | Operating Segments [Member] | Third-party life and annuity separate accounts
Segment Reporting Information [Line Items]
Earned premiums and fee income	$ 19	$ 18